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01101001
2016-Jan-12, 04:47 AM
Discovery: Gravitational Wave Rumors Rumble Social Media (http://news.discovery.com/space/gravitational-wave-discovery-rumors-rumble-social-media-160111.htm)


In a tweet by Lawrence Krauss this morning, the well-known Arizona State University theoretical physicist and cosmologist wrote: “My earlier rumor about LIGO has been confirmed by independent sources. Stay tuned! Gravitational waves may have been discovered!! Exciting.”

These waves are a roller coaster ride.

antoniseb
2016-Jan-12, 12:45 PM
We should wait till there is a result before discussing it in detail. I would like for there to be a result, but I think it is likely it will be barely distinguishable from noise. The best thing about a result will be that it justifies using even more money to look with bigger/better tools.

John Mendenhall
2016-Jan-12, 07:06 PM
Hope so. But as Tony says, don't go off the deep end believing what we want to believe. First, peer review, second, reproduciable results. For right now, wait and see.

kevin1981
2016-Jan-13, 02:10 AM
Wasn't it only two or three years ago that people were getting exciting over neutrino's possibly travelling faster than light... Lets remember how that turned out !

Ken G
2016-Jan-13, 06:51 AM
Actually, I think this would be a lot different-- no one got that excited about the neutrinos that I know, we all pretty much expected the other shoe to drop. It was a very difficult measurement, and we had plenty of reason to doubt it was true. For gravitational waves, it's also a difficult measurement, but we have every reason to expect it is true-- due to binary pulsar data. No one was saying "if we don't detect superluminal neutrinos soon, we are badly mixed up about something"-- but that's just the situation with gravitational waves. We'd like to detect them, to show that physics works, but we'd also like to not detect them-- to show that there's more to know! So in a way, it's almost too much to hope that LIGO won't detect them.

John Mendenhall
2016-Jan-13, 08:44 AM
Hm, yes, good point, KenG.

01101001
2016-Feb-11, 02:59 AM
Rumor: 29 + 36 = 62 + 3

Science: ‘Woohoo!’ email stokes rumor that gravitational waves have been spotted (http://www.sciencemag.org/news/2016/02/woohoo-email-stokes-rumor-gravitational-waves-have-been-spotted)

Maybe.

(That's 3 solar masses of gravitational waves. LIGO wows: black holes heavy as 36+29 merge to 62 Suns + 3 Suns of gravitational waves (http://motls.blogspot.com/2016/02/ligo-wows-bh-masses-3629-to-62-suns-51.html?m=1))

schlaugh
2016-Feb-11, 01:12 PM
Even APOD is getting in on the act. The website shows a placeholder image until the LIGO presser at 11:00 EST. (Which means my post essentially self-destructs then.)

http://apod.nasa.gov/apod/astropix.html

Cougar
2016-Feb-11, 01:46 PM
RScience: ‘Woohoo!’ email stokes rumor that gravitational waves have been spotted (http://www.sciencemag.org/news/2016/02/woohoo-email-stokes-rumor-gravitational-waves-have-been-spotted)

Well, this is sounding more and more promising. A couple more hours and we'll know. What's the link for the press conference?

trinitree88
2016-Feb-11, 02:36 PM
Wasn't it only two or three years ago that people were getting exciting over neutrino's possibly travelling faster than light... Lets remember how that turned out !

Kevin1981. True, that some people were excited over that, but not all of them were..including myself. I've held steadfast that neutrinos and photons both travel at c and that both are massless, complying with the precepts of Special Relativity, and not violating it. They both have energy of E=hv...and momentum of hv/c. The issue of neutrino mass is that carried by the Particle Data Group, that any possible mass of a neutrino cannot exceeed the latest allowable limits of a few ev,...but that the possibility that they are still massless has not been ruled out yet.
The experiments which have shown that neutrinos can flavor switch from electron-type, to muon-type, to tau-type, have all been carried out in experiments involving pathways through matter. There the eigenstates of the neutrinos can superimpose on the matter eigenstates, allowing fluctuations to occur without the neutrinos themselves being required to be massive. .....(see MSW matter oscillations...) If they are, then they violate SR traveling at c.
As far as the gravitational waves go...the work of Guido Pizella @ Neutrino 88, Tufts University..showed that the Rome and Maryland bar gravitational-wave detectors, and the IMB, Mont Blanc, Kamiokande, and Baksan neutrino detectors were coincident @ 3.2 sigma...(Larry Suluk ,principal investigator of IMB @ talk @ MIT's Winter Course in Nuclear and Particle Physics 1991-2)...but the journals had switched to a requirement of 5 sigma...and disallowed it.) I never told him that the paper I wrote in April, 1982...predicting the coincidence of those two effects...that a change in the ambient neutrino flux would be seen in a sensitive gravimeter as a gravitational wave....and rewrote the paper which was submitted to Gravity Research Foundation, Babson College in their annual competition.
I did tell him that the "funny" distortion of the walkways in the IMB tunnels....where they would "bump up" in the middle....was likely the slow flow of the salt dome under the pressure of the overburden, and that eventually, on a geologic scale....the roof of their allegedly stable cavern would fall in. It did so in the IMB 3 months later. There had been an article in Scientific American on Salt Tectonics.
It was George Gamow, in his Harvard Project Physics Reader " Gravity" who said a neutrino/antineutrino pair could be a graviton....and the Z, the carrier of the neutral current can be any particle/antiparticle pair, so I coupled it to the Standard Model using Howard Georgi's article ,also in Sci. American, and made the prediction.
Seen @ 6 major International Labs....3.2 sigma. Supernova 1987a. pete

Grey
2016-Feb-11, 03:42 PM
Here (https://www.ligo.caltech.edu/detection)'s the short blurb, and here (http://www.ligo.org/news/detection-press-release.pdf)'s the full press release. Confirmed, gravitational waves from a black hole merger. Cool.

Cougar
2016-Feb-11, 04:43 PM
Here (https://www.ligo.caltech.edu/detection)'s the short blurb, and here (http://www.ligo.org/news/detection-press-release.pdf)'s the full press release. Confirmed, gravitational waves from a black hole merger. Cool.

Wow! It's not a rumor anymore.

trinitree88
2016-Feb-11, 04:50 PM
Here (https://www.ligo.caltech.edu/detection)'s the short blurb, and here (http://www.ligo.org/news/detection-press-release.pdf)'s the full press release. Confirmed, gravitational waves from a black hole merger. Cool.

Grey. That's cool indeed. I'll extend that confirmation to predict that a search of the neutrino detector database...IMB, SuperKamiokande, etc. will yield a 5 sigma coincidence of events with the timing of the seen BH merger. Betting a hot fudge sundae, three scoops, whip cream, and three cherries on top. pete

SRH
2016-Feb-11, 05:01 PM
Can someone please explain how they know the signal came from 2 merging black holes and not the Sun nor Earth?

Grey
2016-Feb-11, 05:17 PM
Grey. That's cool indeed. I'll extend that confirmation to predict that a search of the neutrino detector database...IMB, SuperKamiokande, etc. will yield a 5 sigma coincidence of events with the timing of the seen BH merger. Betting a hot fudge sundae, three scoops, whip cream, and three cherries on top. peteHmm, I think you're wrong that neutrionos have anything to do with mediating gravity, but I could also imagine that if those black holes had accretion disks, we might see some conventional particle interactions that could have produced a neutrino burst. Still, on the whole I think that's not too likely, so I'll take the bet. Should there be a time frame for it to be reported? Oh, and no cherries for me. I don't like Maraschino cherries.

But I also think you already owe me a hot fudge sundae from here (http://cosmoquest.org/forum/showthread.php?108431-Six-Questions-Physics-at-the-LHC&p=1803263#post1803263). It's been over five years, and I think that the astronomical community still doesn't know exactly what makes up the dark matter. I think most of them still expect it to be something non-baryonic, and at the very least there's certainly no consensus that it's all been somehow accounted for by normal baryonic matter, as you suggested would be the case.

And of course, there's this one (http://cosmoquest.org/forum/showthread.php?142253-Will-Dark-Matter-Finally-Reveal-Itself&p=2123009#post2123009) that still has seven years to go. I have a feeling that I might lose that one, because even if dark matter does turn out to be non-baryonic, it still might not be detected soon enough.

Grey
2016-Feb-11, 05:27 PM
Can someone please explain how they know the signal came from 2 merging black holes and not the Sun nor Earth?These kinds of detectors are unbelievably sensitive, so there's a fair amount of noise, not just from the Sun and the Earth, but from trucks driving by. That's why they have more than one detector, separated by a large distance. They can tell by the fact that they got the same signal on both that it's not anything local, and they can tell by the delay between when it arrived at one and the other the speed and direction that the signal had to be travelling, so that let's them easily rule out anything nearby. And by looking at the form of the signal itself (it's not just a big spike, it has a particular pattern including a frequency, changes in amplitude, a specific time scale, and so on), and comparing that to predictions from general relativity, they can tell a lot about the details of the interaction that had to produce it.

Something that would be exciting would be if this prompts building a couple more similar facilities. With more gravitational wave observatories(!) working together, we'd be able to get a pretty precise location for future events, and we could then take a look with optical and radio telescopes and see if we can see more detail.

Sticks
2016-Feb-11, 05:27 PM
Are there any such detectors outside of the US?

I hate to rain on the parade here, but if there are any LIGO detectors outside of the US, should they not have waited for independent confirmation of the results outside of the US before going public?

How many times have we had ground breaking discoveries announced, only for the claims to be retracted later because errors in the data came to light?

gzhpcu
2016-Feb-11, 05:32 PM
What are the implications for theoretical physics? Gravitons?

StupendousMan
2016-Feb-11, 05:33 PM
From the LIGO paper itself (which you can read for free at http://journals.aps.org/prl/pdf/10.1103/PhysRevLett.116.061102)


Only the LIGO detectors were observing at the time of
GW150914. The Virgo detector was being upgraded,
and GEO 600, though not sufficiently sensitive to detect
this event, was operating but not in observational
mode.

Grey
2016-Feb-11, 05:43 PM
Are there any such detectors outside of the US?To my knowledge, none with the sensitivity of the two LIGO facilities. Virgo, in Italy (which has worked closely with LIGO in the past and expects to do so in the future) is in the process of upgrading their equipment. There are other ongoing and proposed collaborations. So there's probably no way to corroborate this specific event, but it seems likely that there will be such for future events. Detection of gravitational waves pretty much requires having multiple separated facilities coordinating together, so they actually have agreements to share data and publish jointly.



I hate to rain on the parade here, but if there are any LIGO detectors outside of the US, should they not have waited for independent confirmation of the results outside of the US before going public?

How many times have we had ground breaking discoveries announced, only for the claims to be retracted later because errors in the data came to light?I think this is very different than, for example the OPERA experiment that seemed to point to superluminal neutrinos. In that case, the researchers more or less came forward and said they thought there was probably an error someplace, and were hoping the rest of the scientific community could help them track it down. I think this one looks solid.

Squink
2016-Feb-11, 05:45 PM
What are the implications for theoretical physics? Gravitons?

Perhaps we can measure how stiff spacetime is with respect to rapid fluctuations vs the usual long term steady-state.

Don Alexander
2016-Feb-11, 05:57 PM
It's incredible what they've managed to deduce from just one event!

- Full confirmation of the existence of gravitational waves
- Existence of binary black holes
- Strong upper limit on the mass of the Graviton
- Black holes in a peculiar mass range - these are quite heavy for stellar mass black holes

Grey
2016-Feb-11, 06:00 PM
What are the implications for theoretical physics? Gravitons?I don't think this gives anything either way on gravitons. Gravitational waves are a purely classical prediction from general relativity. So this confirms that prediction, and adds a new constraint to any hypothetical theory of quantum gravity, but doesn't specifically provide any evidence for or against such a quantum theory.

Fiery Phoenix
2016-Feb-11, 06:00 PM
Really amazing how Einstein continues to be right a full century later.

antoniseb
2016-Feb-11, 06:12 PM
Are there any such detectors outside of the US?...
People have mentioned Virgo, plus there is one being built in Japan that should come online in 2018, and some talk about building a new aLIGO site in India.

SRH
2016-Feb-11, 06:13 PM
I hope they accounted for solar flare interference...

http://www.spaceweather.com/images2016/08feb16/cosmicrays.png?PHPSESSID=0i18u43lko1tq47kpq90k0q6p 2

SRH
2016-Feb-11, 06:17 PM
That chart also matches up with the "about 4 detections" Sept 14 through January.

SRH
2016-Feb-11, 06:19 PM
Site detection separation was 7 milleseconds, btw

swampyankee
2016-Feb-11, 06:20 PM
Actually, I think this would be a lot different-- no one got that excited about the neutrinos that I know, we all pretty much expected the other shoe to drop. It was a very difficult measurement, and we had plenty of reason to doubt it was true. For gravitational waves, it's also a difficult measurement, but we have every reason to expect it is true-- due to binary pulsar data. No one was saying "if we don't detect superluminal neutrinos soon, we are badly mixed up about something"-- but that's just the situation with gravitational waves. We'd like to detect them, to show that physics works, but we'd also like to not detect them-- to show that there's more to know! So in a way, it's almost too much to hope that LIGO won't detect them.

I think part of the reason nobody got excited is that something was required for some sub-atomic decays, like neutron decay, n \Rightarrow p + \bar{\nu}, to satisfy conservation of momentum, which nobody wanted to give up, even at the subatomic level. It just took a long time to find it, the cost was modest relative to LIGO.

Don Alexander
2016-Feb-11, 06:37 PM
The one thing that puzzles me somewhat is the luminosity function of these events.

LIGO ran for roughly a decade and detected nothing.
ALIGO runs for, what, a week, and detects an event which according to Kip Thorne was not much below the sensitivity limit of LIGO.

And there's rumors that they've seen more. 4 of them so far, I hear. My best guess is that this has to do with the large volume increase, the "broadening of the horizon. 10-fold increase in detector sensitivity gets you ten times deeper into the Universe, but in terms of scannable volume, the increase is a 1000-fold.

Grey
2016-Feb-11, 06:55 PM
From the LIGO paper itself (which you can read for free at http://journals.aps.org/prl/pdf/10.1103/PhysRevLett.116.061102)Thanks, that's great to see. The graphs on page 2, comparing the actual strain data to a theoretical prediction from general relativity, are really very pretty.

Squink
2016-Feb-11, 07:25 PM
So, when's the announcement that ESA is moving up the launch date of eLISA (https://en.wikipedia.org/wiki/Evolved_Laser_Interferometer_Space_Antenna)?

Cougar
2016-Feb-11, 07:34 PM
From the LIGO paper itself (which you can read for free at http://journals.aps.org/prl/pdf/10.1103/PhysRevLett.116.061102)

What a paper! An instant classic.

Don Alexander
2016-Feb-11, 08:21 PM
Soon to be cited like a gazillion times.

I wonder why they published in PhysRevLett and not Science.

My best guess: Science would never have allowed open access to the paper.

Well, off to read it now.

