The Gravitational Spectral Radio Forest: A Signature of Primordial Black Holes

TL;DR

This paper introduces a new gravitational detection method for primordial black holes using hydrogen atoms as quantum sensors, predicting a distinctive radio spectral signature for upcoming surveys.

Contribution

It proposes a novel relativistic effect in hydrogen atoms caused by PBHs, leading to a detectable gravitational spectral radio forest as a unique signature.

Findings

Hydrogen atoms near PBHs exhibit a symmetric splitting of energy states.

The spectral signature appears as a 9.9 GHz absorption line redistributed over a 2 GHz bandwidth.

Active accretion enhances the absorption spectrum, improving detectability.

Abstract

We propose a novel gravitational signature to detect Primordial Black Hole (PBH) dark matter by treating interstellar hydrogen as a quantum sensor for spacetime curvature. Focusing on H II regions, we demonstrate that the Riemann tidal tensor of an \emph{asteroid-mass} PBH induces a symmetric splitting of the $2P_{3/2}$ state in bound hydrogen atoms. This relativistic effect redistributes $9.9\,\mathrm{GHz}$ absorption line into a gravitational spectral radio forest with a bandwidth $\sim 2\,\mathrm{GHz}$. By accounting for active accretion of Hydrogen atoms and the resulting density-squared emission measure within the Bondi radius, we find a relatively enhanced absorption spectrum. This feature presents a concrete, high-contrast target for upcoming radio-surveys to constrain PBH populations in the dark matter sector.