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View Full Version : A History of the Universe Written in Gamma Rays



Fraser
2006-Apr-24, 03:37 PM
SUMMARY: When astronomers look into the sky, they see bright objects, but also a diffuse glow coming from objects across the Universe in many different wavelengths. This glow could serve like a fossil record, to help astronomers untangle the different stages the Universe went through from the beginning, to the current day. Research teams are using very high energy gamma rays, generated in the most violent objects in the Universe - quasars - as a probe to understand this background light.

View full article (http://www.universetoday.com/am/publish/vhe_gamma_rays.html)
What do you think about this story? post your comments below.

Joff
2006-Apr-24, 04:49 PM
I wasn't aware that photons interected with each other at all (once I realised that interference etc. was each photon interecting with itself). Is this a low-probability interaction? Can I shine two laser beams at each other in a vacuum and have some kind of scatter to the side?

antoniseb
2006-Apr-24, 05:57 PM
This was an interesting story. There may be a number of similar stories we will get as we improve the resolution with which we observe distant objects at different wavelengths. TeV gamma rays are blurred by microwave photons. Optical wavelengths my be blurred or lensed very slightly by intergalactic gasses or other factors. We are getting near some interesting and tattle-tale limits that will narrow our choices of theories of the universe.

trinitree88
2006-Apr-24, 06:23 PM
I wasn't aware that photons interected with each other at all (once I realised that interference etc. was each photon interecting with itself). Is this a low-probability interaction? Can I shine two laser beams at each other in a vacuum and have some kind of scatter to the side?

Joff. I too thought that Einstein-Bose statistics allowed bosons to pile up without limit in a confined region of space, and intersecting laser beams to pass through each other unimpeded...are we now saying this is untrue? The only rationale I'd have is that your "shine two laser beams at each other in a vacuum"...is not technically an empty region of space....there is as yet no way to remove the neutrino sea background from it.....and neutrinos may act on photons via the neutral current...the Z0...it's universal, and acts on all the particles in the Standard Model. :think: Pete.

Joff
2006-Apr-24, 06:45 PM
Joff. I too thought that Einstein-Bose statistics allowed bosons to pile up without limit in a confined region of space, and intersecting laser beams to pass through each other unimpeded...are we now saying this is untrue? The only rationale I'd have is that your "shine two laser beams at each other in a vacuum"...is not technically an empty region of space....there is as yet no way to remove the neutrino sea background from it.....and neutrinos may act on photons via the neutral current...the Z0...it's universal, and acts on all the particles in the Standard Model. :think: Pete.
Curse those neutrinos! They're everywhere! :lol:

I'm not sure how neutrino interactions would take us closer to examining the background light that the gammas travelled through, however, unless those neutrinos that have had some kind of interaction with the background light are then in a state which changes their interaction with a gamma.

antoniseb
2006-Apr-24, 07:13 PM
Curse those neutrinos! They're everywhere!

I'm going to have to make a T-shirt that says that!

trinitree88
2006-Apr-24, 07:40 PM
:D
I'm going to have to make a T-shirt that says that!

lol.:lol: :clap: :shifty: :whistle: Pete

Joff
2006-Apr-24, 08:14 PM
Well, I'm not greedy - 10c per T-shirt for use of the phrase.

Gerald Lukaniuk
2006-Apr-24, 08:44 PM
I'm going to have to make a T-shirt that says that!

I've had some made out of neutrinos. They very expensive but only real physicists and good astronomers can actually see them or put them on. Any buyers?

antoniseb
2006-Apr-24, 08:44 PM
I plan to make one. where do you want the 10c?

Joff
2006-Apr-24, 09:39 PM
To you, it's free for posting a picture of it on the web (let me know where).

antoniseb
2006-Apr-24, 09:45 PM
Thanks. It may take a while, but it'll happen.