Jens
2016-Feb-11, 08:22 PM
Grey. That's cool indeed. I'll extend that confirmation to predict that a search of the neutrino detector database...IMB, SuperKamiokande, etc. will yield a 5 sigma coincidence of events with the timing of the seen BH merger. Betting a hot fudge sundae, three scoops, whip cream, and three cherries on top. pete

That's certainly an interesting idea. In fact, since it was apparently a billion light years away, the arrival of a neutrino flux might give us an idea about the speed of neutrinos.

slang
2016-Feb-11, 08:32 PM
I'm at page 3 and already trying to visualize how enormously massive this event must be.. 70 solar masses worth of black hole rotating around each other 75 times per second in the space of the country I live in. And then merged in what looks to us to be half a second. Blink and you miss it.

Cougar
2016-Feb-11, 08:57 PM
I'm at page 3 and already trying to visualize how enormously massive this event must be....

An energy release (in gravitational waves) equivalent to about (200 solar masses * c2) per second! I guess that's how, after rippling through about a billion lightyears of space, we could still detect it. I wonder how the neighbors fared.

Don Alexander
2016-Feb-11, 09:56 PM
https://dcc.ligo.org/LIGO-P1500213/public
(https://dcc.ligo.org/LIGO-P1500213/public)
Here's the LIGO page for the paper. I also contains links to a bunch of other papers offering more details. All these papers are open access (at least in their LIGO preprint versions).

Anyway. Finished it.

Wow.

There's a special feeling to reading a paper that is likely to still be cited a hundred years from now, on the day it is published. The first of its kind, and all that. A moment of magnitude comparable to the 1919 report of how the Sun bent starlight following GR's rules, comparable to Hubble's discovery of the expanding Universe, to the discovery of the CMB... In this century, I guess only the Higgs boson compares.

Ken G
2016-Feb-11, 10:15 PM
Grey. That's cool indeed. I'll extend that confirmation to predict that a search of the neutrino detector database...IMB, SuperKamiokande, etc. will yield a 5 sigma coincidence of events with the timing of the seen BH merger. Betting a hot fudge sundae, three scoops, whip cream, and three cherries on top. peteI'll take that bet-- LIGO thinks the source is 1.3 billion light years away. Not gonna get neutrinos from that.

slang
2016-Feb-11, 10:29 PM
Did I understand correctly that they estimate this sort of thing happening once every few years in a supercluster of galaxies, or less?

antoniseb
2016-Feb-11, 10:45 PM
Did I understand correctly that they estimate this sort of thing happening once every few years in a supercluster of galaxies, or less?
Some rumors have indicated that three to five such events have been observed since September, the rumors haven't given quality of signal information about the others, but it appears this is a several times a year kind of event.

Fiery Phoenix
2016-Feb-11, 11:01 PM
I'll take that bet-- LIGO thinks the source is 1.3 billion light years away. Not gonna get neutrinos from that.
Why not?

antoniseb
2016-Feb-11, 11:13 PM
Why not?
Well, the idea is that there wouldn't be a high likelihood of one being detected from the event. This was perhaps 10,000 times as far away as SN1987A, which was the only event with any significant number of neutrinos detected, so it would need to have generated 100 Million times as many neutrinos to be detected in the same way ... but also, two merging black holes don't need to generate neutrinos anyway.

BioSci
2016-Feb-11, 11:16 PM
Biosci here, i have not posted for some time and have a question regarding LIGO.

In all the descriptions of how LIGO detects gravitational waves that I have seen, they talk about length changes (from the passing gravitational wave) resulting in changes in the time for the beams to traverse the instrument but I do not recall discussions regarding gravitational wave effects on time and how that may effect the speed of the laser beams.

Would such time effects add to or reduce the ability to detect length changes?

Thanks!

Biosci

slang
2016-Feb-11, 11:20 PM
Some rumors have indicated that three to five such events have been observed since September, the rumors haven't given quality of signal information about the others, but it appears this is a several times a year kind of event.

Wikipedia lists 8 superclusters as "near", and a twenty'ish more as "distant" with one at z=0.06. The paper says:


These observational results constrain the rate of stellarmass
binary black hole mergers in the local universe. Using
several different models of the underlying binary black hole
mass distribution, we obtain rate estimates ranging from
2–400 Gpc−3 yr−1 in the comoving frame

I think I read in one of the cited papers something like 1 Gpc-3 yr-1 as a high frequency estimate. Superclusers are OOM 100 million ly?

So putting together several tentative detections in a year, and 30'ish "local" superclusters... oh wait, I'm mixing parsecs and lightyears. Why is this so difficult, and not easy like computers? :)

Squink
2016-Feb-12, 02:51 AM
Site detection separation was 7 milleseconds, btw
Light, and presumably gravity, would travel 1260km in that time and distance (great circle) between the two detectors is about 3040 km. so they must have a fairly decent circle in the sky to look along. Perhaps we'll get lucky and someone will have pix of the afterglow.

selvaarchi
2016-Feb-12, 04:44 AM
India claims some credit in the detection of gravity waves.

http://www.business-standard.com/article/pti-stories/gravitational-waves-ind-institutes-pitched-in-with-research-116021200053_1.html


Indian scientists played a crucial role, including in-data analysis, in the path-breaking project for the detection of gravitational waves, or ripples in space-time, which Albert Einstein predicted a century ago.

Several institutes, including Institute of Plasma Research (IPR) Gandhinagar, Inter University Centre for Astronomy and Astrophysics (IUCAA), Pune, and Raja Ramanna Centre for Advanced Technology (RRCAT), Indore, were involved in the research.

The announcement of detection of gravitational waves was made simultaneously at IUCAA, Pune, and by scientists in Washington DC, USA.

Jerry
2016-Feb-12, 05:03 AM
India claims some credit in the detection of gravity waves.

http://www.business-standard.com/article/pti-stories/gravitational-waves-ind-institutes-pitched-in-with-research-116021200053_1.html

Very appropriate, given how much has been invested in this enormous project.

The clarity is stunning; and as Don intimated, eye opening in that the resolving power is only about a factor of five greater than the previous version of LIGO. This is such a clear signature that over-time (1-6 years) we should see many events; and quickly determined if this is an unexpected artifact.

- it sure looks like the real McCoy- .

Jerry
2016-Feb-12, 12:51 PM
I hope they accounted for solar flare interference...

http://www.spaceweather.com/images2016/08feb16/cosmicrays.png?PHPSESSID=0i18u43lko1tq47kpq90k0q6p 2

Wow. Check out the shape of the aurora waves on 15 September.

http://www.spaceweather.com/archive.php?view=1&day=15&month=09&year=2015

That is just what many would expect a pair of collapsing black holes to look like.

a1call
2016-Feb-12, 05:04 PM
So the gravitational waves exist.
What are the expectations regarding them?


* Would they penetrate matter undisturbed?
* Would they have different speeds in different media like electromagnetic waves?
* Would they refract or interfere wavelike?
* Would gravitational lensing bend their path?


Thanks in advance.

Grey
2016-Feb-12, 05:25 PM
* Would they penetrate matter undisturbed?There should be some interaction, but just like it takes enormous masses moving quickly to create measurable gravitational waves in the first place, it would similarly take a very large mass to have a noticeable effect on an existing wave.


* Would they have different speeds in different media like electromagnetic waves?I think the answer should be yes, but with the gravitational interaction so much weaker than the electromagnetic interaction, I think there would be very little difference between the "gravitational index of refraction" of empty space and that of anything but extremely dense objects. So, travelling through a neutron star might have some effect, but passing through the Earth would probably have an unmeasurably small effect.


* Would they refract or interfere wavelike?They should, but again, actually observing this would be a lot harder than just observing the waves in the first place. We usually observe refraction or interference by working with a continuous source of light and seeing how it changes, and it seems unlikely that we could find a source like that for gravitational waves.


* Would gravitational lensing bend their path?It should, since gravity curves spacetime, which affects everything travelling through it. Gravitational waves should be affected in the same way as light.

a1call
2016-Feb-12, 05:56 PM
Thank you very much Grey.

a1call
2016-Feb-12, 06:00 PM
Could we consider gravity a gravitational wave with a frequency of 0?
And expect it to behave as a gravitational wave with an infinitely low frequency?
Would all this explain the "Allais effect":



After analysis of Foucault pendulum data during the solar eclipse of July 11, 1991, L. Savrov suggested that the "pendulum responded to the remanent shock wave at the maximum of the total eclipse phase".[13]


https://en.m.wikipedia.org/wiki/Allais_effect


Or is the gravitational wave observed too weak to account for such anomalies?

Grey
2016-Feb-12, 06:15 PM
Could we consider gravity a gravitational wave with a frequency of 0?
And expect it to behave as a gravitational wave with an infinitely low frequency?
Would all this explain the "Allais effect":

Or is the gravitational wave observed too weak to account for such anomalies?Gravitational waves from the Earth-Sun system would be much too weak to measure without equipment that is orders of magnitude more sensitive than LIGO. Also, reading the Wikipedia article, it's not clear that the Allais Effect has been conclusively demonstrated to exist at all. So before we go looking for an explanation, we'd probably want to verify that there's something that needs explaining.

a1call
2016-Feb-12, 06:19 PM
Agreed. Thank you again for your replies Grey.

crosscountry
2016-Feb-12, 06:27 PM
Just want to join in and say how cool this detection is!

JCoyote
2016-Feb-12, 06:41 PM
An energy release (in gravitational waves) equivalent to about (200 solar masses * c2) per second! I guess that's how, after rippling through about a billion lightyears of space, we could still detect it. I wonder how the neighbors fared.

So I read ~3 solar masses of energy went into the wave. What are the effects on local matter, excluding peripheral EM radiation to the event?

What is the minimal safe radius for human-like life?

What is the chunky salsa radius?

Don Alexander
2016-Feb-12, 07:49 PM
It should, since gravity curves spacetime, which affects everything travelling through it. Gravitational waves should be affected in the same way as light.
The latter actually leads to an interesting thought: If the GW signal were lensed, would this lead to a higher mass estimation for the black holes?

On the other hand, if the redshift estimation is correct, lensing is very unlikely to have taken place, even if there were an intervening mass, the lensing would be small.

Cougar
2016-Feb-12, 08:16 PM
So I read ~3 solar masses of energy went into the wave.

Right, sorry. I was reading at page 7 of the paper - it's the peak gravitational wave luminosity that's equivalent to about 200 solar masses times c2 per second.


What are the effects on local matter, excluding peripheral EM radiation to the event?

What is the minimal safe radius for human-like life?

What is the chunky salsa radius?

All good questions. :) The wave "strength" has to drop off exponentially, I expect.

SRH
2016-Feb-12, 08:48 PM
Why would the merging of 2 black holes of approximately 70 solar masses in total only give a detectable signal in the last 0.5 seconds of the merger, and not for the 5 minutes before, or even 10,000 years before, and up to the merger?

How many times per second were these black holes spinning around each other, say 30 seconds before the merger?

antoniseb
2016-Feb-12, 09:45 PM
Why would the merging of 2 black holes of approximately 70 solar masses in total only give a detectable signal in the last 0.5 seconds of the merge...
It has to do with sensitivity of the detector and background noise. The final merger gives of a huge gravitational wave. The final orbits before the merger give off waves, but nothing so huge as the merger does.

SRH
2016-Feb-12, 10:34 PM
Is there anything comparable in the physical world?

For example, do 2 magnets spinning around each other have an exponentially large wavefront/bowshock in the EM field at the very end of their merger?

StupendousMan
2016-Feb-13, 12:26 AM
The wave "strength" has to drop off exponentially, I expect.

Actually, one of the weird things about gravitational waves is that our instruments respond to the AMPLITUDE of the waves, which falls off as (distance to the negative first power). The instruments which detect electromagnetic waves (and just about all other types of waves), on the other hand, respond to the INTENSITY of the waves, which falls off as (distance to the negative second power).

That makes it easier to detect gravitational wave sources which are very far away. If one source is 10 times farther than another, its signal in LIGO is just 0.1 times as strong; electromagnetic waves would be only 0.01 times as strong.

ngc3314
2016-Feb-13, 01:26 AM
Is there anything comparable in the physical world?

For example, do 2 magnets spinning around each other have an exponentially large wavefront/bowshock in the EM field at the very end of their merger?

The first thing that comes to my mind would be the annihilation of positronium, where the different charges of the electronic and positron allow a sort of inspiral before annihilation. The inspiral in this system is the classical approximation to a quantum behavior, but apparently valid for large excitation numbers (https://en.wikipedia.org/wiki/Talk%3APositronium). Jumps emitting EM radiation would become more frequent as the annihilation approaches, kind of sort of like a gravitational merger "chirp".

Don Alexander
2016-Feb-13, 01:48 AM
Anything before the last 0.2 seconds was too faint to be detected.

The measured frequency went from 35 Hz up to 250 Hz at merger time. No idea about 30 seconds earlier, though.

Squink
2016-Feb-13, 02:24 AM
Is there anything comparable in the physical world?Black holes are in the physical world.
However, spin a quarter on its edge, on a hard surface. It'll chirp at you before it lays down flat.

eburacum45
2016-Feb-13, 08:06 AM
I'm trying to understand how the LIGO wave detections give such interesting (and detailed) data. From a tiny wave detected in a very sensitive pair of instruments, they have a good idea of which direction it came from, how far away it is, and the (different) masses of the two holes. The paper has some lovely diagrams, but I can't quite see how they get from the raw data to the information published in the newspapers. What are the uncertainties in this process? Will we soon be seeing gravitational wave maps of the universe?

Sticks
2016-Feb-13, 09:23 AM
Plus I would like to see these observations repeated outside of the US in order to rule out possible false signals caused by local geography and geology. Are the detectors sufficiently far away from Yellowstone, which being a super volcano has a large magma chamber, which I understand causes local seismic activity.

The key to science is repeatability in other parts of the globe, and there have been incidents when people claimed a scientific breakthrough only for other labs to question the results. Does anyone remember Fleischmann–Pons claims of cold fusion?.

Now I must admit I have not been able to read the whole paper just in case these concerns have been addressed, but it would be nice to have these observations repeated elsewhere, just to be sure.

moozoo
2016-Feb-13, 10:11 AM
As I understand it, the observed gravitation waves exactly matched theoretical predictions.
Is there any scope to to detect things beyond general relativity?
i.e. if the detectors where much more sensitive could they detect details in the final stages of merger that existing theory can not?
eg the LHC discovered the higgs exactly as predicted but there are hopes it could detect something beyond the standard model.
Is this possible with super ligos?

I do realize that the ability to detect the numbers/frequency of many different types of events, and the possibility of discovering new events fully validates the need for gravity wave astronomy. I'm just wondering what possibilities exist to extend our theoretical knowledge other than confirming it.

slang
2016-Feb-13, 10:25 AM
I think that having two arms at each location may already give some clue to direction (by how the wave affects each arm), and having the two sites detect exactly the same signal, knowing it must reach the other one at light speed, must help even more in plotting general direction.


Plus I would like to see these observations repeated outside of the US

Yes, you said so on page 1. What does the nationality of the detector locations have to do with it? I assume you mean the general area rather than the country.


in order to rule out possible false signals caused by local geography and geology.

What is "local geology" when the sites are thousands of miles apart, one in Washington State near the Rockies, and one in Louisiana?


Are the detectors sufficiently far away from Yellowstone, which being a super volcano has a large magma chamber, which I understand causes local seismic activity.

