Black Holes in our Galactic Halo: Compatibility with FGST and PAMELA Data and Constraints on the First Stars

TL;DR

This paper investigates whether primordial black holes with dark matter spikes in our galaxy can explain gamma-ray and positron observations, providing constraints on dark matter properties and early star formation history.

Contribution

It introduces a model linking galactic black holes with dark matter spikes to recent FGST and PAMELA data, constraining dark matter annihilation and early star formation.

Findings

Some FGST point sources may be due to dark matter annihilation near black holes.

Limits on dark matter annihilation properties depend on black hole mass and annihilation channel.

FGST data can constrain the fraction of early minihalos hosting the first stars.

Abstract

10 to 10^5 solar mass black holes with dark matter spikes that formed in early minihalos and still exist in our Milky Way Galaxy today are examined in light of recent data from the Fermi Gamma-Ray Space Telescope (FGST). The dark matter spikes surrounding black holes in our Galaxy are sites of significant dark matter annihilation. We examine the signatures of annihilations into gamma-rays, electrons and positrons, and neutrinos. We find that some significant fraction of the point sources detected by FGST might be due to dark matter annihilation near black holes in our Galaxy. We obtain limits on the properties of dark matter annihilations in the spikes using the information in the FGST First Source Catalog as well as the diffuse gamma-ray flux measured by FGST. We determine the maximum fraction of high redshift minihalos that could have hosted the formation of the first generation of stars and, subsequently, their black hole remnants. The strength of the limits depends on the choice of annihilation channel and black hole mass; limits are strongest for the heaviest black holes and annhilation to $b \bar{b}$ and $W^+W^-$ final states. The larger black holes considered in this paper may arise as the remnants of Dark Stars after the dark matter fuel is exhausted and thermonuclear burning runs its course; thus FGST observations may be used to constrain the properties of Dark Stars. Additionally, we comment on the excess positron flux found by PAMELA and its possible interpretation in terms of dark matter annihilation around these black hole spikes.