Constraining spinning primordial black holes with global 21-cm signal

TL;DR

This paper uses the global 21-cm signal at redshift ~17 to set upper bounds on the fraction of dark matter that can be in the form of spinning primordial black holes, showing that spin enhances constraints.

Contribution

It introduces a method to constrain spinning primordial black holes using the 21-cm absorption feature, improving bounds compared to non-spinning cases.

Findings

Stronger constraints on spinning PBHs than non-spinning ones.

Allowed PBH mass can be as low as 6.7 x 10^17 g for extremal spins.

Provides the most stringent lower mass bound from 21-cm data.

Abstract

We study the upper projected bounds on the dark matter fraction in the form of the primordial black holes (PBHs) with a non-zero spin by using the absorption feature in the global 21-cm signal at redshift z ~ 17. The mass and spin are fundamental properties of a black hole, and they can substantially affect the evaporation rate of the black hole. The evaporating black hole can inject energy into the intergalactic medium and heat the gas. Subsequently, it can modify the absorption amplitude in the global 21-cm signal. Therefore, the absorption feature in the 21-cm signal can provide a robust bound on PBHs. We analyse the projected constraints on the dark matter fraction in the form of both spinning and non-spinning PBHs. The constraints are more stringent for spinning PBHs than non-spinning ones. We also compare these bounds with other observations and find the most stringent lower constraint on PBHs mass, which is allowed to constitute the entire dark matter to 6.7 x 10^17 g for extremal spinning PBHs.