White dwarfs and dark matter.

Based on the identification of 38 white dwarfs with halo kinematics, in a survey covering 10% of the sky near the south galactic pole, Oppenheimer et al. (1) argued that at least 2% of the dark matter in the Milky Way galaxy has now been detected directly. Put into context, the Oppenheimer et al. result implies that the stellar remnant mass of the halo may be comparable to that of the entire disk of the galaxy. If true, that finding has crucial consequences for understanding the formation and evolution of the Milky Way. Careful examination of the results of Oppenheimer et al., however, leads us to conclude that they have overestimated that the density of white dwarfs with halo kinematics. Oppenheimer et al. (1) derived their local white dwarf density n via the 1/Vmax technique (2). The equation that applies for a survey covering 10% of the sky is