spacetoday.net: Stars, galaxies shed light on dark matter

Posted: Tue, Jun 1, 2004, 7:54 PM ET (2354 GMT)
SIRTF illustration (NASA/JPL/Caltech)

The discovery of the faintest galaxy ever seen, as well as a nearby low-mass star, have provided astronomers with new insights into the distribution of dark matter around galaxies. One team of astronomers reported Monday the discovery of a a faint galaxy in the vicinity of the large nearby galaxy of Andromeda. The satellite galaxy Andromeda IX, first seen in data from the Sloan Digital Sky Survey, is twice as dim as the previous record-holder for faintest galaxy and 100,000 times dimmer than the Milky Way. The discovery may solve the "missing satellite" problem associated with models of dark matter distribution: those models predicted the existence of 10 to 100 times as many satellite galaxies as had previously been seen. Astronomers think such galaxies may indeed exist but have been too faint to be detected before. In a separate study, astronomers using the Spitzer Space Telescope have determined that a potential concentration of dark matter in the Milky Way is just an ordinary star. Spitzer observations of an object first detected in a microlensing search for dark matter determined that the object was not a distant concentration of dark matter but instead a low-mass star just 1,500 light-years away. The discovery may explain why the original microlensing search detected far more potential dark matter objects than expected.