CAN THE DARK-MATTER BE-10(6) M-CIRCLE-DOT OBJECTS

If the dark matter in galactic halos is made up of compact. macroscopi c objects (MOs), such as black holes With M(MO) much greater than M(st ars), gravitational scattering will lead to kinematic heating of the s tars. Observational constraints on the amount of heating in the disk o f the Milky Way put upper limits on M(MO) less than or similar 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 hig her densities of dark matter and lower relative velocities would destr oy stellar disks or disperse the stars in less than a billion years. L imits on M(MO) are derived from two nearby dwarf galaxies, dominated b y an extended dark matter halo: the presence of a flat stellar disk in the dwarf spiral galaxy DDO 154 is shown to imply M(MO) less than or similar 7 x 10(5) M., comparable to the limits derived for the Galacti c disk, However, the structure and kinematics of the Local Group membe r GR 8 yield a limit of M(MO) less than or similar 6 x 10(3) M.. We al so examine the possibility that the local disk heating is done by comp act clusters of brown dwarfs rather than black holes. Such clusters co uld dissolve in the higher density halos of small galaxies. While theo retical arguments have been presented for such clusters, they should h ave 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 ra nge approximately 10(6) M. and limit them to M(MO) less than or simila r 10(3.7) M.. These results also rule out massive compact halo objects as significant contributors to the kinematic heating of the Galactic disks.