Light Axion Emission and the Formation of Merging Binary Black Holes

TL;DR

This paper investigates how light axion emission affects the formation of binary black holes, showing it can prevent mergers with black holes in the lower mass gap, thus potentially explaining observed mass gaps in gravitational wave data.

Contribution

It demonstrates that light axion emission can alter stellar evolution, preventing certain black hole binary formations and explaining the observed mass gap in gravitational wave observations.

Findings

Light axion emission prevents formation of low-mass gap black hole binaries.

Axions with specific couplings can influence stellar mass transfer and common envelope evolution.

Results suggest a possible explanation for the observed black hole mass gap in gravitational wave data.

Abstract

We study the impact of stellar cooling due to light axion emission on the formation and evolution of black hole binaries, via stable mass transfer and the common envelope scenario. We find that in the presence of light axion emission, no binary black hole mergers are formed with black holes in the lower mass gap ($\rm M_{\rm BH} < 4 M_\odot $) via the common envelope formation channel. In some systems, this happens because axions prevent Roche lobe overflow. In others, they prevent the common envelope from being ejected. Our results apply to axions with couplings $ g_{a \gamma} \gtrsim 10^{-10}\, \rm GeV^{-1}$ (to photons) or $\alpha_{ae} \gtrsim 10^{-26} $ (to electrons) and masses $ m_a \ll 10 \, \rm keV$. Light, weakly coupled particles may therefore apparently produce a mass gap $\rm 2 M_\odot < M_{\rm BH} < 4 M_\odot $ in the LIGO/Virgo/KAGRA data, when no mass gap is present in the stellar remnant population.