Chandra :: Photo Album :: 1E 0657-56 :: 21 Aug 06
The issue of the reality of dark matter has kept coming up recently in my life, both in the writing and educational spheres. I recently finished copy edits on the new book (SPIDER STAR will hit stores in March 2008 and I'll blog about that soon), and dark matter is a central concept. On the educational side, the first LAUNCH PAD astronomy workshop for writers recently concluded and was by all means a big success (I'll blog about that very soon). We covered dark matter, and this article, during the workshop.
So the linked article discusses Chandra X-ray observations of "the bullet cluster" which is a collision of two galaxy clusters. The majority of normal, or baryonic, matter as we say, is in the form of very hot gas in clusters. This hot gas emits X-rays that we can see and trace. In the case of the bullet cluster, drag during the collision has impeded the motion of the hot gas. Not the majority of the matter -- dark, non-baryonic matter. That has moved on through just as expected without slowing. And we can trace it by the gravitational lensing of background galaxies. Thus the center of mass of the two clusters has become separated from the center of mass of the hot X-ray gas, which constitutes the bulk of the normal matter. You can't explain away this result by invoking modified Newtonian dynamics, as some try to do for galactic rotation curves and other indirect evidence of dark matter.
So this observation seems like the real deal, the smoking gun if you will, demonstrating the reality of dark matter.