Possible Dark Matter Signs At the Core 234
Scientific American has a piece on speculation that dark matter may be behind diffuse radiation in the galactic center. Beginning in 2003, researchers led by Douglas Finkbeiner noticed a curious excess of microwave radiation in the WMAP data, after all known sources of such radiation were accounted for. Data from NASA's Fermi Gamma-Ray Space Telescope resulted in a similar anomaly in gamma rays. "A paper posted to the physics preprint Web site arXiv.org on October 26 and submitted to the Astrophysical Journal points to a possible signature of dark matter in the Milky Way, although the study's authors are careful to keep their observations empirical and table such speculation... In the new paper [the researchers] describe the Fermi gamma-ray haze and make the claim that it confirms the synchrotron origin of the WMAP microwave haze. And as with the microwave haze, the authors argue that the electrons responsible for the gamma-ray haze appear to originate from an unknown astrophysical process. ... 'We are absolutely in the process of exploring the Fermi haze in the context of dark matter physics,' [one of them] says."
Re:It's a black hole! (Score:5, Informative)
Black hole and dark matter have very precise meanings in physics. In fact, black holes aren't strictly black due to Hawking radiation and dark matter is transparent, not dark.
Re:Explanation Impossible (Score:4, Informative)
Like "gravity", dark matter is the name given to a phenomenon or set of phenomena that appear related, not necessarily an actual thing or force. We don't know what gravity actually "is" under the hood; we only know what it does. Gravity is a model that explains observations nicely. But the actual workings behind it are still elusive. We've yet to successfully break it down into sub-mechanisms or sub-models, like knowing that cars move and the patterns of their movements, but not why they move.
Dark matter may actually be many different forces or causes, and perhaps in the future may be split up or re-assigned to other "forces" (models). At this point in time it's merely a guess that it's all one thing. Gravity may also turn out to be multiple things that only appear to be one in the same from our limited perspective and observations. We have to peel the onion one layer at a time, and may never reach the final center layer (if there is such a thing).
Explanation Very Possible (Score:5, Informative)
Can't explain something, Dark Matter is the reason! Can't find a cause, Dark Matter is it!
This is completely incorrect. This work is the result of looking for Dark Matter. Dark Matter is the best explanation for galactic rotation curves and the cosmic microwave background. Depending on what the Dark Matter is it may annihilate with itself and produce, amongst other things, electron-positron pairs. In fact the paper is really a very beautiful and elegant bit of work since the first bit of evidence which lead to this comes from the background 'noise' of one of the major pieces of evidence for Dark Matter - the WMAP data! As such, far from noticing something and then attributing it to Dark Matter, this is actively looking for something that suggests evidence for Dark Matter. True the evidence does not show that it HAS to be Dark Matter but if you cannot attribute it to anything else which is known and you have models which suggest that Dark Matter might produce such a signal it is very interesting.
Arkani-Hamed et al have a model which may explain this and which, if correct, predicts jets of leptons (electrons or muons) at the LHC. This is actually one of the things which my colleagues and I are looking for on the ATLAS Experiment [atlas.ch]. If we do observe them then this will be further evidence for Dark Matter and not a "oh, something else we cannot explain and put down to Dark Matter". Until we have enough bits of evidence that, combined, show that Dark Matter is the only possible cause there will always be some doubt but that should not be construed as flailing around and using Dark Matter to explain every observation that is inexplicable. Indeed, the fact that we are using Dark Matter models to suggest observations and experiments to perform and then finding that these return "inexplicable" results is very, very interesting!
Re:Explanation Impossible (Score:5, Informative)
Simulations of stars in galaxies are approximations because: />3) newton's equations are indeed incorrect however, Einstein's equations only dominate to a significant degree under unusual conditions.
1) there isn't an equation for an exact solution to any gravitationally bound system containing more than 5 objects.
2) stars in a typical galaxy are not uniform so the simulations must take this into account as a best guess. br
In so far as dark matter is concerned, you are incorrect. Experiments like the Cryogenic Dark Matter Search are attempting to detect dark matter particles directly, we've got neutrino detectors looking for evidence of annihilation events... Particle accelerator experiments attempting to actually synthesize dark matter candidates.. To claim that there isn't a way to test the dark matter hypothesis would be grossly inaccurate.
Disclaimer: Physics isn't my major but I did study quite a bit of it in high school and college.
Re:Call me an astrophysics noob, but (Score:3, Informative)
Because the massive black holes don't adequately explain things.
Rotation speeds of stars about the center of the galaxy don't behave as they should in the case where the massive black hole is the only thing acting on them other than nearby bits of galaxy.
Re:It's a black hole! (Score:3, Informative)
Instead of questioning the standard model (giving us dark matter), we could question general relativity. This gives us a theory called MOND.
Actually, no. It gives you an "I don't know." That's unacceptable, so MOND emerges to fill the gap.
Seriously, you actually believe that? It's useless, not unacceptable. If all scientists did is say "I don't know" they wouldn't get much done would they? Think about it for a minute. Or, they do what scientists do best (i.e. science) and come up with new theories (e.g. MOND) which make testable predictions and attempt to test them.
Re:It's a black hole! (Score:1, Informative)
Nihil verum nisil mors
Re:Explanation Impossible (Score:3, Informative)
This is what computers were designed to do, but instead of just doing a numerical simulation, physicists insist on waving their hand and dismissing the error term like it's not even there, so they can keep using nice pretty exact solutions that... don't agree with reality.
I think these people [dur.ac.uk] may disagree with you.........
You'll find most of those simulations are Newtonian. I just checked some of their latest papers, and they all use Newtonian or modified Newtonian (MOND) codes. The code they run is called "GADGET-3" (they also used earlier versions in the past), and according to this [www.aip.de] high level description, it's Newtonian. Admittedly, it's an impressive simulator, but it seems to concentrate on scale (many particles) and on including many effects like gas interactions, magnetohydrodynamics, etc... but not a relativistic metric.
If you can find even one of the published papers on that site that even mentions to worth 'relativistic', I'd be very interested in reading it. The papers are linked from here [dur.ac.uk], they have links to the full papers on Arxiv.