It's tough to think of a way that Yellowstone can create a tremble that exactly matches the predicted signal for inspiralling black holes, including the ringout. But, since Yellowstone is much nearer to the Hanford site than the Livingston one, how could the exact same signal possibly be detected at both sites with only lightspeed travel times between them?


The key to science is repeatability in other parts of the globe, and there have been incidents when people claimed a scientific breakthrough only for other labs to question the results. Does anyone remember Fleischmann–Pons claims of cold fusion?.

Gravitational waves are not a new discovery, like cold fusion. There is already a Nobel prize awarded for proving providing strong evidence of their existence. IMHO this is more a technological breakthrough than a scientific one. A very significant milestone, sure.

selvaarchi
2016-Feb-13, 12:15 PM
Some more information on how international this project was. It has a 900-strong international team of researchers from 15 countries led by David Reitze, LIGO laboratory executive director. India has a sizable contribution with more than 59 people involved (in this project) with about 35 having direct involvement in this path-breaking detection event. This may be why there is a push to set up another LIGO (IndiGO) in India. The 3rd one will help with the precise location of the cosmic event that generated gravitational waves through triangulation. Good luck India, hope the Indian government gives the go ahead.

http://www.millenniumpost.in/NewsContent.aspx?NID=237253


Hundred years after Albert Einstein’s prediction of the presence of gravitational waves in his Theory of Relativity, a team of scientists from 15 countries led by David Reitze, LIGO laboratory executive director, announced their detection on Thursday, taking the world of physics to new exciting heights.

Working hard for over 30 years and surviving false alarms (such as the one in 2014 when scientists had announced it wrongly only to be later disproved), the 900-strong international team of researchers, including Indian scientists from the Inter-University Centre for Astronomy and Astrophysics and the Chennai Mathematical Institute, has confirmed the detection of gravitational waves by the twin Laser Interferometer Gravitational-Wave Observatory (LIGO) detectors located in Livingston, Louisiana, and Hanford, Washington.

The waves are extremely tiny, just millionth of an atom in size, but they open up before us exciting possibilities in the realm of space science and the Big Bang theory.

“It is one of the international projects with (the) biggest contingent of Indian scientists from nine labs and research institutions. More than 59 people are involved (in this project) with about 35 having direct involvement in this path-breaking detection event. The level of Indian participation shows the confidence we have gained in the international arena,” TV Venkateswaran, a scientist with Vigyan Prasar, told Down To Earth via email from Pune.

Sticks
2016-Feb-13, 12:53 PM
I assume you mean the general area rather than the country.

Yes that was what I was referring, if only in order to show that any regional issues, if any, have no bearing on the results.

Don Alexander
2016-Feb-13, 01:12 PM
Plus I would like to see these observations repeated outside of the US in order to rule out possible false signals caused by local geography and geology. Are the detectors sufficiently far away from Yellowstone, which being a super volcano has a large magma chamber, which I understand causes local seismic activity.

The key to science is repeatability in other parts of the globe, and there have been incidents when people claimed a scientific breakthrough only for other labs to question the results. Does anyone remember Fleischmann–Pons claims of cold fusion?.

Now I must admit I have not been able to read the whole paper just in case these concerns have been addressed, but it would be nice to have these observations repeated elsewhere, just to be sure.

Slang has already mentioned several aspects.

Of course they checked if anything conceivable except GWs would be able to create this signal. They found nothing. The detection system is extremely isolated from the rest of the Earth, but of course they still measure vibrations. The point is, they have hundreds of thousands of sensors spread across the array, which are designed to measure both noise contributors in a classical fashion (e.g., seismometers) as well as measure the integrity of the entire system. It's stated in the paper that any event which would be of "local" (Earth, Solar System) origin and powerful enough to create this signal would also have registered on some kind of other detector - and they saw nothing that was coincident.

The most likely cause - aside from a real GW event, of course - was a deliberate injection of a false signal. Something which actually happened in 2010 and was only revealed after the paper was complete and ready for submission. But unless they have Loki on their team, who is sniggering in his cubicle, this was not the case here.

StupendousMan
2016-Feb-13, 02:42 PM
I'm trying to understand how the LIGO wave detections give such interesting (and detailed) data. From a tiny wave detected in a very sensitive pair of instruments, they have a good idea of which direction it came from, how far away it is, and the (different) masses of the two holes. The paper has some lovely diagrams, but I can't quite see how they get from the raw data to the information published in the newspapers. What are the uncertainties in this process? Will we soon be seeing gravitational wave maps of the universe?

One answer to your question is the several different aspects of the detected wave signal: it's a periodic(ish) signal, in the first place. But the signal changes in two linked ways: first, the amplitude of the waves increases with time. Second, the frequency of the waves also increases with time. Third, those two changes occur in a particular manner, not independently. So, you may think of the signal from each LIGO site to have five properties: duration, average amplitude, average frequency, change-in-amplitude-with-time, and change-in-frequency-with-time.

On top of that, the signal was detected by two different LIGO devices separated by a large distance. The time delay between the two locations gives one very, very rough indication of the direction of the source. But there's an additional directional clue: the two LIGO instruments face in slightly different directions. The arms of the Louisiana LIGO do not lie in exactly the same plane as the arms of the Haverford LIGO. That means that a signal will (in most cases) appear slightly stronger at one site, whichever one happens to be oriented in a plane more nearly perpendicular to the direction of the source (in other words, a signal will be strongest when it comes from directly overhead).

So, putting those two different factors together, the LIGO team can get a rough, rough idea of the direction of the source. If a third detector, such as VIRGO, had seen the same signal, the direction would be better determined.

a1call
2016-Feb-13, 02:43 PM
Since/if GW travel at speed of light, has there been simultaneous collaborative visual/electromagnetic observations? If so has there been any lagging observed?

eburacum45
2016-Feb-13, 03:02 PM
One answer to your question is the several different aspects of the detected wave signal: it's a periodic(ish) signal, in the first place. (snip) Thanks for the answer. So the more LIGO-type detectors we have, the better the maps will be. Fascinating.

Don Alexander
2016-Feb-13, 03:05 PM
Since/if GW travel at speed of light, has there been simultaneous collaborative visual/electromagnetic observations? If so has there been any lagging observed?

The direction the signal came from is only a very rough location, about 600 deg^2. Nobody knows in exactly which galaxy this happened, so there are no specific observations of a possible optical counterpart.

http://arxiv.org/abs/1602.03868 Here's a paper on follow-up observations with the Swift satellite. I have not read it yet but don't expect them to yield any kind of viable information.

http://arxiv.org/abs/1404.5623 Leo Singer and colleagues did simulations on the error regions and the possibility of EM follow-up.

One big "problem" with the merger of two black holes is that such an event emits nothing but GWs - as far as I know, it does not couple into the electroweak sector at all. This is in contrast to a merger between neutron stars or a BH-NS merger, where a short gamma-ray burst might be expected (though I'm unsure about the co-detectability, GRBs are emitted along the polar axis while GWs are, it seems, mostly emitted into the equitorial plane).

slang
2016-Feb-13, 03:13 PM
Since/if GW travel at speed of light, has there been simultaneous collaborative visual/electromagnetic observations?

This I have been wondering about as well. SWIFT doesn't list a GRB on 14 september 2015, at least I don't see anything. Might SWIFT not seeing anything mean something, or was it just looking in the wrong direction?

ETA: simulposted, thanks for those links and explanation.

antoniseb
2016-Feb-13, 03:18 PM
The direction the signal came from is only a very rough location, about 600 deg^2. Nobody knows in exactly which galaxy this happened, so there are no specific observations of a possible optical counterpart....
Once there is a third detector on Earth (VIRGO later this year), sources positions will be able to be narrowed significantly, but to really get down to identifying individual galaxies we might need multiple detectors in solar orbit. This sort of thing seems to be at least 20-30 years away, possibly longer if budgets don't increase, or if it turns out there will seldom be a coincident source to study in some other spectrum (as Don Alexander notes in #77 above).

slang
2016-Feb-13, 03:40 PM
http://arxiv.org/abs/1602.03868 Here's a paper on follow-up observations with the Swift satellite. I have not read it yet but don't expect them to yield any kind of viable information.

They received a report 45 hours after the event, but did not find anything. 4.7 square degrees were observed in this after-search. During the event Swift was indeed looking the other way.


The XRT observations covered 4.7 square degrees, and contained
2% of the probability from the final ‘LALInterence’
ALIGO error region (8% if this is convolved with the
GWGC). However, Abbott et al. (2016) reported that the
most likely source of the GW event is a binary black-hole
trigger at 500 Mpc. Since the GWGC only extends to 100
Mpc and the coalescence of two stellar mass black holes is
not expected to produce EM radiation, our lack of detection
is not surprising.

They add that they've shown being able to act quickly upon receiving the report, and software is being updated on Swift to allow for a better search after GW triggers.

Sticks
2016-Feb-13, 05:06 PM
Slang has already mentioned several aspects.

Of course they checked if anything conceivable except GWs would be able to create this signal. They found nothing. The detection system is extremely isolated from the rest of the Earth, but of course they still measure vibrations. The point is, they have hundreds of thousands of sensors spread across the array, which are designed to measure both noise contributors in a classical fashion (e.g., seismometers) as well as measure the integrity of the entire system. It's stated in the paper that any event which would be of "local" (Earth, Solar System) origin and powerful enough to create this signal would also have registered on some kind of other detector - and they saw nothing that was coincident.

The most likely cause - aside from a real GW event, of course - was a deliberate injection of a false signal. Something which actually happened in 2010 and was only revealed after the paper was complete and ready for submission. But unless they have Loki on their team, who is sniggering in his cubicle, this was not the case here.

Thanks for that, it is just that on other things we have had false dawns before, so one tends fall into the habit of to treating announcements now with an abundance of caution.

a1call
2016-Feb-13, 05:25 PM
Apologies for going off the deep end, but are there any theoretical/hypothetical means of man-made generation of ripples in the fabric of spacetime?
Could this be an artificial signal?
https://en.m.wikipedia.org/wiki/Hydrogen_line#Possible_uses_for_SETI

WaxRubiks
2016-Feb-13, 06:04 PM
I was thinking it could be an alien warp drive. :p

Grey
2016-Feb-13, 06:07 PM
Thanks for the answer. So the more LIGO-type detectors we have, the better the maps will be. Fascinating.Yes, my hope is that this discovery will provide encouragement for funding to support continued research, including bringing new facilities on line so that we can do this kind of analysis.

Squink
2016-Feb-13, 06:07 PM
a1call, being able to detect something is often the first step in being able to make changes to that something.
That said, don't get your hopes up.

antoniseb
2016-Feb-13, 06:21 PM
Apologies for going off the deep end, but are there any theoretical/hypothetical means of man-made generation of ripples in the fabric of spacetime?
Could this be an artificial signal? ...
Considering we are seeing several such signals per year from a volume of space that is about ten octillion cubic light years, and that a predicted natural phenomenon could create what was observed, and the message is merely one chirp, I'd say it is a fairly poor means of communication, and unlikely that anyone put the effort into trying to recreate it artificially. At the moment, we don't know of a way to imitate this, but it is possible that our understanding of the science of strong gravity and gravitational waves will improve from these observations as we get better at seeing them.

a1call
2016-Feb-13, 06:45 PM
...the message is merely one chirp, I'd say it is a fairly poor means of communication, and unlikely that anyone put the effort into trying to recreate it artificially.
That's a very good point.
Thank you for all the replies.

Don Alexander
2016-Feb-13, 07:02 PM
Apologies for going off the deep end, but are there any theoretical/hypothetical means of man-made generation of ripples in the fabric of spacetime?
You typing your message sent out gravitational waves.

Yes, my hope is that this discovery will provide encouragement for funding to support continued research, including bringing new facilities on line so that we can do this kind of analysis.
The e-LISA team probaby celebrated really hard. I liked Thorne's somewhat snide comments at the press conference concerning NASA getting out f the LISA prtnership back in '11.

slang
2016-Feb-13, 09:27 PM
Here's a link to the actual press conference announcing the discovery. It's a little over an hour long video, and about half of it is the presentation, the rest is Q&A.

The Announcement: LIGO detects gravitational waves -- Press Conference (https://www.youtube.com/watch?v=vy5vDtviIz0)

I think most of the information in it is already covered here, either in posts or in the linked paper, but for some this may be easier to follow.

pindo
2016-Feb-14, 02:11 AM
So that's what those funny sensations have been.

Don Alexander
2016-Feb-14, 03:01 PM
I'm just looking at the paper by Phil Evans on Swift follow-up of GW150914.

There, I found something which made me wonder. Then wonder more. Then get really angry!!!

The paper states:

"This event was announced to the EM follow-up partners on 2015 September 16 at 06:39 UT (Singer 2015)."

An actual reference? What may this be?

I find:

"Singer L., 2015, GRB Coordinates Network, 18330"

A GCN? Weird. I don't seem to remember that...

(Just in case you do not know: GCNs are "Gamma-ray burst Coordinate Network circulars, usually used to send short messages concerning GRBs. Discovery of GRBs, afterglow follow-up etc. The system is an e-mail list you have to sign up to if you want to send and receive them, but aside from that, it is - supposed to be! - completely public, GCNs are - supposedly - immediately listed at: http://gcn.gsfc.nasa.gov/gcn3_archive.html Usually faster than they land in your inbox. I myself work in the field of GRBs and receive these things regularly.)

I go to look on the GCN page. I find:

18374 GRB 151001B: Swift detection of a burst
18373 GRB 151001A: Swift detection of a burst with an optical
counterpart
18369 GRB 150925A: Swift/UVOT Upper Limits
18368 GRB 150925A: Swift-BAT refined analysis
18367 GRB 150925A: Swift-XRT refined Analysis
18366 GRB 150925A: Enhanced Swift-XRT position
18365 GRB 150925A: Swift detection of a burst
18360 Konus-Wind observation of GRB 150922A
18358 GRB 150922A: Fermi GBM observation
18357 IPN Triangulation of GRB 150922A (short/hard)
18356 Konus-Wind observation of GRB 150919A
18355 IPN Triangulation of GRB 150919A (short / hard)
18352 ANTARES neutrino detection: Fermi GBM Observations
18351 Fermi GBM trigger bn150920977 is not due to a GRB
18329 GRB 150915A: Swift-XRT refined Analysis
18328 GRB 150915A, Swift-BAT refined analysis

18330-50? Completely missing. Further holes further up, then it seems to return to normal. 18397 is missing too, though... And 858, which I found due to this page:
https://dcc.ligo.org/LIGO-P1500227/public
which is the ONLY hit you get from Google on "GCN 18330".

I then went to my GCN folder in my mail program. Not there either.

So it seems we have a SECRET GCN SYSTEM sending out GW-related GCNs (a system which is supposed to be totally public, and everything, iirc) to the SELECT FEW.

Hooray.

I feel this is, at the very least, a strong misuse of the GCN system.

Squink
2016-Feb-14, 04:11 PM
It did seem like an event Swift should've picked up.

slang
2016-Feb-14, 04:18 PM
I'm just looking at the paper by Phil Evans on Swift follow-up of GW150914.

There, I found something which made me wonder. Then wonder more. Then get really angry!!!

