Extragalactic neutrino emission induced by Supermassive and Stellar Mass Black Hole mergers

TL;DR

This paper explores how mergers of supermassive and stellar-mass black holes could produce the high-energy neutrinos detected by IceCube, analyzing merger rates and energy transfer efficiencies.

Contribution

It provides estimates of black hole merger rates and energy transfer fractions necessary for these events to account for the observed neutrino flux.

Findings

SMBBH merger rate between 10^{-7} and 10^{-5} Gpc^{-3} yr^{-1}

Energy transfer to neutrinos during mergers between 10^{-6} and 3×10^{-4}

Stellar-mass BBH merger rate around 10-100 Gpc^{-3} yr^{-1}

Abstract

The recent detections of binary stellar mass black hole mergers by the LIGO and Virgo Collaborations suggest that such mergers are common occurrences. Galaxy mergers further indicate that supermassive black holes in centers of galaxies also merge and are typically expected to have had at least one merger in their lifetime, possibly many. In the presence of a jet, these mergers are almost always accompanied by a change of the jet direction and a connected jet precession motion, leading to interactions of the jet with ambient matter and producing very high-energy particles, and consequently high-energy gamma-rays and neutrinos. In this work, we investigate the possibility under which conditions such mergers could be the sources of the diffuse astrophysical neutrino flux measured by the IceCube Neutrino Observatory. The main free parameters in the calculation concern the frequency of the mergers and the fraction of energy that is transferred from the gravitationally released energy to neutrinos. We show that the merger rate for SMBBHs must lie between $\sim 10^{-7}$ and $10^{-5}$ Gpc$^{-3}$ yr$^{-1}$. The ratio of energy going to neutrinos during such mergers lies then between $\sim 10^{-6} - 3\cdot 10^{-4}$. For stellar mass BBH mergers, the rate needs to be $\sim 10-100$ Gpc$^{-3}$ yr$^{-1}$ and the expected ratio of neutrino to gravitational wave energy lies in a comparable range as for SMBBHs, $\sim 2 \cdot 10^{-5} - 10^{-3}$. These values lie in a reasonable parameter range, so that the production of neutrinos at the level of the detected neutrino flux is a realistic possibility.