Nearly 70 years ago, astronomer Fritz Zwicky observed that clusters of galaxies do not hold enough visible stars to explain their rotation. He subsequently proposed that the missing mass in fact resides in the galaxies but does not radiate any light. Ever since then, however, the identity of this so-called dark matterwhich is estimated to account for about 95 percent of the mass of galaxies such as our ownhas eluded researchers. Findings announced today in the journal Science, however, are throwing light on the mysterious matter. According to the new study, as much as 35 percent of the dark matter in our galaxy may be composed of dead stars.
Scrutinizing digitized images of the southern sky, Ben R. Oppenheimer of the University of California at Berkeley and his colleagues discovered 38 previously unnoticed cool white dwarfsfaint stellar remnants dating back some 10 to 13 billion years agoin a small portion of the halo of dark matter encircling the Milky Way. If this density of white dwarfs accurately reflects that of the rest of the halo, then they can account for at least 3 percent and perhaps up to 35 percentof the galactic dark matter.
The significance of the new findings could be far-reaching. "This research is not just about white dwarfs and dark matter. It also has implications for the star formation history of the galaxy, probably even before the disk itself formed," team member Didier Saumon of Vanderbilt University remarks. "There is much to learn about how galaxies form, and about how stars form in the process, from studying this population of white dwarfs."
ABOUT THE AUTHOR(S)
Kate Wong is a senior editor for evolution and ecology at Scientific American. Follow her on Twitter @katewong Credit: Nick Higgins