Noo... I want the quiet, patient, scholarly Don Alexander, not raging Gamma Ray Zombie Alexander!

It got me thinking though. Could it be that the system supports different kinds of messages? Off to find the description of the system. After discarding many hits on the other GCN network that interests me (Global Cycling Network (https://www.youtube.com/user/globalcyclingnetwork), a great youtube channel for cycling enthousiasts), I found the technical description (http://gcn.gsfc.nasa.gov/gcn_describe.html) of the GRB Coordinates Network. It mentions that for notices, there are filtering conditions:


"The Notices are the result of information received by GCN/TAN in real-time, processed into a standard format and automatically distributed to the those people wishing to receive specific Notices (based on a variety of filtering conditions)."

Those filtering conditions seem to be described in chapter 4 (http://gcn.gsfc.nasa.gov/gcn_describe.html#tc8). This notice 18330 doesn't really report a GRB like the Swift ones, does it? Is it possible that you have filtered this one out in your subscription (http://gcn.gsfc.nasa.gov/config_builder.html)? I'd subscribe myself to test it but it seems they want a lot of things to set this up.


It did seem like an event Swift should've picked up.

Nope... 1) Swift was looking the other way. 2) Probably no EM emission from BH mergers. See previous page and the papers Don Alexander linked.

Don Alexander
2016-Feb-14, 04:54 PM
Those filtering conditions seem to be described in chapter 4 (http://gcn.gsfc.nasa.gov/gcn_describe.html#tc8). This notice 18330 doesn't really report a GRB like the Swift ones, does it? Is it possible that you have filtered this one out in your subscription (http://gcn.gsfc.nasa.gov/config_builder.html)?
No, it has nothing to do with that.

a) I have contacted several other people who have all confirmed to me that a secret subsystem within the GCN was set up for only those people who signed a memorandum with the ALIGO team.
b) Whatever my subscription details are, they would have no impact on the normal public posting of GCNs. These GCNs do not exist. At least not right now. Perhaps they will be included on the public page later.

Look, I get that large collaborations should have internal mailing lists to discuss their results before publication. It's not like I'm complaining that I'm not receiving news on the newest results from CERN. ;) But, like I said this seems a misuse of a system that is the antithesis of "secret society".

Grey
2016-Feb-14, 04:59 PM
Grey. That's cool indeed. I'll extend that confirmation to predict that a search of the neutrino detector database...IMB, SuperKamiokande, etc. will yield a 5 sigma coincidence of events with the timing of the seen BH merger. Betting a hot fudge sundae, three scoops, whip cream, and three cherries on top. peteI think Ken G and I win this one. Here (http://icecube.wisc.edu/news/view/398)'s a report from IceCube. It looks like one of the first things they did at IceCube and ANTARES was to look for coincident neutrinos (they were alerted immediately by the LIGO team, long before the public announcement). They didn't find any.

slang
2016-Feb-14, 05:41 PM
b) Whatever my subscription details are, they would have no impact on the normal public posting of GCNs.

That's what I figured right after I posted, and I couldn't find it anywhere either. Oh well, I learned some more about how GCN works, technically. :)

I can understand the embargo nature of the first ALIGO results. Whether the GCN network should or should not be used to carry messages that are not publicly available is a management issue, not technical, therefore *slang yawns* :)

Don Alexander
2016-Feb-14, 06:28 PM
I think Ken G and I win this one. Here (http://icecube.wisc.edu/news/view/398)'s a report from IceCube. It looks like one of the first things they did at IceCube and ANTARES was to look for coincident neutrinos (they were alerted immediately by the LIGO team, long before the public announcement). They didn't find any.
"How to make an already long author list way longer" 101

Total pages: 14
Author list and affiliations: 9
Actual science: 5

Results: 0 :P

Have fun with your fudge sunday. Can't for the life of me imagine why anyone wuld think we'd detect neutrinos from such a source when there, seemingly, no detections even nearby SNe, like 2014J in M82 (okay, that was a Ia, I think they don't emit as many neutrinos as core-collapse SNe) and SN 2016adj in Centaurus A, bot roughly 100 times closer than this GW event.

StupendousMan
2016-Feb-14, 07:06 PM
No, it has nothing to do with that.

a) I have contacted several other people who have all confirmed to me that a secret subsystem within the GCN was set up for only those people who signed a memorandum with the ALIGO team.
b) Whatever my subscription details are, they would have no impact on the normal public posting of GCNs. These GCNs do not exist. At least not right now. Perhaps they will be included on the public page later.

Look, I get that large collaborations should have internal mailing lists to discuss their results before publication. It's not like I'm complaining that I'm not receiving news on the newest results from CERN. ;) But, like I said this seems a misuse of a system that is the antithesis of "secret society".

I agree with you. Have you asked the leaders of GCN why they agreed to set up this secret channel?

ngc3314
2016-Feb-15, 01:53 AM
I think Ken G and I win this one. Here (http://icecube.wisc.edu/news/view/398)'s a report from IceCube. It looks like one of the first things they did at IceCube and ANTARES was to look for coincident neutrinos (they were alerted immediately by the LIGO team, long before the public announcement). They didn't find any.

Once it could be told, the colleague in the next office was telling me about the paper reporting the IceCube and ANTARES neutrino limits at the time. The paper's authors included the IcuCube, ANTARES, and LIGO teams. Between listing them and giving the mandated acknowledgments for various funding sources, she said that it took 21 pages to give a 3-page description of the limits and how they were obtained. Science today. Fortunately, having gone to electronic-only versions of the journals meant that even short communications no longer have strict page limits.

Squink
2016-Feb-17, 08:00 PM
Data in a nice format: http://heasarc.gsfc.nasa.gov/docs/objects/heapow/archive/special/GW150914_LIGO.html

Staticman
2016-Feb-18, 11:59 PM
Plus I would like to see these observations repeated outside of the US in order to rule out possible false signals caused by local geography and geology. Are the detectors sufficiently far away from Yellowstone, which being a super volcano has a large magma chamber, which I understand causes local seismic activity.

The key to science is repeatability in other parts of the globe, and there have been incidents when people claimed a scientific breakthrough only for other labs to question the results. Does anyone remember Fleischmann–Pons claims of cold fusion?.

Now I must admit I have not been able to read the whole paper just in case these concerns have been addressed, but it would be nice to have these observations repeated elsewhere, just to be sure.


Slang has already mentioned several aspects.

Of course they checked if anything conceivable except GWs would be able to create this signal. They found nothing. The detection system is extremely isolated from the rest of the Earth, but of course they still measure vibrations. The point is, they have hundreds of thousands of sensors spread across the array, which are designed to measure both noise contributors in a classical fashion (e.g., seismometers) as well as measure the integrity of the entire system. It's stated in the paper that any event which would be of "local" (Earth, Solar System) origin and powerful enough to create this signal would also have registered on some kind of other detector - and they saw nothing that was coincident.

The most likely cause - aside from a real GW event, of course - was a deliberate injection of a false signal. Something which actually happened in 2010 and was only revealed after the paper was complete and ready for submission. But unless they have Loki on their team, who is sniggering in his cubicle, this was not the case here.

I share not only the excitement for the finding but also some of Sticks' concerns. It would really be a shame that something like BICEP2 announcement happened again just for rushing things more than prudence in science demands. Also the press conference looked more like a movie commercial than a serious science announcement(compare with Atlas and CMS in the Higgs case).
But to refer to Don Alexander's reply. I think the announcement would have benefited from a more through discussion of possible non-GW signals mimicking gravitational waves. I read the pertinent papers by aLIGO on the correlated transients and more specifically on the detectors, the physical environment monitor(PEM) sensors. One can obtain information from these also at pem.ligo.org.
My conclusion from going through the sensors and the info in the aLIGO technical papers from my experience in geophysics is that the claim that "they checked if anything conceivable except GWs would be able to create this signal" is athe very least overstated. I'll concentrate on electromagnetic contamination. The sensors listed on the papers consist basically of RF receivers at fixed frequencies of 9 and 45 MHz to cover issues with possible couplings with the interferometer devices that are explained in the technical paper "Characterization of transient noise in Advanced LIGO relevant to gravitational wave signal", and 3-axis fluxgate magnetometers in the range 0-900 Hz to explore the local magnetic fields(they mention Schumann resonances for instance as possible sources of contamination near the GW waves frequencies searched (30-300 Hz). That is all.
Now I would have expected more sensors dedicated to EM sub-radio detection(VLF waves above 1 KHz) but they don't mention any antennas with those specifications. The reason is that the enormous senitivity achieved by Advanced LIGO interferometers (remember it detects strains h(t) of 1e10-22) should make it capable of coupling to the radiation pressure of sub-radio EM waves of the appropriate power in that frequency range. Besides the Schumann resonances commented above they acknowldege solar radio flares as sources of EM audio-band waves in the range of the GWs frequencies discarding them at the moment of the detection, but it is well known in the field of geophysics and atmospheric electrodynamics that there are a large number of possible sources of sub-radio waves in the ELF-VLF bands besides lightning and solar winds, specifically EM radiation transients derived from seismic movement that is analyzed routinely when watching for earthquakes. It is also not impossible for powerful enough sub-radio waves like those emitted by magnetars to slip through the ionosphere. Such signals would also give a correlated detection in both aLIGO interferometers. And all these wouldn't be detected just with magnetometers if the sources frequencies weren't in the range of the magnetometers.
So I wonder if the work on discarding spurious environment sources and detections was as complete as it should have been to make such bold claims.

Jens
2016-Feb-19, 06:14 AM
18330-50? Completely missing. Further holes further up, then it seems to return to normal. 18397 is missing too, though... And 858, which I found due to this page:
https://dcc.ligo.org/LIGO-P1500227/public
which is the ONLY hit you get from Google on "GCN 18330".


On the plus side, consider this: I have heard rumors that there have been three more detections of gravitational waves since the one that was reported on Feb. 11. So perhaps you can find when they were by finding the gaps in the GCN system!

Jens
2016-Feb-19, 06:22 AM
Plus I would like to see these observations repeated outside of the US in order to rule out possible false signals caused by local geography and geology. Are the detectors sufficiently far away from Yellowstone, which being a super volcano has a large magma chamber, which I understand causes local seismic activity.

There will be a few more detectors available in the future, for example KAGRA in Japan (which I was lucky enough to be able to see (under construction) last year). In any case, though, the signals are quite far apart, and apparently the pattern that they saw is consistent with what they should have seen for merging black holes. I was initially skeptical as well during the press conference, but it seems pretty solid. Also, seismic waves move at the speed of sound in the material, so unless the activity was exactly in the middle of the two locations, you wouldn't see them happening simultaneously. That's why you can give warning of earthquakes, because it takes some time for the waves to propagate. But gravitational waves happen at the speed of light, so will always be seen more or less simultaneously.

Don Alexander
2016-Feb-26, 04:15 PM
On the plus side, consider this: I have heard rumors that there have been three more detections of gravitational waves since the one that was reported on Feb. 11. So perhaps you can find when they were by finding the gaps in the GCN system!
Indeed! A source of mine informed me about just this oversight. They told of an event roughly a month after GW150914 which turned out to be a false signal - not injected, but just very low signal-to-noise, and a revised anylsis then showed it to be a noise event. Furthermore, I was pointed to "look at the region of GCN 18725 or so...".

Here are my findings:

18329: exists, posted on 150917
Missing: 18330-18350, 18353,4, 18359, 18361-18364, 18370.18372, 18388, 18390, 18394,5, 18397, 18418, 18420, 18424


18441: exists, posted on 151022
Missing: 18442,3, 18445,6, 18451, 18453-18455, 18457,8, 18460, 18470,1, 18473,4, 18476,7, 18486, 18488,9, 18494, 18497,8, 18500, 18528, 18536, 18547, 18553, 18557, 18561,2, 18563, 18566, 18569, 18572,3, 18584, 18621, 18626, 18655, 18690, 18709


18727: exists, posted on 151227
Missing: 18728-18730, 18732-18735, 18737,8, 18740-18742, 18744, 18748, 18759, 18762-18764, 18768, 18771, 18774-18776, 18779,80, 18782, 18784, 18786, 18789-18791, 18800, 18803,4, 18806,7, 18809,10, 18811-18813, 18822, 18824, 18833, 18834,35, 18840, 18842,3


18845: exists, posted on 160109
Missing: 18846-18851, 18853, 18858, 18868, 18870, 18873, 18889, 18903, 18914, 18937, 19005, 19017, 19021,22, 19034, 19048, 19055

While the ~160107/8/9 event is relatively close to the Christmas one, the sudden hole of 6 GCNs in a row smells like another GW detection. So it looks like GW150914, GW1510~20 was false, and then we have two more real events (likely).

Don Alexander
2016-Mar-01, 12:19 PM
http://arxiv.org/abs/1602.08492

The EM follow-up paper is out. 1500 authors describe... hardly anything. :P

Anyway, the paper is interesting inasmuch as it cites almost all GCNs linked to GW150914, and also gives minor details as to what they contain. Out of the first block mentioned above, only four GCNs are not cited, though it seems highly likely they also deal with GW150914, since they are randomly distributed amongst the list. Many further GCNs in the next three blocks also deal with GW150914.

On the other hand, the six-consecutive-GCNs block in eearly January has nothing to do with GW150914. So it might indeed be a third (real?) event.

Squink
2016-Mar-01, 01:20 PM
Data mining? ;)

Don Alexander
2016-Mar-05, 12:02 AM
http://gcn.gsfc.nasa.gov/other/GW150914.gcn3

Now available to me and everyone else.

01101001
2016-Apr-19, 02:03 AM
Gamma-Ray Burst Detected Near Gravitational Wave Source (http://news.discovery.com/space/astronomy/gamma-ray-burst-detected-near-gravitational-wave-source-160418.htm)


NASA’s Fermi Gamma-ray Space Telescope detected the very weak and brief burst of high-energy X-rays, consistent with a short gamma-ray burst (or GRB), less than half a second after LIGO registered GW150914.

WaxRubiks
2016-Apr-19, 11:22 AM
Gamma-Ray Burst Detected Near Gravitational Wave Source (http://news.discovery.com/space/astronomy/gamma-ray-burst-detected-near-gravitational-wave-source-160418.htm)

could this be evidence that black holes, ie with event horizons, don't actually form, and that the matter in the BH is not within an event horizon, and can still release gamma rays?

01101001
2016-Apr-19, 02:36 PM
From the cited news story: NASA Press Release: NASA's Fermi Telescope Poised to Pin Down Gravitational Wave Sources (http://www.nasa.gov/feature/goddard/2016/nasas-fermi-telescope-poised-to-pin-down-gravitational-wave-sources)


Black hole mergers were not expected to emit significant X-ray or gamma-ray signals because orbiting gas is needed to generate light. Theorists expected any gas around binary black holes would have been swept up long before their final plunge. For this reason, some astronomers view the GBM burst as most likely a coincidence and unrelated to GW150914. Others have developed alternative scenarios where merging black holes could create observable gamma-ray emission. It will take further detections to clarify what really happens when black holes collide.

Stay tuned.

George
2016-Apr-19, 05:16 PM
could this be evidence that black holes, ie with event horizons, don't actually form, and that the matter in the BH is not within an event horizon, and can still release gamma rays?

