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  1. #61
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    Quote Originally Posted by SRH View Post
    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.
    Forming opinions as we speak

  2. #62
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    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?

  3. #63
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    Quote Originally Posted by Cougar View Post
    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.

  4. #64
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    Quote Originally Posted by SRH View Post
    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. Jumps emitting EM radiation would become more frequent as the annihilation approaches, kind of sort of like a gravitational merger "chirp".

  5. #65
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    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.

  6. #66
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    Quote Originally Posted by SRH View Post
    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.

  7. 2016-Feb-13, 05:38 AM

  8. #67
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    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?

  9. #68
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    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.

  10. #69
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    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.

  11. #70
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    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.

    Quote Originally Posted by Sticks View Post
    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.

    Quote Originally Posted by Sticks View Post
    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?

    Quote Originally Posted by Sticks View Post
    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?

    Quote Originally Posted by Sticks View Post
    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.
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  12. #71
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    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/NewsCon...spx?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.

  13. #72
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    Quote Originally Posted by slang View Post
    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.

  14. #73
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    Quote Originally Posted by Sticks View Post
    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.

  15. #74
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    Quote Originally Posted by eburacum45 View Post
    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.

  16. #75
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    Since/if GW travel at speed of light, has there been simultaneous collaborative visual/electromagnetic observations? If so has there been any lagging observed?

  17. #76
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    Quote Originally Posted by StupendousMan View Post
    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.

  18. #77
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    Quote Originally Posted by a1call View Post
    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).

  19. #78
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    Quote Originally Posted by a1call View Post
    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.
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  20. #79
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    Quote Originally Posted by Don Alexander View Post
    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).
    Forming opinions as we speak

  21. #80
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    Quote Originally Posted by Don Alexander View Post
    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.
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  22. #81
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    Quote Originally Posted by Don Alexander View Post
    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.

  23. #82
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    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/Hydr..._uses_for_SETI

  24. #83
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    I was thinking it could be an alien warp drive.

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    Quote Originally Posted by eburacum45 View Post
    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.
    Conserve energy. Commute with the Hamiltonian.

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    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.

  27. #86
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    Quote Originally Posted by a1call View Post
    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.
    Forming opinions as we speak

  28. #87
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    Quote Originally Posted by antoniseb View Post
    ...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.

  29. #88
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    Quote Originally Posted by a1call View Post
    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.
    Quote Originally Posted by Grey View Post
    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.

  30. #89
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    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

    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.
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    So that's what those funny sensations have been.

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