## Saturday, March 03, 2012

### Hubble: decoupling of dark matter, stars

Alan Boyle of Cosmic Log discusses an amusing picture of the merging galaxy cluster Abell 520 which is 2.4 billion light years from us, as seen by the Hubble Space Telescope. The positions of the colors are mystifying.

The blue color on the picture depicts the mass density (as obtained from an analysis of gravitational lensing) – it's dominated (and therefore almost identical to) the distribution of the dark matter. The green color depicts hot gas. And the orange color shows starlight emitted by the galaxies.

The locations don't coincide at all! The dark matter seems to have coalesced in the middle while the stars and hot gas remain at the peripheries.

You know some of the famous pictures in which the distribution of dark matter and stars was shifted relatively to each other. Those pictures of the Bullet Cluster, a scenery that is 3 billion light years from us, have been used as an argument in favor of the existence of dark matter. However, the picture above shows too much of the same good thing!

It's a nearly complete divorce of the dark matter and the visible one.

A confusing report on the observation, published in The Astrophysical Journal, is also available as an arXiv preprint:
A Study of the Dark Core in A520 with Hubble Space Telescope: The Mystery Deepens
The authors, M. J. Jee, A. Mahdavi, H. Hoekstra, A. Babul, J. J. Dalcanton, P. Carroll, P. Capak, offer several explanations, none of which is clearly better than the other explanations.

Off-topic: Pilsner music

The Mandrage band has existed since 2001 and it was largely unknown. However, it just happened that at the end of 2011, its fame exploded. As of early 2012, it has several songs at the top of the Czech hitparades. The song below has spent 10 weeks at the very top of the national radio hitparade.

I embedded the video "Screws, Nuts, and Matrix String Theory" now when I learned that the guys are actually citymates from Pilsen. See also Francis Spa Town (Františkovy Lázně).