Since gamma rays are produced by the annihilation of neutrinos and antineutrinos, and these are likely produced (and separated before annihilation) at event horizons, which are static, what happens when your EH becomes extremely dynamic, including a bounce back and forth due to the mass loss from the gravity wave? [I hope to see a Hawking hey-day on this one.]

WaxRubiks
2016-Apr-19, 05:20 PM
[I hope to see a Hawking hey-day on this one.]does Hawking believe in event horizons at the moment?

crosscountry
2016-Apr-19, 05:34 PM
Isn't there a spot near the center of mass of a dual BH system where the net gravity is close to zero? In this place couldn't EM radiation pass through unimpeded?

George
2016-Apr-19, 07:38 PM
does Hawking believe in event horizons at the moment? Apparently. (pun intended) He has proposed apparent horizons, I think he calls them. I don't understand the distinctions between the two and I am not sure one precludes the other, though they might.

George
2016-Apr-19, 07:40 PM
Isn't there a spot near the center of mass of a dual BH system where the net gravity is close to zero? In this place couldn't EM radiation pass through unimpeded?The EH no longer is spherical as the two become closer. The EH formed, however, would not open any windows.

crosscountry
2016-Apr-19, 09:46 PM
that's once they are too close, but prior to that there will be a substantial time when they are still distant enough to form a saddle point of gravity, where an observer (or light) would be pulled in neither direction.

Grey
2016-Apr-20, 01:13 PM
Since gamma rays are produced by the annihilation of neutrinos and antineutrinos, and these are likely produced (and separated before annihilation) at event horizons...Gamma rays aren't produced by neutrino annihilations. Neutrinos don't generally annihilate (they have a fantastically low cross section even with normal matter, the neutrino-antineutrino cross section would be astonishingly low), and even if they did, neutrinos don't interact via the electromagnetic force, so they can't produce gamma rays directly as a result. There are some ways that a neutrino can produce electromagnetic radiation via secondary effects, but it's always when interacting with normal matter. You can have gamma rays from electron-positron annihilation, or proton-antiproton annihilation, or the like, but not from neutrinos.

George
2016-Apr-20, 01:33 PM
Gamma rays aren't produced by neutrino annihilations. Neutrinos don't generally annihilate (they have a fantastically low cross section even with normal matter, the neutrino-antineutrino cross section would be astonishingly low), and even if they did, neutrinos don't interact via the electromagnetic force, so they can't produce gamma rays directly as a result. There are some ways that a neutrino can produce electromagnetic radiation via secondary effects, but it's always when interacting with normal matter. You can have gamma rays from electron-positron annihilation, or proton-antiproton annihilation, or the like, but not from neutrinos.Perhaps it is different, however, for super events. This paper (http://cds.cern.ch/record/549082/files/0204081.pdf) seems to suggest this may be the case: "[3] Subsequent annihilations of neutrinos and antineutrinos purportedly lead to gamma-ray bursts".

Grey
2016-Apr-20, 07:58 PM
Perhaps it is different, however, for super events. This paper (http://cds.cern.ch/record/549082/files/0204081.pdf) seems to suggest this may be the case: "[3] Subsequent annihilations of neutrinos and antineutrinos purportedly lead to gamma-ray bursts".Interesting. Following up on the reference there (BLACK HOLE – NEUTRON STAR MERGERS AS CENTRAL ENGINES OF GAMMA-RAY BURSTS, section 4.2 (http://arxiv.org/pdf/astro-ph/9908290.pdf)), it looks like the neutrinos and antineutrinos annihilate to produce electrons and positrons, and those deposit energy, heating up the surrounding matter, and then producing thermal gamma rays. So they are indeed proposing an indirect path. I'd think they would do that just by interacting with the surrounding material directly (as the paper also notes, high density neutron matter is not transparent to neutrinos). But I'll acknowledge that the paper authors probably know more about this than I do. ;)

George
2016-Apr-20, 09:34 PM
Interesting. Following up on the reference there (BLACK HOLE – NEUTRON STAR MERGERS AS CENTRAL ENGINES OF GAMMA-RAY BURSTS, section 4.2 (http://arxiv.org/pdf/astro-ph/9908290.pdf)), it looks like the neutrinos and antineutrinos annihilate to produce electrons and positrons, and those deposit energy, heating up the surrounding matter, and then producing thermal gamma rays. So they are indeed proposing an indirect path. I'd think they would do that just by interacting with the surrounding material directly (as the paper also notes, high density neutron matter is not transparent to neutrinos). But I'll acknowledge that the paper authors probably know more about this than I do. ;)
Well, you understand it better than I do. It would be cool to see a strong hypothesis showing that the tremendous jolt of the merger, shoveing the EH to ~ 4x its size (surface area) in a near instant, would produce a flood of particles and a GRB! We have measured the thunder, but I want the lightning too. :)

Grey
2016-Apr-21, 12:49 PM
Well, you understand it better than I do. It would be cool to see a strong hypothesis showing that the tremendous jolt of the merger, shoveing the EH to ~ 4x its size (surface area) in a near instant, would produce a flood of particles and a GRB! We have measured the thunder, but I want the lightning too. :)I think that we probably need more observations to be able to really understand all the details. For that, we probably need a couple more gravitational wave observatories, so that we can pinpoint these events accurately enough that we can then bring optical and radio telescopes to bear. The good news is, it sounds like LIGO's success is making that prospect pretty likely, but the bad news is, it will take time to build those facilities and bring them online.

antoniseb
2016-Apr-21, 01:10 PM
We aren't getting public information on new GW events, but I suspect four or five of them have been seen since the 14 Sept 2015 event, but it won't be really interesting until VIRGO comes on line so they can triangulate the positions of the events.

George
2016-Apr-21, 02:35 PM
Yes, are we not on another precipice of astronomical wonders? :) Great stuff!!

Don Alexander
2016-Jun-06, 04:51 PM
Welp, looks like that alleged GRB linked to GW150914 was just noise...

http://arxiv.org/abs/1606.00314

(And just in case someone asks: The authors of this article actually are part of the Fermi GBM team. It seems they did an independent analysis, came to contrasting conclusions, and finally decided to withdraw from the Connaughton paper.)

crosscountry
2016-Jun-06, 06:58 PM
I think this is a very telling sentence



Our conclusion is more consistent with the expectation of no γ-ray emission from binary black hole mergers (Lyutikov 2016), and requires no effort in significant fine-tuning of models to explain the alleged delay of the gamma-ray emission relative to the gravitational wave emission.

WaxRubiks
2016-Jun-06, 07:29 PM
Welp, looks like that alleged GRB linked to GW150914 was just noise...

http://arxiv.org/abs/1606.00314

(And just in case someone asks: The authors of this article actually are part of the Fermi GBM team. It seems they did an independent analysis, came to contrasting conclusions, and finally decided to withdraw from the Connaughton paper.)

that's a shame. I was hoping that the GRB was evidence that BHs don't have event horizons.

Ken G
2016-Jun-07, 09:51 PM
Welp, looks like that alleged GRB linked to GW150914 was just noise...So I was right. Now we'll see if my skepticism about planet 9 is as justified as my skepticism about the gamma rays.

George
2016-Jun-09, 06:06 PM
So I was right. You might be right is the conclusion. Are we not working with a data set of one? How positive are they in applying their false positives view to this unique case, especially given the timing circumstance in this instance?

Care to bet me a sundae on it?? :) I say grbs will be found with bh mergers > 50 solar masses. We've felt the thunder; lightning will be found, too. ;) [I know. Think hyperbole more than good analogy.]

Ken G
2016-Jun-10, 02:24 AM
You might be right is the conclusion. What I mean is I was right to be skeptical. We never get to know what's right in some absolute sense! We could see ten gravitational wave detections with no gamma rays, and then improve our detection threshhold and see gamma rays. I just mean, the marginal character of the detection was suspicious-- it was a huge coincidence that both would be barely above threshhold, with two totally different measurements. So that triggered my "B-S" meter.

George
2016-Jun-11, 11:57 PM
What I mean is I was right to be skeptical. I blame love for my over-reaction -- ice cream love. :)

Don Alexander
2016-Jun-15, 11:06 AM
https://news.mit.edu/2016/wednesday-ligo-virgo-scientists-discuss-continued-search-gravitational-waves-aas-meeting

News is coming up!!!!

antoniseb
2016-Jun-15, 12:42 PM
https://news.mit.edu/2016/wednesday-ligo-virgo-scientists-discuss-continued-search-gravitational-waves-aas-meeting

News is coming up!!!!
Thanks Don Alexander! I'm looking forward to what they say, even if it is simply an upcoming date that VIRGO will start listening, and be able to triangulate the sky position of the sources. It would be a plus if they tell us how many other events have been observed since September.

01101001
2016-Jun-15, 04:03 PM
Prognostication (lifted wholly from an article that may have jumped the embargo): another event 2015 December 26.

01101001
2016-Jun-15, 05:17 PM
Webcast live, 10:15 AM PDT: https://iframe.dacast.com/b/59062/c/268750

01101001
2016-Jun-15, 05:22 PM
Nature: LIGO detects whispers of another black-hole merger (http://www.nature.com/news/ligo-detects-whispers-of-another-black-hole-merger-1.20093)


The detailed analysis of this second detection confirmed that the signature had to be the ripples from a pair of black holes. This time, the signal from the gravitational waves lasted one full second, instead of one-fifth of a second as in the first event. The second event encompassed the objects’ last 27 orbits around each other, versus just five or so from the first detection. This enabled the researchers to get a test of general relativity that was in some respects twice as precise as their test during the first detection.

StupendousMan
2016-Jun-15, 06:03 PM
Link to the paper describing the new event in Physical Review Letters:

http://journals.aps.org/prl/pdf/10.1103/PhysRevLett.116.241103

Cougar
2016-Jun-15, 07:04 PM
Nature: LIGO detects whispers of another black-hole merger (http://www.nature.com/news/ligo-detects-whispers-of-another-black-hole-merger-1.20093)

No time to read now. Thanks for the brief detail. Excellent!

WaxRubiks
2016-Jun-15, 07:14 PM
is there any gamma ray burst associated with this?

StupendousMan
2016-Jun-15, 07:25 PM
No. If there had been, it would have been included in the press conference, since it would have been much bigger news than a second GW detection alone.

The discovery paper does not provide the details needed to answer "why not?" However, I'd put lots of money on the speculation that the signal was noticed only days or, more probably, weeks after it happened (that's part I), and there was again a gigantic area on the sky inside which the signal might have originated (part II).

Don Alexander
2016-Jun-15, 08:31 PM
Prognostication (lifted wholly from an article that may have jumped the embargo): another event 2015 December 26.

See my post #104 in this thread! :D

Here's another big paper that appeared today:

https://dcc.ligo.org/public/0124/P1600088/015/bbh-o1.pdf

Edit: Seems I was wrong about a fourth event on about the 9th of January, though. If I understand the PRL paper, these three are "full disclosure". Three, because the one from October, which I was told was just noise, seems to be real after all, but the significance is still quite low.

George
2016-Jun-15, 09:54 PM
is there any gamma ray burst associated with this? Perhaps something will emerge with time. No doubt some are on the hunt for a timely gamma ray detection.

This event involved much smaller blackholes and at a slightly greater distance. Gamma rays, if they are shown to be associated with mergers, suffer from the inverse square law with distance, whereas the GW decreases only in a linear manner with distance.

Jens
2016-Jun-16, 12:19 AM
Prognostication (lifted wholly from an article that may have jumped the embargo): another event 2015 December 26.

There might be things I don't fully understand, but the APS has a clear anti-embargo policy (https://www.aps.org/publications/apsnews/200008/viewpoint-chodos.cfm). The researchers might have tried to impose one themselves I guess.

01101001
2016-Jun-16, 01:02 AM
Press Kit, 228th AAS Meeting, San Diego, CA, 12-16 June 2016 (https://aas.org/media-press/embargo-policy-aas-division-meetings)


All findings are embargoed until the time of presentation at the meeting. "Time of presentation" means the start time of the oral or poster session in which the paper will be given, or the start time of the corresponding press conference (if any), whichever comes first. See the complete AAS embargo policy for more information.

Don Alexander
2016-Jun-16, 01:13 AM
Perhaps something will emerge with time. No doubt some are on the hunt for a timely gamma ray detection.

"With time" being NOW and the answer is still no:

http://arxiv.org/abs/1606.04901

Three further papers on EM follow-up are out on astro-ph:

http://arxiv.org/abs/1606.04538
http://arxiv.org/abs/1606.04574
http://arxiv.org/abs/1606.04795

Their gist essentially seems to be: "Hey, look at these nice SNe we found while wild-goose-chasing something which doesn't exist!"

StupendousMan
2016-Jun-16, 12:58 PM
No. If there had been, it would have been included in the press conference, since it would have been much bigger news than a second GW detection alone.

The discovery paper does not provide the details needed to answer "why not?" However, I'd put lots of money on the speculation that the signal was noticed only days or, more probably, weeks after it happened (that's part I), and there was again a gigantic area on the sky inside which the signal might have originated (part II).

It's a good thing I did NOT put "lots of money" on my claim. While it is true that the area of the sky to be searched was "gigantic", I wasn't right about the delay in finding the signal: the papers mentioned by Don in the previous post state that an alert was sent out to astronomers 38 hours after the waves reached LIGO. So, more than one day, but probably not "days", and certainly not "weeks."

Don Alexander
2016-Jun-16, 02:14 PM
There might be things I don't fully understand, but the APS has a clear anti-embargo policy (https://www.aps.org/publications/apsnews/200008/viewpoint-chodos.cfm). The researchers might have tried to impose one themselves I guess.

This is highly ironic considering these GW events have been among the most secretive things I've ever seen...

George
2016-Jun-16, 05:46 PM
"With time" being NOW and the answer is still no:Likely no is not no.

http://arxiv.org/abs/1606.04901 -- They seem more reluctant with "no", though your odds seem favorable.
"Ultimately, a statistically large sample of well-observed localization probability maps for BBH mergers will be needed to confidently say whether GW150914-GBM is associated with a BBH merger."

http://arxiv.org/abs/1606.04538 -- This is with a much small merger and, I think, slightly farther away.
"We report the results of a Dark Energy Camera (DECam) optical follow-up of the gravitational wave (GW) event GW151226."

http://arxiv.org/abs/1606.04574
"Given the uncertain EM signature of the true counterpart, it is uncertain as to what will be the key diagnostic to set it apart from a long list of unrelated candidates."

I suppose that the lack of a viable theoretical model to explain a GBM would certainly add doubt to one, but my hope is that this is new territory for discovery, and since it is a violent son-of-a-gun, perhaps something exciting (including GBMs) will emerge. Time will tell. Care to bet a Sundae?

What was enjoyable to learn in the recent presentation is that these events happen on average about every 15 minutes! Wow. When younger, I could oscillate myself in any size swimming pool (given vertical side walls) so that white-caps formed within minutes. The serenity of space seems a little less serene and a little more like those pools. [Perhaps I oscillated a few cycles too many. ;)]

Don Alexander
2016-Jun-16, 07:23 PM
What's a "GBM"?

GBM is the Gamma-Ray Burst Monitor on Fermi.

Do you mean a GRB?

