Two teams of astronomers using the Hubble Space Telescope have overturned several decades of conjecture and theory by ruling out the possibility that small, dim stars make up most of the mass in the universe. Until now, small stars known as faint red dwarfs were considered ideal candidates for the so-called "dark matter" that is believed to account for more than 90 percent of the mass of the universe. All visible celestial objects, such as planets, stars and galaxies, are believed to account for only 10 percent of the mass of the universe. The rest of the "missing mass" is presumably invisible because it does not emit or reflect light, or the light is too feeble to be detected. But dark matter can be indirectly detected due to its gravitational influence on other visible objects. According to Bacall, professor of natural science at the Institute of Advanced Study in Princeton, New Jersey and leader of one of the teams, the nature of dark matter, and its abundance, are among the most important questions in modem cosmology today. The ultimate fate of the universe will be determined by the amount of dark matter present. If there is not enough dark matter to bind the universe together gravitationally, it could continue expanding forever. If there is enough mass to hold the universe together gravitationally, the universe may slow down its expansion, come to a halt and begin to contract and eventually collapse.