Topic: Mapping the Dark Matter

[sam]

That ghostly haze is dark matter — or at least, an impression of the gravitational field created by the dark matter. This is galaxy cluster Abell 1689, in the constellation Virgo. (We feel compelled to add that information, in case you’re going to go looking for it in the night sky tonight or something.) It’s easy to see that the images of many of the galaxies have been noticeably warped by passing through the gravitational field of the cluster, a phenomenon known as strong gravitational lensing. This cluster has been studied for a while  using strong lensing. The idea is that the detailed distribution of dark matter affects the specific ways in which different background images are distorted (similar to what was used to analyze the Bullet Cluster). Astronomers use up massive amounts of computer time constructing different models and determining where the dark matter has to be to distort the galaxies in just the right way. Now Dan Coe and collaborators have made an unprecedentedly high-precision map of where the dark matter is (paper here).

http://blogs.discovermagazine.com/cosmicvariance/2010/11/13/mapping-the-dark-matter/

[Clive]

I think we saw low resolution pictures of the 'invisible' dark matter around this cluster a few months back but this is a much better picture.  Some of those galaxies appear very distorted indeed! 

[sam]

good old gravitational lensing.