21-cm constraints on spinning primordial black holes

TL;DR

This paper uses the global 21-cm hydrogen signal during the cosmic dark ages to place the most stringent constraints yet on the abundance and spin of primordial black holes in a specific mass range, surpassing previous CMB limits.

Contribution

It introduces novel constraints on spinning primordial black holes using 21-cm observations, extending the mass range and considering various distribution models.

Findings

21-cm data provides more stringent PBH constraints than CMB data.

Higher spin PBHs are more strongly constrained.

Excludes certain PBH masses and spins as dark matter candidates.

Abstract

Hawking radiation from primordial black holes (PBH) can ionize and heat up neutral gas during the cosmic dark ages, leaving imprints on the global 21-cm signal of neutral hydrogen. We use the global 21-cm signal to constrain the abundance of spinning PBHs in mass range of $[2 \times 10^{13}, 10^{18}]$ grams. We consider several extended PBH distribution models. Our results show that 21-cm can set the most stringent PBH bounds in our mass window. Compared with constraints set by {\it Planck} cosmic microwave background (CMB) data, 21-cm limits are more stringent by about two orders of magnitudes. PBHs with higher spin are typically more strongly constrained. Our 21-cm constraints for the monochromatic mass distribution rule out spinless PBHs with initial mass below $1.5 \times 10^{17}\ \r{g}$, whereas extreme Kerr PBHs with reduced initial spin of $a_0=0.999$ are excluded as the dominant dark matter component for masses below $6 \times 10^{17}\ \r{g}$. We also derived limits for the log-normal, power-law and critical collapse PBH mass distributions.