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posted by CoolHand on Wednesday April 15 2015, @06:22PM   Printer-friendly
from the dark-matter-matters dept.

Two recent studies are attempting to shine light on dark matter.

The Dark Energy Survey (DES) has published its preliminary findings. The project is attempting to map dark matter across 1/8 of the sky using 570-megapixel imagery from the Victor Blanco telescope at the Cerro Tololo Inter-American Observatory, in the Chilean Andes. The early results are a test of the project's first images and cover just 0.4% of the sky, yet it is "the largest contiguous dark matter map" ever made, revealing exactly where dark matter is concentrated amid 2 million galaxies.

A separate finding published this week in the Monthly Notices of the Royal Astronomical Society may reveal how dark matter can interact with itself:

For the first time, the enigmatic quantity may have been caught interacting with other dark matter in a cluster 1.4 billion light-years away.

[...] A team of astronomers led by Dr Richard Massey of Durham University studied a simultaneous collision of four galaxies in the cluster Abell 3827.

Although dark matter cannot be seen, the team was able to deduce its location using a technique called gravitational lensing. While dark matter does not absorb or emit light, it does have gravity.

So it bends the path of light passing nearby, warping our view of anything on the other side of it. The dark matter in Abell 3827 bent the path of light rays coming from a distant background galaxy, which happened to be aligned just right for the team's purpose.

The researchers found that one dark matter clump appeared to be lagging behind the galaxy it surrounds. Such a lag between the dark matter and its associated galaxy would be expected if the mysterious stuff was interacting with itself - through forces other than gravity.

 
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  • (Score: 2) by FatPhil on Thursday April 16 2015, @08:59AM

    by FatPhil (863) <pc-soylentNO@SPAMasdf.fi> on Thursday April 16 2015, @08:59AM (#171484) Homepage
    > > ~r^-1.(1+r)^-2

    > Oops, my mistake. Not uniform then, but centrally distributed and more dense in the middle.

    That's density, yup, but the middle is very small - effectively it's just a blip. Multiply by r^2 to get actual mass at each distance, and you'll see there's more mass at r=1 than anywhere else. (Which is why I mentioned it non-converging - it scales like 1/r in the shell at distance r for r >> 1, which is a divergent integral as r->inf.)

    And no I do not have a better model. For the hypothetical mass distribution, based on galactic rotation speed, that model doesn't look too bad. More measurements from more galaxies of various types should tell us more about its shape. However, the proponents of that, or any other, model don't have a reason why the distribution should have that shape any stronger than that of it making the curves fit. There's no gem of insight in that, no understanding, just plotting.

    I object more to the certainty with which some (N.K-H.) put forward their explanations for what the mass *is* and how it behaves (yes, it sounds like a predictive theory - which is good - but he always goes quiet whenever an experiment proves his theory unlikely, until he's got funding for the next bigger experiment which will prove him right this time).

    But I don't think that modified theories of gravity can be completely dismissed either.
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