| Description: | Roughly speaking, there are two types of galaxies: those where stars are forming (so-called spiral galaxies like our own Milky Way) and galaxies without any star formation (so-called elliptical galaxies). It has always been thought that the reason for this difference is the lack of gas in elliptical galaxies: stars form from gas and if there is no gas, no stars will form.... However, several elliptical galaxies have been discovered by us (using the Australia Telescope Compact Array) that are very gas rich. The difference with the star forming gas-rich spiral galaxies is that the newly discovered gas disks have low gas density. In fact, the density is so low that no stars can form from the gas. So it looks like that the reason that (at least some) ellipticals do not form stars is not the lack of gas, but the low density of their gas reservoirs. Since nothing seems to happen in these gas disks, they must be very old and are a fossil record of the way the galaxies formed. For more details see the paper that will soon appear in Astronomy & Astrophysics: Oosterloo et al. http://arxiv.org/pdf/astro-ph/0701716 |
