CMB troubles.
4 Sep 2006 17:42:19 UTC
Topic 191784
(moderation:
I found an interesting article on the cosmic microwave background. Professor Richard Lieu, of the University of Alabamu in Huntsville, looked at 31 nearby x-ray emitting galaxy clusters in search of shadows.
The theory is that if the microwave background is coming from behind the clusters, as it should be if the Big Bang theory is correct, they should cast shadows, just like objects here on Earth cast shadows on the ground when the sun shines on them.
The problem is, Dr. Lieu only found a quarter of the expected shadows!
http://www.moondaily.com/reports/Big_Bang_Afterglow_Fails_An_Intergalactic_Shadow_Test_999.html
Click my stat image to go to the BOINC Synergy Team site!
CMB troubles.
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An interesting paper.
IIRC, the preprint was first submitted about a year ago, and has been revised several times. I don't know if it's actually been published - certainly the early preprint I read contained some shortcomings.
In any case, the result should be regarded as tentative at best - WMAP is a poor instrument to observe the SZE, even for nearby clusters, and the signal is pretty much at the limit of detectability; much better would be the results of dedicated SZE projects (of which there are several). It will be interesting to see how well they match the Lieu results.
I was under the impression
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I was under the impression that the CMB radiation existed throughout all of space equally so then wouldn't there not be any shadows?
RE: I was under the
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Hopefully this explanation is correct:
The radiation originates (or is leftover) from the 'surface of last scattering', when the universe was still so hot that the whole sky was opaque, not transparent to the radiation, but instead scattering the radiation like fog. So the radiation was scattering everywhere, in all directions, until the universe finally cooled enough to become transparent (about 400,000 years after the big bang), at which point the radiation stopped scattering and began its long journey (from everywhere, heading in all directions) to become what we currently detect as microwaves, coming from all points in the sky.
So what's the distance, in light-years, from here to the nearest galaxies? That's about the amount of time (in years) it would take for leftover radiation from the big bang to arrive here from the nearest galaxies. Even if the distance is millions of light-years, that radiation would have arrived here long ago, since many billions of years have elapsed since the time of the 'surface of last scattering'. So the radiation we're detecting now has traveled that amount of time (many billions of years), and so it must have originated beyond the nearest galaxies, and some of these galaxies should cast a shadow in the CMB...
Regarding the article in the OP, what else could it be other than foreground emission, for the galaxies that aren't casting a shadow? I found a good chart showing which projects and instruments are working on detecting which type of source (from many possibilities in addition to the CMB) it is, for the microwaves that are detected coming from a specific part of the sky. The chart is from Max Tegmark's cosmology library. (I wish I would've found this site about a week sooner, re: my SFHe DM conjecture on one of the other threads. I see now some of the many reasons (as Ben Owen thankfully pointed out there are) why dark matter couldn't be superfluid helium, such as the scientist's ability to discern between such sources as dust emission, synchrotron radiation, free-free-emission, and unresolved point sources, apart from the CMB, with its 'surface of last scattering'(link is to WMAP's cosmology 101), which is important for learning about origins of galaxies and large scale structure of galaxies, and also for measuring the basic parameters of the Big Bang theory.)
There is a conventional
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There is a conventional explanation for the anomalous Sunyaev-Zel'dovich effect
from the same author. See: http://arxiv.org/abs/astro-ph/0607304
Hope this will help
RE: There is a conventional
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Does this mean that observing the SZE will be somewhat less prevalent than originally anticipated? In those clusters where it is observed, how is the AGN activity (and Alfvenic heating) different from the anomalous clusters?