  The very first stars likely formed from metal-free, molecular hydrogen-cooled
gas at the centers of dark matter minihalos. Prior to nuclear fusion, these
stars may have been supported by dark matter heating from annihilations in the
star, in which case they could have grown to be quite massive before collapsing
to black holes. Many remnant black holes and their surrounding dark matter
density spikes may be part of our Milky Way halo today. Here we explore the
gamma-ray signatures of dark matter annihilations in the dark matter spikes
surrounding these black holes for a range of star formation scenarios, black
hole masses, and dark matter annihilation modes. Data from the Fermi Gamma-Ray
Space Telescope are used to constrain models of dark matter annihilation and
the formation of the first stars.
