AI Insight
This paper proposes a new method to detect primordial black holes (PBHs) as candidates for dark matter by using interstellar hydrogen in ionized hydrogen regions (H II regions) as a quantum sensor for spacetime curvature. The authors show that the tidal gravitational field of an asteroid-mass PBH causes a symmetric splitting of the hydrogen 2P(3/2) energy state, redistributing a 9.9 GHz absorption line into a broadened spectral feature spanning roughly 2 GHz, which they call the gravitational spectral radio forest. Accounting for hydrogen accretion within the Bondi radius further enhances the absorption signal, making it potentially detectable by next-generation radio telescope surveys.
Why it matters
If confirmed observationally, this technique would provide a concrete and independent method to constrain the abundance and mass distribution of primordial black holes in the dark matter sector, a longstanding open problem in cosmology and astrophysics.
arXiv:2605.13042v1 Announce Type: cross
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.
Source: The Gravitational Spectral Radio Forest: A Signature of Primordial Black Holes