Deflating Claims That ESA Craft Has Spotted Dark Matter

Yesterday, we posted news that data from the European Space Agency's XMM-Newton spacecraft had been interpreted as a possible sign of dark matter; researchers noted that a spike in X-ray emissions from two different celestial objects, the Andromeda galaxy and the Perseus galaxy cluster, matched just what they "were expecting with dark matter — that is, concentrated and intense in the center of objects and weaker and diffuse on the edges." StartsWithABang writes with a skeptical rejoinder: There seems to be a formula for this very specific extraordinary claim: point your high-energy telescope at the center of a galaxy or cluster of galaxies, discover an X-ray or gamma ray signal that you can't account for through conventional, known astrophysics, and claim you've detected dark matter! Only, these results never pan out; they've turned out either to be due to conventional sources or simply non-detections every time. There's a claim going around the news based on this paper recently that we've really done it this time, and yet that's not even physically possible, as our astrophysical constraints already rule out a particle with this property as being the dark matter!

Comments

Re:Dark matter and the sniff test

[Anonymous Coward]

There's a few scenarios were evidence of dark matter has been observed. All you have to do is smash two galaxies together and the non-interacting dark matter separates from ordinary matter. The separated dark matter then causes a gravitational lensing effect, which is displaced from the ordinary/visible matter in the galaxies.

It's possible that a modified theory of gravity (e.g. MOND) could still account for the behavior, but it puts requirements on the theory that (I am told) are difficult to accomodate. Sort of like how the Higgs boson discovery at 125 GeV puts requirements on supersymmetry that are hard to accomodate--it's still possible, but much less appealing.

This particular theory (variability of C) is one that crops up periodically, most recently in 2013 [livescience.com]. It is difficult to prove, but really, it's no more unlikely than the existence of huge amounts of dark matter that stubbornly refuse to interact with the known universe.

Considering it's 100% likely that there are particles which don't interact electromagnetically or via the strong force (i.e. neutrinos), dark matter isn't a stretch at all. It's strictly required to exist in most beyond standard model theories. And since the standard model sucks at explaining some observations (e.g. the maginitude of CP violation), we have reason to believe there's more physics going on than what we can currently observe.

Re:Dark matter and the sniff test

[Dutch Gun]

Indeed there is probably something going on at large scales, where gravity doesn't work as it does on small scales.

I've often wondered about that. It's pretty well known that classical Newtonian physics tends to break down at the quantum level. I wonder if the same thing happens at the largest scales - galaxy-sized measurements. I'd never go so far as to argue against the prevailing theory with people that study these things their entire lives, but it does make for interesting reading and/or discussion to consider some of the proposed alternatives.