Heating of galactic gas by dark matter annihilation in ultracompact minihalos

TL;DR

This paper investigates how ultracompact minihalos of dark matter can significantly boost annihilation rates, injecting energy into galactic gas and potentially affecting star formation in Milky Way-like galaxies.

Contribution

It quantifies the impact of dark matter substructure, specifically UCMHs, on galactic gas heating using N-body simulations, revealing potential effects on star formation.

Findings

UCMHs can increase annihilation boost factors to around 10^5.

Presence of UCMHs at 0.1% level can eject gas from the halo.

Energy injection may prevent star formation near the galactic center.

Abstract

The existence of substructure in halos of annihilating dark matter would be expected to substantially boost the rate at which annihilation occurs. Ultracompact minihalos of dark matter (UCMHs) are one of the more extreme examples of this. The boosted annihilation can inject significant amounts of energy into the gas of a galaxy over its lifetime. Here we determine the impact of the boost factor from UCMH substructure on the heating of galactic gas in a Milky Way-type galaxy, by means of N-body simulation. If $1\%$ of the dark matter exists as UCMHs, the corresponding boost factor can be of order $10^5$. For reasonable values of the relevant parameters (annihilation cross section $3\times10^{-26} ~\textrm{cm}^3~ \textrm{s}^{-1}$, dark matter mass 100 GeV, 10% heating efficiency), we show that the presence of UCMHs at the 0.1% level would inject enough energy to eject significant amounts of gas from the halo, potentially preventing star formation within $\sim$1 kpc of the halo centre.