http://www.nasa.gov/home/hqnews/2006/aug/HQ_M06128_dark_matter.html press conference Monday 21 August CHANDRA team has been watching the highspeed collision of two clusters of galaxies they can see the GAS of the clusters colliding and getting hot so it radiates Xrays they may have also seen evidence (lensing) of some of the dark matter passing right through and forming a lobe on the other side this could be a case where dark matter really acts like a kind of MATTER and not like an effect of modifying gravity as in MOND or relativisitic MOND. Baez TWF 238 http://math.ucr.edu/home/baez/week238.html discusses this and gives links to previous CHANDRA papers. Also described at Baez blog http://golem.ph.utexas.edu/category/2006/08/dark_matter_in_the_bullet_clus.html here's an abstract: http://www.cosis.net/abstracts/COSPAR2006/02655/COSPAR2006-A-02655.pdf Dark matter and the bullet cluster M. Markevitch (1), S. Randall (1), D. Clowe (2), A. Gonzalez (3), M. Bradac (4) (1) Harvard-Smithsonian Center for Astrophysics, (2) University of Arizona, (3) University of Florida, (4) KIPAC, Stanford University " 1E0657-56, the "bullet cluster", is a merger with a uniquely simple geometry. From the long Chandra X-ray observation which revealed a classic bow shock in front of a small subcluster, we can derive the velocity of the subcluster and its direction of motion. Recent accurate weak and strong lensing total mass maps clearly show two merging subclusters, including the host of the gas bullet seen in X-rays. This cluster provided the first direct, model-independent proof of the dark matter existence (as opposed to any modified gravity theory) and a direct constraint on the self-interaction cross-section of the dark matter particles. I will review these and other related results." I think even better is this set of lecture slides from Maxim Markevitch By a strange coincidence i have been SCUBA diving for several days in the same boat party with Maxim, in the Carribean these pictures are great the presentation is 2) Maxim Markevitch, Scott Randall, Douglas Clowe, and Anthony H. Gonzalez, Insights on physics of gas and dark matter from cluster mergers http://cxc.harvard.edu/symposium_2005/proceedings/theme_energy.html#abs23 you click on the PDF http://cxc.harvard.edu/symposium_2005/proceedings/files/markevitch_maxim.pdf the pictures show the two clusters colliding, and the very hot ball of gas (ordinary matter) and then they show the LENSING BACKGROUND mapping the levelcurves of the dark matter density to show that the dark matter has passed through----and so has been spatially separated from the gas. so it is not just a mondian gravitational effect OF the gas which would be located around the gas. if this all checks out it would seem to be an observation of dark matter being a real substance ============ I got help from matt.o editing this post. thx!