TimLong
2006-Apr-25, 03:16 PM
Just like in a laser fusion target chamber, beams targeted into a spheric symmetric orientation (in phase) will give output energies which go as the square of the number of beams. This also shows that photons can interfere - and in random interactions in space, pair formation could even occur. There are cosmological theories that describe this as the mechanism for the creation of matter out of the vacuum.

Joff
2006-Apr-25, 06:30 PM
Just like in a laser fusion target chamber, beams targeted into a spheric symmetric orientation (in phase) will give output energies which go as the square of the number of beams. This also shows that photons can interfere - and in random interactions in space, pair formation could even occur. There are cosmological theories that describe this as the mechanism for the creation of matter out of the vacuum.

That's weird and I must admit it sounds too good to be true - fire 20 beams in and get 400 times the energy of one beam... do you have anything else I could read on this?

Jerry
2006-Apr-25, 07:31 PM
So...The Big Bang afterglow is a lot less than expected, meanwhile the X-ray point source count is much greater than expected.

Another Big Bang prediction in the dumpster. It is getting rather crowded in there.

RussT
2006-Apr-26, 12:11 AM
Yes, and this is yet another piece of evidence that fits perfectly with my concept.

five_distinct
2006-Apr-26, 05:36 PM
What's your concept, RussT?

Tensor
2006-Apr-26, 06:49 PM
So...The Big Bang afterglow is a lot less than expected, meanwhile the X-ray point source count is much greater than expected.

Ahhhh, Jerry, are you refering to the article? The BB afterglow and extragalactic background light(EBL) are two different things. The BB afterglow comes strickly from the last scattering. The EBL comes from photons emitted from all light emitting massive objects (stars, galaxies, quasars, etc). The frequencies are different. Not to mention, the article didn't even mention X-ray point sources, it talks about gamma ray sources.


Another Big Bang prediction in the dumpster. It is getting rather crowded in there.

Well, another of your misunderstandings resulting in you thinking another prediction is wrong. Is it really any wonder some of us have a hard time taking your ideas seriously, when you can't even get the ideas in a press release straight?

RussT
2006-Apr-27, 07:29 AM
[maximum amount of this 'extragalactic background light', which is remarkably lower than what previous estimates had suggested.]

However, Tensor, this is very significant, because it means that that farther you go back, the less galaxies and starlight you will see.

Tensor
2006-Apr-27, 12:38 PM
[maximum amount of this 'extragalactic background light', which is remarkably lower than what previous estimates had suggested.]

However, Tensor, this is very significant, because it means that that farther you go back, the less galaxies and starlight you will see.

Not sure where you get this from. The EBL is dependent on two things, the number of sources and the amount of scatter. The number of sources we can see. The amount of scattering is dependent on several factors and the discovery that the amount of scatter is lower suggests that one or more of those factors isn't what we thought it was.

As far as there being less to see:


The discovery of lower levels of intergalactic starlight has the interesting side effect that the Universe becomes more transparent to gamma rays and that the telescopes can look deeper into the cosmos, increasing their reach for further discoveries!"

Which means that we can see more(at least in gamma rays) than previously thought.

RussT
2006-Apr-27, 10:05 PM
First Image - A cartoon of the effects of the diffuse extragalactic background light (EBL) on the gamma-ray emission from a distant quasar, before reaching the Earth. The gamma-rays are partly absorbed by colliding with the EBL photons produced by all the stars and galaxies in the Universe. If the density of EBL photons is high (upper graph), absorption is high and the highest energy gamma-rays are lost. So the distribution of measured energies (spectrum) is strongly changed. If instead the density is low (lower graph), absorption is less and the spectrum is not changed as much.
(credit: HESS Collaboration)


Second Image - The HESS spectrum of the blazar 1ES 1101-232. The HESS spectrum of the blazar 1ES 1101-232. The observed distribution of energies (spectrum) of the detected gamma-rays is plotted in red. In blue is shown the deduced original distribution as emitted at the source, reconstructed supposing different levels of the diffuse background light. If the level is high (left and centre panel), the original spectrum is dramatically different from the typical distribution expected from such objects, and cannot be easily explained as an intrinsic feature. With a low background light level (right panel), the original spectrum becomes compatible with the normal characteristics of this type of quasar.
(credit: HESS Collaboration)
For further information visit the Max Planck Institute website.