And my answer concerned specifically the detection a GRB coincident with the two new events. The new Fermi paper shows that none were detected.

George
2016-Jun-16, 07:50 PM
What's a "GBM"?

GBM is the Gamma-Ray Burst Monitor on Fermi.

Do you mean a GRB? Yes, I meant GRB. Thanks.


And my answer concerned specifically the detection a GRB coincident with the two new events. The new Fermi paper shows that none were detected. Ah, that helps. The hope I have is for GRBs with GW150914 class events, assuming both of the others are indeed smaller mass mergers.

Don Alexander
2016-Jun-16, 08:59 PM
Earlier, I received a GCN concerning XMM-Newton slew observations which passed over the GW151226 localization region. This seems to imply that the Memorium of Understanding has run out, and any GW-related results will appear immediately and publicly on the GCN system.

All results for the two new were posted yesterday, and it seems this was it for O1. There simply can't be any new events until the start of O2 later in the summer.

I also found out my prediction for a fourth event in early January was wrong, this strong cluster of six secret GCNs was indeed a fluke - it seems it dealt mainly with one supernova that had been discovered. Have not gotten around to reading those yet.

WaxRubiks
2016-Jun-16, 09:28 PM
could it be that a GRB may only be emitted in a certain direction from the black hole merger? And so not always detectable.?

Squink
2016-Jun-17, 01:52 AM
https://upload.wikimedia.org/wikipedia/commons/d/db/LIGO_measurement_of_gravitational_waves.svg
There's really no drift in the baseline at all, is there?
Space is a lot more slippery than water.

01101001
2016-Jun-17, 02:24 AM
could it be that a GRB may only be emitted in a certain direction from the black hole merger? And so not always detectable.?

Polar gamma-rays versus equatorial gravitational waves, I expect.

That, and also gamma-rays may not issue from black-hole mergers, so then directions would not matter.

George
2016-Jun-17, 02:19 PM
could it be that a GRB may only be emitted in a certain direction from the black hole merger? And so not always detectable.? I don't think there are any models that address GRBs in BH mergers. An accretion disk of some kind would be a good candidate to generate GRBs but disks should not be there normally. [Neutron star mergers, however, with another NS or BH may have some disk material and may produce a GRB, if my cursory read of one paper is correct.]

Models, however, will soon emerge, no doubt, if GRBs are associated with certain BH mergers. Current models, as I understand it, demonstrate GWs will be produced but with no EM. Suggesting gamma rays or other EM will result from BH mergers is only shooting-from-the-hip wild speculation. That's what I'm doing. I'm intrigued with whatever else is going on with mergers besides a nice little multi-solar mass energy GW. [I am an amateur, so take what I say accordingly.]

Don Alexander
2016-Jun-17, 04:56 PM
I don't think there are any models that address GRBs in BH mergers.
Actually, far off the mark:
http://adsabs.harvard.edu/cgi-bin/nph-ref_query?bibcode=2016arXiv160203920C&refs=CITATIONS&db_key=PRE
That's the list of all papers citing the Connaughton paper on the possible GW150914 GBM event. You'll find multiple papers eschewing models to produce such a short GRB_ 2016ApJ...821L..18P (http://adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2016ApJ...821L..18P&db_key=AST&link_type=ABSTRACT), 2016arXiv160302848M (http://adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2016arXiv160302848M&db_key=PRE&link_type=ABSTRACT), 2016ApJ...819L..21L (http://adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2016ApJ...819L..21L&db_key=AST&link_type=ABSTRACT)... As well as a bunch of papers either refuting the GBM detection, or stating that their should be NO EM emission.

An accretion disk of some kind would be a good candidate to generate GRBs but disks should not be there normally. [Neutron star mergers, however, with another NS or BH may have some disk material and may produce a GRB, if my cursory read of one paper is correct.]
Considering BH/NS and NS/NS mergers are THE prime candidate progenitor system for short GRBs, your cursory rwad is indeed correct. And short GRBs will most definitely produce GWs. They are just much fainter than when two whopping 30 M_sol BHs merge.

George
2016-Jun-17, 07:17 PM
Actually, far off the mark:
http://adsabs.harvard.edu/cgi-bin/nph-ref_query?bibcode=2016arXiv160203920C&refs=CITATIONS&db_key=PRE
That's the list of all papers citing the Connaughton paper on the possible GW150914 GBM event. You'll find multiple papers eschewing models to produce such a short GRB_ 2016ApJ...821L..18P (http://adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2016ApJ...821L..18P&db_key=AST&link_type=ABSTRACT), 2016arXiv160302848M (http://adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2016arXiv160302848M&db_key=PRE&link_type=ABSTRACT), 2016ApJ...819L..21L (http://adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2016ApJ...819L..21L&db_key=AST&link_type=ABSTRACT)... As well as a bunch of papers either refuting the GBM detection, or stating that their should be NO EM emission. That's helpful. These papers address GRBs from accretion disk activity, one involving a supermassive BH. I'm not surprised to see papers on this. What would surprise me is a paper suggesting a GRB emission during a BH/BH (and no supermassive ones) merger with no accretion disk. It's my understanding that it's deemed more likely that BH binaries will not have disks. Is this correct?


.... And short GRBs will most definitely produce GWs. [I assume you mean BH mergers will produce the GWs.]


They are just much fainter than when two whopping 30 M_sol BHs merge. The inverse square law takes its toll on GRBs, especially at > billion light years.

Don Alexander
2016-Jun-17, 10:33 PM
That's helpful. These papers address GRBs from accretion disk activity, one involving a supermassive BH. I'm not surprised to see papers on this. What would surprise me is a paper suggesting a GRB emission during a BH/BH (and no supermassive ones) merger with no accretion disk. It's my understanding that it's deemed more likely that BH binaries will not have disks. Is this correct?
Yes. It's expected that the accretion disk(s) will be either accreted or blown away during the inspiral process. The merger is supposed to happen in a hard vacuum.

Bing Zhang submitted a paper where he postulated that if one the black holes was charged, the final inspiral could create leptonic jets and an EM signal. Others pointed out that the amount of charge necessary for this process was completely unrealistic.

[I assume you mean BH mergers will produce the GWs.]
No, not really. For me "short GRB" automatically implies a BH-NS or NS-NS --> BH merger. Therefore, I am most definitely not speaking of BH-BH mergers.

The inverse square law takes its toll on GRBs, especially at > billion light years.
Well, GW wave amplitude decreases linearly, it seems. Problem is, the masses involved in such a short GRB are way smaller than in GW150914 - maybe just 2 + 2 M

George
2016-Jun-18, 03:03 PM
Is there any BH/BH mass distribution estimate? If these happen every ~ 15 minutes, then how often will the large mass mergers be detectable? It already looks like many per year will be found, especially with the new improvements.

Strange
2016-Jun-18, 04:39 PM
Some estimates from the original observation here: https://cplberry.com/2016/02/23/gw150914-the-papers/#rates
I assume this has been updated with the latest results, but I haven't looked for details.

George
2016-Jun-20, 02:43 PM
Some estimates from the original observation here: https://cplberry.com/2016/02/23/gw150914-the-papers/#rates
I assume this has been updated with the latest results, but I haven't looked for details.

Looks like the next run, O2, should improve the count significantly (perhaps 4x or 5x), followed by perhaps a 3-fold or more increase for O3, if I'm reading their probability chart correctly, which is a bit confusing for me.

Your link has a link to the LIGO newsletter (http://www.ligo.org/magazine/LIGO-magazine-issue-8.pdf#page=8). [Their comic-book presentation (pg. 20) of the discovery process is a hoot!] This newsletter has a link (http://arxiv.org/pdf/1602.03842v2.pdf) giving an estimate for a BBH (Binary Black Hole) merger rate of 2 to 600 Gpc-3yr-1, as stated in the abstract. No doubt this will get tweaked soon enough.

Strange
2016-Jun-20, 09:17 PM
More entertaining comics here: http://antimatterwebcomics.com/comic/how-many-people-did-you-lie-to/

George
2016-Jun-22, 04:52 PM
More entertaining comics here: http://antimatterwebcomics.com/comic/how-many-people-did-you-lie-to/

Yep, and it was the "I'm lying to my Mom" that tickled me the most.

selvaarchi
2016-Sep-18, 12:59 AM
It is less then a year since we detected gravitation waves but no news from the front has come out recently. Just came across this video which covers "What gravitational waves haven't told us yet". Sharing it and hoping when the other LIGO detectors come on stream in the next decade we will go into a new age of astronomy like Galileo opened up the current age of astronomy.

https://www.youtube.com/watch?v=4ef6KJ7vfIw


Published on Aug 26, 2016

A scientist and professor, Dr. Sanjit Mitra has done considerable research in ‘Efficient analysis algorithms for Gravitational Waves and Cosmology’.
His talk gives us an insight into the unexplored applications of gravitational waves- ideas we probably weren’t aware of!

Ken G
2016-Sep-18, 11:44 AM
Yet what's a little unconvincing about his analogy to Galileo opening up a new window on the cosmos is that Galileo ground some glass and stuck together an object in his house, it probably took him a few months and the equivalent of maybe a thousand dollars, max. And even that was just to develop it-- he could no doubt eventually whip them out much faster and cheaper. Imagine if it instead required a hundred million dollars and the efforts of a huge scientific community to develop a single telescope, which was justified simply to prove that light does indeed come from space? Had they done that, would they have been justified in saying that the new discovery would open up a new window on space? We can't even get a telescope funded that is capable of seeing the formation of the first stars, and that is the same kind of extrapolation of Galileo's telescope, starting from something that cheap, that Mitra is talking about doing for gravitational wave astronomy. I just don't see it-- most of the motivation was in proving that the waves exist, it was never motivated as a new form of astronomy. It's true that there is a whole spectrum of gravitational waves we have not yet seen, which could tell us a lot about all kinds of objects that looking at light only tells us so much. But there's a bunch of mundane telescopes that could also tell us all kinds of things about those objects, that we cannot get funded right now! Look at how much the building of JWST has stalled astronomical funding for other projects, and that's a relatively straightforward extrapolation of Galileo's cheap little home-built instrument.

So I don't think it's fair to expect gravitational wave astronomy to do much more than pick off the low-hanging fruit, for quite some time. Given the cost problem, that's what Mitra would need to be able to show-- not that it is possible to do it, but that it is cost effective to do it.

selvaarchi
2016-Sep-18, 12:17 PM
Yet what's a little unconvincing about his analogy to Galileo opening up a new window on the cosmos is that Galileo ground some glass and stuck together an object in his house, it probably took him a few months and the equivalent of maybe a thousand dollars, max. And even that was just to develop it-- he could no doubt eventually whip them out much faster and cheaper. Imagine if it instead required a hundred million dollars and the efforts of a huge scientific community to develop a single telescope, which was justified simply to prove that light does indeed come from space? Had they done that, would they have been justified in saying that the new discovery would open up a new window on space? We can't even get a telescope funded that is capable of seeing the formation of the first stars, and that is the same kind of extrapolation of Galileo's telescope, starting from something that cheap, that Mitra is talking about doing for gravitational wave astronomy. I just don't see it-- most of the motivation was in proving that the waves exist, it was never motivated as a new form of astronomy. It's true that there is a whole spectrum of gravitational waves we have not yet seen, which could tell us a lot about all kinds of objects that looking at light only tells us so much. But there's a bunch of mundane telescopes that could also tell us all kinds of things about those objects, that we cannot get funded right now! Look at how much the building of JWST has stalled astronomical funding for other projects, and that's a relatively straightforward extrapolation of Galileo's cheap little home-built instrument.

So I don't think it's fair to expect gravitational wave astronomy to do much more than pick off the low-hanging fruit, for quite some time. Given the cost problem, that's what Mitra would need to be able to show-- not that it is possible to do it, but that it is cost effective to do it.
Do not agree with your view that not much will happen in this area. Europe, India and China have already plans to build one each. So we will go from 2 in USA to 5 in the world in 10 years time. China also announced they plan to have one that is based in outer space.

Sent from my SM-G900F using Tapatalk

Ken G
2016-Sep-22, 03:47 PM
Do not agree with your view that not much will happen in this area. Europe, India and China have already plans to build one each. So we will go from 2 in USA to 5 in the world in 10 years time. China also announced they plan to have one that is based in outer space.

Sent from my SM-G900F using TapatalkI never said not much more will happen! What I did say is that the claims being made that gravitational astronomy is analogous to Galileo's telescope opening up a new window on the universe require ignoring some very basic truths about cost/benefit analyses.

George
2016-Sep-22, 04:00 PM
Yet what's a little unconvincing about his analogy to Galileo opening up a new window on the cosmos is that Galileo ground some glass and stuck together an object in his house, it probably took him a few months and the equivalent of maybe a thousand dollars, max. According to Galileo, in one account I read, he did it in one day from the time he heard of Lippershey's spy glass, who was headed to Venice to market it. He had to work fast and he was smart enough to reason to use both the convex and concave combination, giving him an upright image vs. Lippershey's (though he may or may not have known of the inverted image of Lippershey). It wouldn't surprise me if he took several days given the use of embellishments by him. He made one to be a beautiful scope & case and elected to give it to the City of Venice (resulting in a nice benefit the came to him by the city thereafter). All of this supports further your analogy, of course.

Ken G
2016-Sep-23, 06:46 AM
Yes, even the neutrino detecting facilities, which are cheaper and had an easier time getting the first detection than did gravitational waves, never claimed that neutrino astronomy was the next thing after optical telescopes! Neutrino astronomy has had some impressive successes, like discovering neutrino oscillations and verifying some basic supernovae processes, but it's not like we have mapped the sky, discovered new classes of objects, and altered the Big Bang story the way Mitra is insinuating that gravitational waves are going to do (if we will only dump a significant chunk of our gross national product into). He's just trying to stimulate some excitement, so we can grant him some poetic license, but there's quite a bit of hyperbole mixed in with that science!

George
2016-Sep-23, 03:11 PM
Yes, neutrino astronomy would seem to be a great comparison. Optical has significant advantages because of its shorter wavelength, abundance, atmospheric window, and, especially, its spectroscopy benefits. It is incredible what optical astronomy has wrought! Not even Zeus would have come close in prognostication.

Of course, if we are very lucky, perhaps a large bread crumb will be gleaned from gravity waves such that space will be seen anew and we can cut the 325 years of travel time to p-Centauri at 100x our fastest craft (Juno @ 87,000 mph). How great it would be to paraphrase J. McGee...

Oh! I have slipped the surly bonds of earth,
And danced among the stars on laughter-silvered wings;
Starward I’ve climbed, and joined the tumbling mirth
Of colored nebulous clouds, -- and done a hundred things
You have not dreamed of – Wheeled and soared and swung
Far into the starlit silence of space.

selvaarchi
2016-Oct-04, 01:35 PM
After opting out of playing a significant role in ESA's planned space-based facility to detect gravitational waves, NASA is now considering taking a 20% stake in it.

http://www.spacepolicyonline.com/news/nasa-resumes-gravitational-wave-tech-development-to-partner-with-esa


NASA has decided to resume technology development for a space-based facility to detect gravitational waves in cooperation with the European Space Agency (ESA). ESA is planning to launch such a mission in the 2030s. Funding constraints led NASA to curtail planning for a Laser Interferometer Space Antenna (LISA) earlier this decade and its role in ESA's mission was expected to be minor, but dramatic advances in the field have altered the landscape. A recent report from the National Academies recommended that NASA reconsider its role and the agency has done just that.

