The Sensitivity of Future Gamma-Ray Telescopes to Primordial Black Holes

TL;DR

Future MeV gamma-ray telescopes like e-ASTROGAM or AMEGO could significantly improve constraints on primordial black holes in the mass range of about 6×10^{15} to 2×10^{17} grams, and potentially detect Hawking radiation linked to the 511 keV excess.

Contribution

This paper evaluates the potential of upcoming gamma-ray telescopes to set new constraints on primordial black holes and to detect Hawking radiation from them.

Findings

Future telescopes could improve constraints by two orders of magnitude.

They could detect Hawking radiation if the 511 keV excess is due to black holes.

Potential to measure black hole abundance and mass distribution.

Abstract

The strongest existing constraints on primordial black holes with masses in the range of $m_{\rm BH} \sim 10^{15}-10^{17} \, {\rm g}$ have been derived from measurements of the local cosmic-ray electron-positron flux by Voyager 1, and MeV-scale gamma-ray observations of the Inner Galaxy by COMPTEL and INTEGRAL. In this paper, we evaluate the sensitivity of future MeV-scale gamma-ray telescopes such as e-ASTROGAM or AMEGO to Hawking radiation. We show that such an instrument would be able to provide the strongest constraints on black holes in the mass range of $m_{\rm BH} \sim (0.6-20) \times 10^{16} \, {\rm g}$, typically exceeding current constraints by approximately two orders of magnitude. In scenarios in which the observed 511 keV excess is the result of Hawking radiation, we find that e-ASTROGAM or AMEGO would not only be able to detect the Hawking radiation from the Inner Galaxy, but could precisely measure the abundance and mass distribution of the black holes responsible for this signal.