Tensor, if you go to the bottom of the first article and click on the full article, you will see these.

Both of these just talk about the EBL, and not other sources for the scatter, in fact another statement farther down virually eliminates any other scatter components, other than the stars and the galaxies, which is actually the only place stars are, even in the early universe!

This report also has implications for the CMB, since it is supposedly caused by the last scattering of "Gamma" photons, but I can't quite puy my finger on exactly how this could apply, yet.

Tensor
2006-Apr-28, 03:24 AM
Both of these just talk about the EBL, and not other sources for the scatter, in fact another statement farther down virually eliminates any other scatter components, other than the stars and the galaxies, which is actually the only place stars are, even in the early universe!

Russ, I really wish you would look at the actual papers. The stars and galaxies are the sources for the EBL, not the scatter components. Intergalactic and interplanetary dust, among other things, can affect the scatter measurement. For example, there is a reflected sunlight component with interplanetary dust. Intergalactic dust has a thermal emission component ~260K. In addition, extragalactic sourses such as the LMC and SMC add a local foreground component that has to taken into acccount. If a measurement is being taken from an earth-bound device, the reflection, of man made light, from the atmosphere also has to be taken into account.


This report also has implications for the CMB, since it is supposedly caused by the last scattering of "Gamma" photons, but I can't quite puy my finger on exactly how this could apply, yet.

Sigh....while originally gamma photons, the CMB photons have been redshifted into the microwave region (the M in the CMB). For the CMB, which has been shifted through almost the entire spectrum, we need to determine the opacity if the EBL on almost the entire spectrum, as those photons travel to us, not just the gamma wavelengths. Remember, the EBL can have a different opacity depending on the wavelength.

Now, Fraser's link spoke of the EBL and Gamma rays, not the BB afterglow (CMB) and X-ray point sources as Jerry's comment indicated.

RussT
2006-Apr-28, 07:47 AM
Russ, I really wish you would look at the actual papers. The stars and galaxies are the sources for the EBL, not the scatter components. Intergalactic and interplanetary dust, among other things, can affect the scatter measurement. For example, there is a reflected sunlight component with interplanetary dust. Intergalactic dust has a thermal emission component ~260K. In addition, extragalactic sourses such as the LMC and SMC add a local foreground component that has to taken into acccount. If a measurement is being taken from an earth-bound device, the reflection, of man made light, from the atmosphere also has to be taken into account.

Tensor, I do appreciate your responses and knowledge, but I read every word in the link in the OP, and also read everything clicking on the 'original article', and neither of those reports said one word about the scattering you are talking about. And of course I expexted that they took out any local scattering effects anyway.

And now you are (slightly) reprimanding me for not going farther and clicking on the Web Page to find The PDF paper (you are evidently rerfering to), which I can't read anyway, because my PDF is all screwwed up.

I obviously wouldn't mind you pointing out that there is additional information that wasn't included in the original article, but surely it is not incumbent on anyone to click on all links on a particular subject, to be able to make a comment, or give an opinion about a particular finding.

I am still contending that the 'remarkably lower' EBL is very significant.



Sigh....while originally gamma photons, the CMB photons have been redshifted into the microwave region (the M in the CMB).

Didn't need the 'sigh'...of course I know this, but they made a pretty big thing saying these were the most distant QSO's (Blazars), so since they are so distant, they should be redshifted almost to the microwave region also, correct?

So, based on your next statement, I can see that I do not understand 'opacity'.

To me it sounded as though after measuring the gamma rays at their wavelength here at earth, that they reconstructed what the Gamma wave would be at the quasar, and found it to be too blue there.

I also find it interesting, that they are saying that Gamma photons are more transparent than they thought, which again makes me think that could have some affect on the CMB.