No WIMP Mini-Spikes in Dwarf Spheroidal Galaxies

TL;DR

This paper uses Fermi LAT data and simulations to constrain the presence of black hole-induced dark matter spikes in dwarf spheroidal galaxies, challenging certain black hole formation scenarios and WIMP dark matter models.

Contribution

It provides the first stringent observational limits on mini-spikes in dwarf galaxies and tests specific black hole formation scenarios against WIMP dark matter.

Findings

Limits on black hole masses in dwarf galaxies based on gamma-ray data

Exclusion of certain black hole formation scenarios at 84% confidence level

Constraints on WIMP dark matter properties from non-detection of mini-spikes

Abstract

The formation of black holes inevitably affects the distribution of dark and baryonic matter in their vicinity, leading to an enhancement of the dark matter density, called spike, and if dark matter is made of WIMPs, to a strong enhancement of the dark matter annihilation rate. Spikes at the center of galaxies like the Milky Way are efficiently disrupted by baryonic processes, but mini-spikes can form and survive undisturbed at the center of dwarf spheroidal galaxies. We show that Fermi LAT satellite data allow to set very stringent limits on the existence of mini-spikes in dwarf galaxies: for thermal WIMPs with mass between 100 GeV and 1 TeV, we obtain a maximum black hole mass between 100 and 1000 $M_\odot$, ruling out black holes masses extrapolated from the M-{\sigma} relationship in a large region of the parameter space. We also performed Monte Carlo simulations of merger histories of black holes in dwarf spheroidals in a scenario where black holes form from the direct collapse of primordial gas in early halos, and found that this specific formation scenario is incompatible at the 84% CL with dark matter being in the form of thermal WIMPs.