Solar Mass Objects?

If the dark matter in galactic halos is made up of compact, macroscopic objects (MO), such as black holes with M M O >> M stars , gravitational scattering will lead to kinematic heating of the stars. Observational constraints on the amount of heating in the disk of the Milky Way put upper limits on M M O < ∼ 10 6.3 M ⊙. We find limits that are three orders of magnitude more stringent by examining the heating limits in low mass stellar systems, where higher densities of dark matter and lower relative velocities would destroy stellar disks or disperse the stars in less than a billion years. Limits on M M O are derived from two nearby dwarf galaxies, dominated by dark matter: the presence of a flat stellar disk in the dwarf spiral galaxy DDO 154 is shown to imply M M O < ∼ 7 × 10 5 M ⊙ , comparable to the limits derived for the Galactic disk. However, the structure and kinematics of the Local Group member GR8 yield a limit of M M O < ∼ 6 × 10 3 M ⊙. We also examine the possibility that the local disk heating is done by compact clusters of brown dwarfs rather than black holes. Such clusters could dissolve in the higher density halos of small galaxies. While theoretical arguments have been presented for such clusters, they should have been detected in the IRAS point source catalog. If the properties of the dark matter are universal these results preclude the dominance of dark matter constituents in the cosmologically interesting mass range ∼ 10 6 M ⊙ and limit them to M M O < ∼ 10 3.7 M ⊙. These results also rule out massive compact halo objects as significant contributors to the kinematic heating of the Galactic disk. I. Introduction The self-gravity of many astrophysical systems is clearly dominated by dark matter. Starting from Zwicky's original claim of dark matter in clusters of galaxies, evidence for dark matter has been found on both larger scales and on smaller, galactic scales (see e.g. Trimble 1987 and Ashman 1992 for reviews). While the existence of dark matter has been clearly established, its nature is still unknown. Candidates currently under discussion range from postulated elementary particles to compact objects with masses vastly greater than stellar masses–a mass range of 10 70 ! Compelling cases have …