Direct Detection of Galactic Halo Dark Matter
B. R. Oppenheimer,1*
N. C. Hambly,2
A. P. Digby,2
S. T. Hodgkin,3
D. Saumon4
The Milky Way galaxy contains a large, spherical component which is
believed to harbor a substantial amount of unseen matter. Recent observations indirectly suggest that as much as half of this "dark matter" may be in the form of old, very cool white dwarfs, the remnants of an ancient population of stars as old as the galaxy itself.
We conducted a survey to find faint, cool white dwarfs with large space
velocities, indicative of their membership in the galaxy's spherical
halo component. The survey reveals a substantial, directly observed
population of old white dwarfs, too faint to be seen in previous
surveys. This newly discovered population accounts for at least 2 percent of the halo dark matter. It provides a natural explanation for
the indirect observations, and represents a direct detection of
galactic halo dark matter.
1 Astronomy Department, University of
California-Berkeley, Berkeley, CA 94720-3411, USA.
2 Institute for Astronomy, University of Edinburgh,
Royal Observatory, Blackford Hill, Edinburgh, EH9 3HJ, UK.
3 Institute of Astronomy, Cambridge University,
Madingley Road, Cambridge, CB3 0HA, UK.
4 Department
of Physics and Astronomy, Vanderbilt University, Nashville, TN 37235, USA.
*
To whom correspondence should be addressed. E-mail:
bro{at}astron.berkeley.edu
