Powerful Cosmic Collision Creates Divorce of Matter

A violent merger between two galaxy clusters appears to have split ordinary matter from dark matter.

NASA's Hubble Space Telescope and Chandra X-ray Observatory show dark matter from each cluster appearing to pass through the cosmic mess unscathed, leaving ordinary matter behind in the galactic pileup.

Nobody knows what dark matter is, and it has never been directly detected. Its mysterious presence is known by observations of how it affects regular matter or light, which can be bent by gravity. Astronomers say dark matter makes up as much as 90 percent of all matter in the universe.

Hubble helped map out the distribution of dark matter in the collision by seeing the bending of light around areas with dark matter. Chandra spotted X-rays from the hot gas that makes up the bulk of ordinary matter in the clusters.

The latest observations of the MCSJ0025 cluster appear to to back up earlier findings from another cosmic collision in what's called the Bullet Cluster. That impact also tore normal and dark matter apart and demonstrated the forcible separation of ordinary and dark matter.

The same separation suggests that dark-matter particles interact only weakly outside of gravity's influence, given that they passed by one another inside the collision zone with little visible effect.

The research team also estimated the mass distribution of both dark and ordinary matter by using Hubble's visible-light images. Each cluster boasted almost a quadrillion times the mass of the sun.

Results from the new study of collision, a scene that's about 5.7 billion light-years away and involved speeds of millions of miles per hour, are detailed in an upcoming issue of The Astrophysical Journal.

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