# A "nu" look at gravitational waves: The black hole birth rate from neutrinos combined with the merger rate from LIGO

## TL;DR

This paper explores how future neutrino and gravitational wave observations can jointly constrain the rate of black hole formation and mergers, providing insights into stellar evolution and compact object populations.

## Contribution

It introduces a method to combine neutrino background measurements with gravitational wave data to estimate the black hole merger fraction, accounting for uncertainties in neutrino emission models.

## Key findings

- Black hole birth rate can be constrained using DSNB measurements.
- The black hole merger fraction $oldsymbol{psilon}$ can be estimated within a specific range.
- Combining neutrino and gravitational wave data improves understanding of black hole formation.

## Abstract

We make projections for measuring the black hole birth rate from the diffuse supernova neutrino background (DSNB) by future neutrino experiments, and constrain the black hole merger fraction $\epsilon$, when combined with information on the black hole merger rate from gravitational wave experiments such as LIGO. The DSNB originates from neutrinos emitted by all the supernovae in the Universe, and is expected to be made up of two components: neutrinos from neutron-star-forming supernovae, and a sub-dominant component at higher energies from black-hole-forming "unnovae". We perform a Markov Chain Monte Carlo analysis of simulated data of the DSNB in an experiment similar to Hyper-Kamiokande, focusing on this second component. Since all knowledge of the neutrino emission from unnovae comes from simulations of collapsing stars, we choose two sets of priors: one where the unnovae are well-understood and one where their neutrino emission is poorly known. By combining the black hole birth rate from the DSNB with projected measurements of the black hole merger rate from LIGO, we show that the fraction of black holes which lead to binary mergers observed today $\epsilon$ could be constrained to be within the range $2 \cdot 10^{-4} \leq \epsilon \leq 3 \cdot 10^{-2}$ at $3 \sigma$ confidence, after ten years of running an experiment like Hyper-Kamiokande.