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Title:
Can the Dark Matter be 10 6 Solar Mass Objects?
Authors:
Rix, Hans-Walter; Lake, George
Publication:
Astrophysical Journal Letters v.417, p.L1 (ApJL Homepage)
Publication Date:
11/1993
Origin:
APJ; KNUDSEN; NED
Astronomy Keywords:
COSMOLOGY: DARK MATTER, GALAXIES: KINEMATICS AND DYNAMICS
DOI:
10.1086/187079
Bibliographic Code:
1993ApJ...417L...1R

Abstract

If the dark matter in galactic halos is made up of compact, macroscopic objects (MOs), such as black holes with M_MO_ > 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_MO_ <~ 10^6.3^ M_sun_. 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_MO_ are derived from two nearby dwarf galaxies, dominated by 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_ <~ 7 X 10^5^ M_sun_, comparable to the limits derived for the Galactic disk. However, the structure and kinematics of the Local Group member GR 8 yield a limit of M_MO_ <~ 6 x 10^3^ M_sun_. 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_sun_ and limit them to M_MO_ <~ 10^3.7^ M_sun_. These results also rule out massive compact halo objects as significant contributors to the kinematic heating of the Galactic disks.

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