Constraining the population of intermediate mass black holes by gamma-ray data of the Fornax cluster

TL;DR

This study uses gamma-ray data from the Fornax cluster to place constraints on the abundance of intermediate mass black holes, including primordial black holes, by analyzing dark matter annihilation signals.

Contribution

It provides new upper limits on the population of IMBHs and PBHs based on gamma-ray observations and dark matter annihilation models.

Findings

IMBHs and PBHs are sub-dominant compared to baryons and dark matter.

Upper limit on IMBH-to-baryon ratio is approximately 7×10⁻⁴ for dark matter mass ≤ 10 TeV.

Dark matter annihilation signals constrain IMBH abundance.

Abstract

Recent studies of merging black holes suggest that the cosmological mass fraction of primordial black holes (PBHs) is not completely negligible. The mass of a PBH can be as massive as an intermediate mass black hole (IMBH). In this article, we assume that dark matter particles are thermal relic particles and they can self-annihilate. The dark matter around an IMBH may have formed a density spike so that the rate of dark matter annihilation would be greatly enhanced. Using the gamma-ray data of the Fornax cluster and assuming merging events in the cluster are not important, we show that the amount of IMBHs (including PBHs) is very sub-dominant compared with the amount of baryons and dark matter. The upper limit on the IMBH-to-baryon ratio is $\sim 7\times 10^{-4}$ for $m_{\rm DM} \le 10$ TeV.