Astronomers Investigate Galactic Crash

This image combines visible light exposures of galaxy cluster Abell 2744 This image combines visible light exposures of galaxy cluster Abell 2744 taken by the NASA/ESA Hubble Space Telescope and the European Southern Observatory's Very Large Telescope, with X-ray data from NASA's Chandra X-ray Observatory and a mathematical reconstruction of the location of dark matter. Image credit: NASA/ESA/ESO/CXC/STScI/Heidelberg/Bologna
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June 21, 2011

A team of scientists, including Jason Rhodes and Leonidas Moustakas of JPL, has studied the galaxy cluster Abell 2744, nicknamed Pandora's Cluster. They have pieced together the cluster's complex and violent history using telescopes in space and on the ground, including NASA's Hubble Space Telescope and the European Southern Observatory's Very Large Telescope in Chile.

Abell 2744 seems to be the result of a simultaneous pile-up of at least four galaxy clusters, and this complex collision has produced strange effects that had never been seen together before.

The galaxies in the cluster are clearly visible in the Hubble and Very Large Telescope images. Although the galaxies are bright, they make up less than 5 percent of the mass there. The rest is a combination of gas, around 20 percent, which is so hot that it shines only in X-rays, and dark matter, around 75 percent, which is completely invisible. To understand what was going on in the collision, the team needed to map the positions of all three types of matter in Abell 2744.

It seems that the complex collision has separated out some of the hot gas and dark matter so that they now lie apart from each other and from the visible galaxies. One region contains lots of dark matter, but no luminous galaxies or hot gas. A separate ghostly clump of gas has been ejected, which precedes rather than follows the associated dark matter. This puzzling arrangement may be telling astronomers something about how dark matter behaves and how the various ingredients of the universe interact with each other.

Read the full story at http://www.spacetelescope.org/news/heic1111/

Whitney Clavin (818) 354-4673
Jet Propulsion Laboratory, Pasadena, Calif.
whitney.clavin@jpl.nasa.gov

2011-189



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