GW150914-like Black Holes as Galactic High-Energy Sources

TL;DR

This paper suggests that black holes similar to GW150914 in our galaxy could be significant sources of high-energy cosmic rays, gamma rays, and positrons, with detectable nebulae and implications for electromagnetic counterparts.

Contribution

It introduces a model for black hole jets powered by accretion from the interstellar medium, predicting their role as cosmic-ray accelerators and gamma-ray sources in our galaxy.

Findings

Black hole jets can accelerate cosmic rays up to PeV energies.

Approximately 300 BH jet nebulae could be detectable by CTA.

Accretion from ISM can clear cold material around BHs, affecting merger EM signals.

Abstract

The first direct detections of gravitational waves (GWs) from black hole (BH) mergers, GW150914, GW151226 and LVT151012, give a robust lower limit $\sim 70000$ on the number of merged, highly-spinning BHs in our Galaxy. The total spin energy is comparable to all the kinetic energy of supernovae that ever happened in our Galaxy. The BHs release the spin energy to relativistic jets by accreting matter and magnetic fields from the interstellar medium (ISM). By considering the distributions of the ISM density, BH mass and velocity, we calculate the luminosity function of the BH jets, and find that they can potentially accelerate TeV-PeV cosmic-ray particles in our Galaxy with total power $\sim 10^{37\pm 3}$ erg s$^{-1}$ as PeVatrons, positron factories and/or unidentified TeV gamma-ray sources. Additional $\sim 300$ BH jet nebulae could be detectable by CTA (Cherenkov Telescope Array). We also argue that the accretion from the ISM can evaporate and blow away cold material around the BH, which has profound implications for some scenarios to predict electromagnetic counterparts to BH mergers.