Paul Hertz, Director of NASA's Astrophysics Division in the Science Mission Directorate, told a NASA Advisory Council (NAC) subcommittee yesterday that the agency has agreed to increase its participation in ESA's L3 gravitational wave mission to 20 percent, the maximum ESA will allow. The L3 mission is expected to be launched in 2033 or 2034. Over that period of time, Hertz said, NASA will spend approximately $300-350 million.

George
2016-Oct-04, 09:10 PM
L3?

selvaarchi
2016-Oct-04, 09:34 PM
L3?

More information on ESA's L3 gravitational wave mission (http://sci.esa.int/cosmic-vision/57910-goat-final-report-on-the-esa-l3-gravitational-wave-mission/).

George
2016-Oct-06, 05:03 PM
It's still unclear, though I only glanced at the 71 pages.

They do show an illustration of three satellites offset from the Sun-Earth line by 22 deg.. These will rotate once per year, keeping them siderally aligned, obviously. Very interesting! There seems to be a follow-up mission (GRACE) planned for L1 (Sun). The paper does not have the word Lunar or Moon, but L3 is a lunar reference, right?

Shaula
2016-Oct-07, 02:51 AM
The paper does not have the word Lunar or Moon, but L3 is a lunar reference, right?
No, it is Large Mission Number 3. L1 is JUICE (JUpiter ICy moons Explorer), L2 is Athena (Advanced Telescope for High-ENergy Astrophysics). There are also M and S (Medium and Small) class missions.

George
2016-Oct-07, 01:52 PM
LIB! (Well I'll be...) Thanks, Shaula, for the deconflation.

Ken G
2016-Oct-07, 02:23 PM
Just wait until they decide to have an L1 mission to the L2 point, that won't confuse anyone....

George
2016-Oct-07, 09:10 PM
Just wait until they decide to have an L1 mission to the L2 point, that won't confuse anyone....Someone must be a big ZZ Top fan to use a LaGrange point for a mission name.

But I am still confused about the 22 deg. trailing mission position. Is it stable over there?

21786

[I don't know why I have two images with only one "ATTACH"]

crosscountry
2016-Dec-09, 06:10 PM
Here is a very fantastic podcast with Dr. Reitze who ran the LIGO project. It's in two parts.

https://www.listentospacepod.com/episodes/2016/10/9/66-the-most-ambitious-measurement-ever-made-with-dr-reitze-part-1
https://www.listentospacepod.com/episodes/2016/10/16/67-the-most-ambitious-measurement-ever-made-with-dr-reitze-part-2

publiusr
2016-Dec-09, 08:20 PM
Ow, stubbed my toe on a Weber bar.

George
2016-Dec-10, 07:56 PM
Here is a very fantastic podcast with Dr. Reitze who ran the LIGO project. It's in two parts.

https://www.listentospacepod.com/episodes/2016/10/9/66-the-most-ambitious-measurement-ever-made-with-dr-reitze-part-1
https://www.listentospacepod.com/episodes/2016/10/16/67-the-most-ambitious-measurement-ever-made-with-dr-reitze-part-2
Wow! Great explanation of LIGO's design and operation. Sort of pico technology on giant steroids.

I do need to find that beer. :)

01101001
2017-Aug-24, 12:48 AM
Old topic, new rumbling.

New Scientist:
Exclusive: We may have detected a new kind of gravitational wave (https://www.newscientist.com/article/2144937-exclusive-we-may-have-detected-a-new-kind-of-gravitational-wave/amp/)


Over the weekend, astronomer J. Craig Wheeler of the University of Texas at Austin launched speculation over a potential new LIGO detection by tweeting: “New LIGO. Source with optical counterpart. Blow your sox off!”

Colliding neutron stars?

WaxRubiks
2017-Aug-24, 01:12 AM
presumably the merger of two neutron stars would result in a black hole...?

01101001
2017-Aug-24, 01:32 AM
Forbes: Beyond Black Holes: Could LIGO Have Detected Merging Neutron Stars For The First Time? (https://www.forbes.com/sites/startswithabang/2017/08/23/beyond-black-holes-could-ligo-have-detected-merging-neutron-stars-for-the-first-time/)


Because neutron stars are less massive but physically larger, the gravitational wave signals they emit are lower in amplitude and occur over longer periods. However, the signal is extremely predictable over much longer periods of time than previous mergers show: for many seconds, minutes, or even hours, unlike the fraction-of-a-second signals for massive black holes. It means that we need to be significantly closer to neutron stars than black holes to see them merge: hundreds of millions of light years at most, at least with the current LIGO/VIRGO setup. We can detect them, but we need to be roughly ten times closer to get the same amplitude signal that we've seen from black holes.

Ken G
2017-Aug-24, 02:50 AM
Anything that increases the possible number of sources would be very helpful-- the current limits of LIGO have suffered from a pretty poor source rate! If neutron star mergers can also be detected, then perhaps the planned upgrades to LIGO will gather additional justification.

01101001
2017-Aug-24, 05:26 AM
presumably the merger of two neutron stars would result in a black hole...?

You first need to presume the resulting combined mass is sufficient.

Wikipedia: Stellar collision :: Neutron star collisions (https://en.wikipedia.org/wiki/Stellar_collision#Neutron_star_collisions)

WaxRubiks
2017-Aug-24, 05:51 AM
You first need to presume the resulting combined mass is sufficient.

Wikipedia: Stellar collision :: Neutron star collisions (https://en.wikipedia.org/wiki/Stellar_collision#Neutron_star_collisions)

I just assumed that as neutron stars were so close to the limit that two of them would automatically be above the limit, as long as no mass was shed.



Neutron star collisions




Video showing the simulated collision of two neutron stars


Neutron star collisions occur in a fashion similar to the rare brand of Type Ia supernovae (https://en.wikipedia.org/wiki/Type_Ia_supernova) resulting from collisions. When two neutron stars (https://en.wikipedia.org/wiki/Neutron_star) orbit each other closely, they spiral inward as time passes due to gravitational radiation. When the two neutron stars meet, their collision leads to the formation of a black hole (https://en.wikipedia.org/wiki/Black_hole) (assuming their combined mass exceeds the Tolman–Oppenheimer–Volkoff limit (https://en.wikipedia.org/wiki/Tolman%E2%80%93Oppenheimer%E2%80%93Volkoff_limit)) . This creates a magnetic field that is trillions of times stronger than that of Earth, in a matter of one or two milliseconds. Astronomers believe that this event is what creates certain kinds of gamma-ray bursts (https://en.wikipedia.org/wiki/Gamma-ray_burst).[7] (https://en.wikipedia.org/wiki/Stellar_collision#cite_note-7)

So maybe the picked up a gamma-ray-burst.

01101001
2017-Aug-24, 08:12 PM
Nature: Rumours swell over new kind of gravitational-wave sighting (http://www.nature.com/news/rumours-swell-over-new-kind-of-gravitational-wave-sighting-1.22482)


An hour later, astronomer Peter Yoachim, at the University of Washington in Seattle, tweeted that LIGO had seen a signal with an optical counterpart (i.e. something that telescopes could see) from the galaxy NGC 4993, which is around 40 million parsecs (130 million light years) distant in the southern constellation Hydra. “Merging neutron-neutron star is the initial call”, he followed up.
[...]
Astronomers who do not want to be identified say that NASA’s Fermi Gamma-ray Space Telescope is rumoured to have spotted γ-rays emerging from the same region of sky as the potential gravitational-wave source — gossip which a senior Fermi member declined to comment on.

Brief end-of-run announcement Friday about any candidate events, likely no details until data analyzed.

01101001
2017-Aug-24, 10:18 PM
I just assumed that as neutron stars were so close to the limit that two of them would automatically be above the limit, as long as no mass was shed.

By the way...

Nature (http://www.nature.com/news/rumours-swell-over-new-kind-of-gravitational-wave-sighting-1.22482)


Details of the gravitational waves at the time of the collision and in the following instants could also reveal information about the structure of neutron stars — which is largely unknown — and whether their merger resulted again in a neutron star or in the formation of a new black hole.

slang
2017-Aug-24, 11:27 PM
Thanks. I guess if it pans out as hoped for, it'll nicely shore up the analysis of the earlier sources too.

01101001
2017-Aug-25, 02:47 PM
As expected, nothing official.

LIGO Scientific Collaboration News (http://www.ligo.org/news.php)


A VERY EXCITING LIGO-VIRGO OBSERVING RUN IS DRAWING TO A CLOSE AUGUST 25

25 August 2017 -- The Virgo and LIGO Scientific Collaborations have been observing since November 30, 2016 in the second Advanced Detector Observing Run ‘O2’ , searching for gravitational-wave signals, first with the two LIGO detectors, then with both LIGO and Virgo instruments operating together since August 1, 2017. Some promising gravitational-wave candidates have been identified in data from both LIGO and Virgo during our preliminary analysis, and we have shared what we currently know with astronomical observing partners. We are working hard to assure that the candidates are valid gravitational-wave events, and it will require time to establish the level of confidence needed to bring any results to the scientific community and the greater public. We will let you know as soon we have information ready to share.

publiusr
2017-Aug-26, 04:57 PM
Some talk about practical uses of High-Frequency Gravitational Waves:
http://drrobertbaker.com/docs/War%20on%20Terror%20Applications.pdf

01101001
2017-Sep-27, 01:07 AM
First hint of an announcement of August event:

Hanford, Washington, Tri-City Herald: Stay tuned. LIGO observatories to announce latest finding Sept. 27 (http://amp.tri-cityherald.com/news/local/article175492176.html)


An announcement of a new finding from a scientific collaboration that includes LIGO at Hanford is expected Wednesday morning.

The announcement, being made in Turin, Italy, will address an observation made on Aug. 14.

Maybe.

Edit to add second source:

CONFIRMED: A Huge Gravitational Wave Announcement Is About to Happen (https://www.sciencealert.com/new-ligo-gravitational-wave-announcement-august-2017)


It's happening! We have confirmation that the LIGO team will go ahead with the rumoured announcement today at 6:30pm Italian time (that's 12:30pm EST).

slang
2017-Sep-27, 09:25 AM
The article links to a paper on neutron star mergers, which is behind a paywall. This seems to be the preprint from 2015 https://arxiv.org/abs/1512.05435

George
2017-Sep-27, 12:31 PM
Announcement scheduled for 1:30 EDT.

here (https://www.sciencealert.com/new-ligo-gravitational-wave-announcement-august-2017)

01101001
2017-Sep-27, 01:14 PM
Finally it's on a LIGO/VIRGO site, VIRGO website:

Virgo Website: G7 Science - LIGO-VIRGO Collaboration announcement (http://www.virgo-gw.eu/)


At 18:30 (CEST) on Wednesday the 27th of September, the LIGO-VIRGO Collaboration will make an announcement on the science of gravitational waves.

Follow the webcast directly here.

Edit:

Tweet @ego-virgo


EGO-Virgo‏ @ego_virgo 57m57 minutes ago
G7 Science, the press conference will be transmitted at 18.30 in webcast at:
http://www.miur.gov.it/
http://www.virgo-gw.eu

I compute 18:30 CEST, 16:30 GMT, 12:30 EDT, 9:30 PDT

slang
2017-Sep-27, 04:50 PM
Here I sit, paying close attention to socks... watching dead streams :/ ... oh, there it is, finally:

Apparently it's another BHBH merger, but with VIRGO adding to the localisation. Socks still firmly attached.

01101001
2017-Sep-27, 04:51 PM
There was an announcement from VIRGO, but it was not neutron stars merging, just some plain old, black holes. See topic Fourth observation of gravitational waves: two more black holes (https://forum.cosmoquest.org/showthread.php?166673-Fourth-observation-of-gravitational-waves-two-more-black-holes)

If there was a neutron-star merger, it is still in the pipeline.

But the timing, of August 14, might mean it could be the event that had grabbed a lot of observational resources, that raised suspicions.

Maybe there was only one mid-August event. Maybe more. We shall see.

antoniseb
2017-Sep-27, 05:02 PM
I was interested in the graph on the paper showing the relative sensitivity of the three detectors. I hadn't realized that the Louisiana detector was so much better than the other two (at the moment).
I'll be interested in following up on the two-tensor polarization to see what that's about. I expect later runs with higher sensitivity will tell us more about this strong gravity stuff.

It's also curious to me that the BH masses were roughly the same as the ones from the first detection... which seemed high at the time.

Grey
2017-Sep-27, 05:03 PM
Apparently it's another BHBH merger, but with VIRGO adding to the localisation. Socks still firmly attached.We live in a crazy world, where confirmation of a black hole merger (with a final size of over 50 solar masses, and 3 solar masses converted into gravitational wave energy) is just another day of observations. ;)

01101001
2017-Sep-27, 06:21 PM
Something to ponder, from VIRGO site (http://www.virgo-gw.eu):


[...]
Therefore, GW170814 holds great promise for the future of multimessenger astronomy. Additional results, based on data from the three-detector network, will be announced in the near future by the LIGO-Virgo Collaboration; the analysis of the data is currently being finalized.

You suppose "additional results" is more events or more details of this event? I'd like more events, please. The end-of-run announcement spoke of candidates, plural, so I hope there are at least two events observed and soon described.

Virgo only joined up the beginning of August, so if there were two (or more) events in the short run, they were happening frequently.

slang
2017-Sep-27, 07:37 PM
We live in a crazy world, where confirmation of a black hole merger (with a final size of over 50 solar masses, and 3 solar masses converted into gravitational wave energy) is just another day of observations. ;)

Well I suppose the great news is that another observatory has successfully been added to the arsenal. Good news, but not sox blown off.


Virgo only joined up the beginning of August, so if there were two (or more) events in the short run, they were happening frequently.

That paper I linked too spoke of potential detection rates of neutron star + black hole or neutron star mergers in the order of several per year, although acknowledging orders of magnitude uncertainties. So who knows what's still in the pipeline. I might even order some extra socks, just to be safe.

WaxRubiks
2017-Sep-27, 10:51 PM
could gravitational waves come from beyond the observable universe?

Don Alexander
2017-Sep-28, 12:17 AM
Now, that would make them, like, not observable, eh?:rimshot:

Anyway, I've been off the forum way too long... I completely missed this announcement, until a colleague sent me the public link to the LVC paper. :doh:

I have had no chance to read it yet, so I'm not sure how it measures up to 150914. Does not seem to be much fainter in terms of signal strength, and the BHs are pretty massive as well.

antoniseb
2017-Sep-28, 05:33 PM
could gravitational waves come from beyond the observable universe?
What do you mean?
Our best models for them are defined by General Relativity, and they travel at c. Assuming this is correct, the answer is no, they couldn't come from beyond the observable universe. ... but maybe you meant from the other side of the microwave background. The answer to that is maybe, but they are likely very long wave waves.

