Mysterious X-ray Signal Hints At Dark Matter 100
Astronomers using the Chandra X-ray Observatory and the XMM-Newton have recorded an unusual emission of X-ray light from a remote cluster of galaxies which may turn out to be evidence of dark matter.
Astronomers think dark matter constitutes 85% of the matter in the Universe, but does not emit or absorb light like “normal” matter such as protons, neutrons and electrons that make up the familiar elements observed in planets, stars, and galaxies. Because of this, scientists must use indirect methods to search for clues about dark matter. he latest results from Chandra and XMM-Newton consist of an unidentified X-ray emission line, that is, a spike of intensity at a very specific wavelength of X-ray light. Astronomers detected this emission line in the Perseus galaxy cluster using both Chandra and XMM-Newton. They also found the line in a combined study of 73 other galaxy clusters with XMM-Newton. ... The authors suggest this emission line could be a signature from the decay of a "sterile neutrino." (Abstract.) Sterile neutrinos are a hypothetical type of neutrino that is predicted to interact with normal matter only via gravity. Some scientists have proposed that sterile neutrinos may at least partially explain dark matter.
Re:Why isn't time dark matter? (Score:5, Informative)
Basically, IIRC, the best models that we have to explain the Universe say the Universe should have X amount of matter in it. When we look at the Universe, though, we see only 15% of X existing. So either our models are wildly off or there is a type of matter out there that we can't currently detect (so-called "dark matter" because we can't see it). In the case of the former, it's possible, but that would toss other theories - with more firm proof for them - out as well. In the case of the latter, it's completely possible that there is sort of a self-selection bias in play. We see normal matter regularly so our detection methods have been geared towards normal matter and miss the dark stuff.
Re:Doesn't jive for me (Score:4, Informative)
The hypothesis is not that the X-Rays are interacting with this type of dark matter. It is that the decay of this type of dark matter generates X-Rays.
Re:This too shall pass (Score:3, Informative)
Also the idea that space it self isn't flat has also been investigated (Not an astrophysicist, but if I remember correctly current verdict is it's flat/nearly flat).
The whole point of General Relativity, about to turn 100 years old next year, is that space is not flat on various scales. Observation suggests on the largest scales it averages out to flat, but physicists have put a lot of effort into understanding non-flat space on smaller scales (and even large scales in case observations are wrong).
Re:Doesn't jive for me (Score:5, Informative)
It's the ambiguity of language that's at fault here. The key to the sentence you mentioned is "like normal matter". Normal matter absorbs electromagnetic radiation, increasing its energy level, and drops back to lower energy levels by emitting electromagnetic radiation. Thus, normal matter interacts with light. This is a different physical process than the emission of light due to decay of the particle itself.
And while we haven't pinned down dark matter by any means, it's much more than a stab in the dark. For one, there are known particles--neutrinos--that do not interact via the electromagnetic force, so the idea of unknown particles with the same property isn't unrealistic.
Then, there are clues from many different directions that point to something consistent with matter that interacts gravitationally but not electromagnetically. These include calculations concerning the total matter in the universe, galaxy cluster formation, the rotational speed of stars on the out edge of galaxies, etc.