March 12, 2009: When it comes to finding dark matter in space, astronomers need to go on sort of a ghost hunt. Dark matter can't be directly seen or isolated in a laboratory. Yet it makes up the bulk of the matter in the universe. It is the invisible scaffolding for the formation of stars and galaxies. Dark matter is not made of the same stuff that stars, planets, and people are made of. That stuff is normal "baryonic" matter, consisting of electrons, protons, and neutrons. For 80 years astronomers have known about dark matter's "ghostly" pull on normal matter. They've known that without the gravitational "glue" of dark matter galaxy clusters would fly apart, and even galaxies would have a hard time holding together.
Now the Hubble Space Telescope has uncovered a strong new line of evidence that galaxies are embedded in halos of dark matter. Peering into the tumultuous heart of the nearby Perseus galaxy cluster, Hubble's sharp view resolved a large population of small galaxies that have remained intact while larger galaxies around them are being ripped apart by the gravitational tug of other galaxies. The dwarfs' "invisible shield" is a robust halo of dark matter that keeps them intact despite a several-billion-year-long bumper-car game inside the massive galaxy cluster.See the rest: