Bounds on the Mass and Abundance of Dark Compact Objects and Black Holes in Dwarf Spheroidal Galaxy Halos

We establish new dynamical constraints on the mass and abundance of compactobjects in the halo of dwarf spheroidal galaxies. In order to preservekinematically cold the second peak of the Ursa Minor dwarf spheroidal (UMidSph) against gravitational scattering, we place upper limits on the density ofcompact objects as a function of their assumed mass. The mass of the darkmatter constituents cannot be larger than 1000 solar masses at a halo densityin UMi's core of 0.35 solar masses/pc^3. This constraint rules out a scenarioin which dark halo cores are formed by two-body relaxation processes. Ourbounds on the fraction of dark matter in compact objects with masses >3000solar masses improve those based on dynamical arguments in the Galactic halo.In particular, objects with masses $\sim 10^{5}$ solar masses can comprise nomore than a halo mass fraction $\sim 0.01$. Better determinations of thevelocity dispersion of old overdense regions in dSphs may result in morestringent constraints on the mass of halo objects. For illustration, if thepreliminary value of 0.5 km/s for the secondary peak of UMi is confirmed,compact objects with masses above $\sim 100$ solar masses could be excludedfrom comprising all its dark matter halo.Comment: 6 pages, 2 figures, accepted for publication in ApJ Letter