16th March 2009 - 04:01 AM
NASA's Hubble Space Telescope has uncovered new evidence that galaxies are embedded in and protected by halos of dark matter, the invisible form of matter that accounts for most of the universe's mass.
Dark matter is invisible and nobody even knows what it is, but it is evident by the fact that galaxies hold together at all. Some unseen substance lurks in space — concentrated in galaxies — and generated gravity in amounts well beyond the visible matter.
Peering into the tumultuous heart of the nearby Perseus galaxy cluster (located 250 million light-years away), Hubble discovered a large population of small galaxies that have remained intact while larger galaxies around them are being ripped apart by the gravitational pull of neighboring galaxies.
"We were surprised to find so many dwarf galaxies in the core of this cluster that were so smooth and round and had no evidence at all of any kind of disturbance," said astronomer Christopher Conselice of the University of Nottingham in England, and leader of the Hubble observations.
"These dwarfs are very old galaxies that have been in the cluster a long time. So if something was going to disrupt them, it would have happened by now. They must be very, very dark matter-dominated galaxies."
Full at http://www.space.com/scienceastronomy/0903...ark-matter.html