# Observational evidence for stellar mass binary black holes and their coalescence rate

## TL;DR

This paper reviews binary black hole formation, analyzes a specific system IC10 X-1, and estimates a high coalescence and detection rate, suggesting the first gravitational wave detection may be from binary black holes.

## Contribution

It provides observational evidence for stable mass transfer in binary black hole formation and estimates the coalescence rate, highlighting the likelihood of detecting black hole mergers first.

## Key findings

- IC10 X-1 can form a binary black hole system.
- Estimated coalescence rate density is 0.06 Mpc^{-3} Myr^{-1}.
- Detection rate for LIGO/VIRGO is approximately 0.69 per year.

## Abstract

We review the formation scenarios for binary black holes, and show that their coalescence rate depends very strongly on the outcome of the second mass transfer. However, the observations of IC10 X-1, an binary with a massive black hole accreting from a Wolf-Rayet star proves that this mass transfer can be stable. We analyze the future evolution of IC10 X-1 and show that it is very likely to form a binary black hole system merging in a few Gyrs. We estimate the coalescence rate density of such systems to be $ 0.06 {\rm Mpc}^{-3} {\rm Myr}^{-1}$, and the detection rate for the current LIGO/VIRGO of $ 0.69 {\rm yr}^{-1} $, a much higher value than the expected double neutron star rate. Thus the first detection of a gravitational wave source is likely to be a coalescence of a binary black hole.