Don Alexander
2017-Sep-28, 07:43 PM
As an aside, I've wondered if anyone has ever tried to even roughly determine the rate of supermassive black hole mergers in the universe. I actually looked for this via ADS but got no satifactory results. My veeeery rough guesstimate would be 1 in centuries in the entire universe. Quite obviously, something like that would be visible throughout the entire observable universe as well.

antoniseb
2017-Sep-28, 08:05 PM
... My veeeery rough guesstimate would be 1 in centuries in the entire universe. ...
My guess would be much higher, but assumes that in the first few billion years there were a lot of these mergers, and it has slowed down. This assumes there was an age of mergers forming the large galaxies. If this guess is correct there should be several per day.
When LISA is up and running we should get some concrete answers.

01101001
2017-Sep-28, 09:13 PM
Frequencies of plain compact-binary mergers is estimated here: Predictions for the Rates of Compact Binary Coalescences Observable by Ground-based Gravitational-wave Detectors (https://arxiv.org/abs/1003.2480)


Using the detector sensitivities derived from these data, we find a likely detection rate of 0.02 per year for Initial LIGO-Virgo interferometers, with a plausible range between 0.0002 and 0.2 per year. The likely binary neutron-star detection rate for the Advanced LIGO-Virgo network increases to 40 events per year, with a range between 0.4 and 400 per year.

Maybe 40/year detected. About 3/month.

01101001
2017-Sep-28, 11:25 PM
I looked a tiny bit more, using the language from the paper above (Google: smbh coalescence rate) and found several to read. Realistic event rates for detection of supermassive black hole coalescence by LISA (https://arxiv.org/abs/astro-ph/0503210) (URL unwieldy) gave:


Assuming efficient binary coalescence, and guided by the lowest nuclear black hole mass inferred in local galactic bulges and nearby low-luminosity active galactic nuclei (≈10^5 M⊙), we predict approximately 15 detections per year at a signal-to-noise ratio greater than 5, in each of the inspiral and ringdown phases.

There were several others that looked likely, if you want to download them.

Don Alexander
2017-Sep-29, 06:11 PM
Whoa, that many????

Ok, I guess I was overly pessimistic.

I assume these are outside LIGO's observable frequency range, which is why we need eLISA?

01101001
2017-Oct-02, 01:22 PM
Getting back to that tantalizing rumor of the detection of a neutron-star merger on August 17, in a story about the Virgo/Ligo detection of the 4th black-hole merger, Gravitational wave from black hole collision 1.8 billion light-years away sensed in U.S. and Italy (https://www.washingtonpost.com/news/speaking-of-science/wp/2017/09/27/black-hole-collision-1-8-billion-light-years-away-sensed-in-u-s-and-italy/):


[Gabriela González, a professor of physics and astronomy at Louisiana State University] said that the LIGO team is still seeking to confirm several potential detections from the latest observing run, which started in January and ended Aug. 25. She would not say whether the Aug. 17 signal was among them. But González explained that gravitational wave events with optical counterparts can take longer to confirm because of the consistency tests involved.

So, we may have to see some more "ordinary" observations announced before the putative neutron-star merge. That's OK. We like them too.

Don Alexander
2017-Oct-03, 06:09 PM
1. Detect another big BH merger
2. Get Nobel prize
3. ????
4. Profit!

Grey
2017-Oct-03, 06:34 PM
1. Detect another big BH merger
2. Get Nobel prize
3. ????
4. Profit!Given that the Nobel Prize includes a pretty substantial monetary award, I'm not sure that the third unknown step is really necessary in this particular case. ;)

Don Alexander
2017-Oct-04, 06:20 PM
You just wait. :P

01101001
2017-Oct-07, 02:38 PM
Space.com: Gravitational-Wave Announcement Coming on Oct. 16: What Could It Be? (https://www.space.com/38367-gravitational-wave-announcement-coming.html)


It seems very possible that the announcement will be one of four things:


LIGO has detected another pair of merging black holes (the least likely possibility, based on Weiss' comments).
It has detected gravitational waves coming from something other than black holes (most likely neutron stars).
Scientists have pinpointed the source of one of those previously detected black-hole collisions by identifying an associated light signal.
LIGO has found two merging neutron stars and also identified their source location.

chornedsnorkack
2017-Oct-07, 05:25 PM
Given that the Nobel Prize includes a pretty substantial monetary award, I'm not sure that the third unknown step is really necessary in this particular case. ;)

What a Nobel prize does not have is any form of attachment. No way to wear it.

StupendousMan
2017-Oct-07, 11:50 PM
I'll place a wager that the big news is merging neutron stars in NGC 4993, with initial discovery by LIGO and then a counterpart identified in the electromagnetic spectrum.

01101001
2017-Oct-09, 02:20 PM
I assume these are outside LIGO's observable frequency range, which is why we need eLISA?

SMBH mergers: way higher frequency.

This is a helpful diagram I just rediscovered for the speed of gravitational waves (https://forum.cosmoquest.org/showthread.php?166739-speed-of-gravitational-waves) thread: Caltech: Gravitational Wave Spectrum (http://www.tapir.caltech.edu/~teviet/Waves/gwave_spectrum.html). It shows the difference between LISA sensitivity and LIGO, and likely event types. Text there estimates SMBH binaries at 1/year, optimistically.

Don Alexander
2017-Oct-10, 12:58 AM
You mean lower frequency: milliHertz.

01101001
2017-Oct-12, 03:42 AM
Monday, 2017 October 16, 2:00 pm UTC, 10:00 am EDT, 7:00 am PDT.

Science Alert: There's Another Big Gravitational Wave Announcement on The Way (https://www.sciencealert.com/there-s-another-big-gravitational-wave-announcement-on-the-way)


Representatives from 70 other observatories around the world will be at the event, and simultaneous briefings will also be taking place in London and Munich.

There will be two separate panel discussions at the main event, too. The first panel consists of directors and spokespersons from LIGO, Virgo and NASA.

The second panel includes people like David Sand, Nial Tanvir, Eleonora Troja and Andy Howell, who have all performed research into supernovas, and Marcelle Soares-Santos, who is pioneering the Dark Energy Survey's search for an optical counterpart to gravitational wave events.

01101001
2017-Oct-12, 03:45 AM
You mean lower frequency: milliHertz.

Yep. I was reading wavelength and writing frequency. Sorry.

Don Alexander
2017-Oct-13, 08:14 PM
I knew Nial was going to be there, but Nora too! :eek:

Haha, this is so cool! I know these people personally. :)

Looking forward to the press conference!

01101001
2017-Oct-16, 02:55 PM
Rumor rumble over, until the next. It was a neutron-star merger, August 17, detected by 70 observatories, on all continents, throughout the electromagnetic spectrum. Within seconds.

See topic LIGO/VIRGO: Neutron star coalescence (https://forum.cosmoquest.org/showthread.php?166829-LIGO-VIRGO-Neutron-star-coalescence)

Don Alexander
2017-Oct-16, 05:18 PM
Wait, WTF, there is one single post one this??????????????

I thought there would be pages of discussion already... :(

Anyway, now I have at least 37 papers to read. :|

Swift
2017-Oct-16, 06:57 PM
Wait, WTF, there is one single post one this??????????????

I thought there would be pages of discussion already... :(

Anyway, now I have at least 37 papers to read. :|
No, 01101001 linked to entire thread on it.

Selfsim
2017-Oct-16, 09:43 PM
This is absolutely fantastic news and exceeds all expectations as far as I'm concerned!

Congratulations LIGO/VIRGO for a job better than well done! :)

As an aside, I've been waging a battle (elsewhere) with an EU advocate for almost two years now about LIGO's detection capabilities and this just put a nail well-and-truly into his coffin. The individual is very anti-science vocal across the web, (he's an inagural Phil 'bannee') and is responsible for leading many, many science-curious folk astray.

Well done LIGO .. very impressive!

slang
2017-Oct-16, 09:51 PM
I'll place a wager that the big news is merging neutron stars in NGC 4993, with initial discovery by LIGO and then a counterpart identified in the electromagnetic spectrum.

Cheers. :)

slang
2017-Oct-18, 09:21 PM
No, 01101001 linked to entire thread on it.

And that thread is LIGO/VIRGO: Neutron star coalescence (https://forum.cosmoquest.org/showthread.php?166829-LIGO-VIRGO-Neutron-star-coalescence)

Here's the press conference (https://www.youtube.com/watch?v=mtLPKYl4AHs) on Youtube, with two panels and Q&A, cleaned up a bit.

selvaarchi
2017-Oct-26, 01:13 PM
In 2020 we will have another location listening out for gravity waves.

http://www.ecns.cn/m/cns-wire/2017/10-23/278071.shtml

"A world-class observatory under construction at an altitude above 5,250 meters in Ngari Prefecture, Southwest China's Tibet Autonomous Region, will begin efforts to detect primary gravitational waves in 2020.

Ngari is considered an ideal place for astronomers to gaze into the remote universe due to its thin air and clear skies. Chinese scientists will also undertake high-precision detection of cosmic rays in the program called the Ngari Plan."

Sent from my SM-G900F using Tapatalk

antoniseb
2017-Oct-26, 05:38 PM
In 2020 we will have another location listening out for gravity waves....
I understand that India is also building one.
I hope that the new ones can have the same or better performance than the ALIGO in Louisiana. Getting clearer looks at the wave forms will tell us a lot.

StupendousMan
2017-Oct-26, 06:31 PM
I will bet 5 Internet Points that the new Chinese project in the Ngari area is an optical telescope designed to perform followup observations of gravitational wave sources detected by LIGO and VIRGO, rather than an actual detector of gravitational waves itself. The location makes sense for an optical telescope, and the cost and timescale also seem better suited to an optical telescope than something like LIGO.

My guess is that a combination of translation issues and press release jargon has led to a mis-understanding.

Don Alexander
2017-Nov-02, 02:56 PM
I will bet you ten (!) Internet points that it is a submm telescope along the lines of BICEP2 and POLARBEAR, looking at the CMB for the elusive B-mode pola signal.

Notice they say "primary gravitational waves". They likely mean primordial.

Laser interferometers don't need to be put at 5 km altitude, and while that's nice for optical telescopes, it's not a must either. But submm needs extremely low prcipitable water vapor.

Also, this:

https://www.youtube.com/watch?v=LscrBf1CgnE

slang
2017-Nov-16, 10:36 PM
And another one, GW170608 (http://public.virgo-gw.eu/gw170608-ligo-and-virgo-announce-the-detection-of-a-black-hole-binary-merger-from-june-8-2017/), the lightest BH-BH merger detected so far.


This event, detected by the two NSF-supported LIGO detectors at 02:01:16 UTC on June 8, 2017 (or 10:01:16 pm on June 7th in US Eastern Daylight time), was actually the second binary black hole merger observed during LIGO’s second observation run since being upgraded in a program called Advanced LIGO, but its announcement was delayed due to the time required to understand two other discoveries: a LIGO-Virgo three-detector observation of gravitational waves from another binary black hole merger (GW170814) on August 14, and the first-ever detection of a binary neutron star merger (GW170817) in light and gravitational waves on August 17.

Virgo was still in commissioning phase, and the paper (https://arxiv.org/abs/1711.05578) says :

The Advanced Virgo detector was, at the time of the
event, in observation mode with a horizon distance for
signals comparable to GW170608 of 60−70 Mpc. This
was however during an early commissioning phase with
still limited sensitivity, therefore Virgo data are not included
in the analyses presented here.
To me that at least suggests that it did detect it, and would therefor theoretically be the first three detector event, two months before GW170814 (https://en.wikipedia.org/wiki/GW170814).

selvaarchi
2017-Dec-21, 04:00 PM
I understand that India is also building one.
I hope that the new ones can have the same or better performance than the ALIGO in Louisiana. Getting clearer looks at the wave forms will tell us a lot.

Yes they are.

http://www.thehindu.com/sci-tech/technology/a-new-ligo-gravitational-wave-detector-to-be-built-in-india-by-2025/article22149855.ece?homepage=true


A new gravitational wave detector to measure ripples in the fabric of space and time is set to be built in India by 2025, in collaboration with universities from across the globe.

The new Laser Interferometer Gravitational-Wave Observatory (LIGO) detector will add to the two already operational in the US. The LIGO detectors discovered the first gravitational waves produced by two giant merging blackholes last year. The research won a Nobel Prize in Physics this year.

The location for the new detector in India has been selected, and the acquisition has started, said Somak Raychaudhury, Director of the Inter-University Centre for Astronomy and Astrophysics (IUCAA) Pune. However, the site has not been revealed yet.

selvaarchi
2018-Apr-05, 08:23 AM
China has other plans as well.

http://www.ecns.cn/2018/04-03/297947.shtml


Progress on the Tianqin project, a Chinese research project to detect gravitational waves, was revealed to the public on Monday.

The Guangzhou-based Sun Yat-sen University started the Tianqin project in July 2015 and is being led by Luo Jun, a university physicist, who told China Central Television (CCTV) that the project was named after a metaphor.

"If you send three satellites in orbit at a distance of about 100,000 kilometers and connect the three by laser beams, the space formation looks like a harp and when the gravitational waves come, there will be disturbances. The wave was like the hand of God which plucks the string," Luo said.

Research began in a bomb shelter under the Yujia mountain in Central China's Hubei Province. And the research on gravitation commenced in 1983 when Luo first joined the lab in the shelter, the CCTV report said.

A two minute video, in Mandarin though, on a space based system

http://www.cctvplus.com/news/20180401/8077318.shtml#!language=1


Tianqin, China's gravitational wave research project, plans to launch three satellites around 2030 to measure the change of time and space, said Luo Jun, initiator of the project and an academician of the Chinese Academy of Sciences (CAS) on Wednesday during an interview with China Central Television.

Gravitational waves are "ripples" in the fabric of time and space caused by movements of celestial bodies in the universe. Albert Einstein predicted its existence in 1916 in his theory of relativity. And in 2016, scientists with the American Laser Interferometer Gravitational-wave Observatory (LIGO) discovered gravitational waves.

According to experts, Tianqin, different from the research by the U.S. ground-based observatory, will observe the waves from space. It is likely to collect better information, as a larger black hole may be detected from space than the one detected from the ground.

Luo Jun said he and his team will carry out a four-stage plan over the next 15 to 20 years to detect the waves with three high-orbit satellites.

selvaarchi
2019-Oct-06, 01:36 PM
Japan will have their detector working by December.

https://www.geekwire.com/2019/japans-kagra-detector-joins-ligo-virgo-international-hunt-gravitational-waves/


apan’s Kamioka Gravitational-Wave Detector, or KAGRA, is due to start teaming up with similar detectors in Washington state, Louisiana and Italy in December, boosting scientists’ ability to triangulate on the origins of cataclysmic cosmic events such as black hole smash-ups.

Representatives of KAGRA, the U.S.-based Laser Interferometer Gravitational-Wave Observatory (LIGO) and Europe’s Virgo detector signed a memorandum of agreement today in Toyama, Japan, to confirm their collaboration. The agreement includes plans for joint observations and data sharing.

“This is a great example of international scientific cooperation,” Caltech’s David Reitze, executive director of the LIGO Laboratory, said in a news release. “Having KAGRA join our network of gravitational-wave observatories will significantly enhance the science in the coming decade.”

Nobel-winning physicist Takaaki Kajita, principal investigator of the KAGRA project, said “we are looking forward to joining the network of gravitational-wave observations later this year.”