Dark matter near the Sun

Abstract

The amount of dark matter in the disc of the Galaxy at the solar position is determined by comparing the observed distributions of tracer stars with the predictions obtained from different assumptions of how the unseen matter is distributed. The major uncertainties, observational and theoretical, are estimated. For all the observed samples, typical models imply that about half of the mass in the solar vicinity must be in the form of unobserved matter. The volume density of unobserved material near the Sun is about 0.1 M pc -3 ; the corresponding column density is about 30 M pc -2 (1 pc ~ 30857 x 10 12 m). This, so far unseen, material must be in a disc with an exponential scale height of less than 0.7 kpc. All the existing observations are consistent with the unseen disc material being in the form of stars not massive enough to burn hydrogen. It is suggested that the unseen material that is required to hold up the rotation curves of galaxies and to satisfy the virial theorem for clusters of galaxies might also be in the form of low-mass stars.