# Inferences about supernova physics from gravitational-wave measurements: GW151226 spin misalignment as an indicator of strong black-hole natal kicks

## TL;DR

This paper uses gravitational-wave data from GW151226 to infer that the black hole's spin misalignment suggests it received a strong natal kick during stellar collapse, challenging existing supernova models.

## Contribution

It introduces a method to constrain black hole natal kicks using gravitational-wave spin measurements, revealing larger kicks than previously assumed.

## Key findings

- Black hole in GW151226 likely received a natal kick >50 km/s.
- Such kicks are larger than those in standard supernova models.
- Spin misalignment indicates significant black hole natal kicks.

## Abstract

The inferred parameters of the binary black hole GW151226 are consistent with nonzero spin for the most massive black hole, misaligned from the binary's orbital angular momentum. If the black holes formed through isolated binary evolution from an initially aligned binary star, this misalignment would then arise from a natal kick imparted to the first-born black hole at its birth during stellar collapse. We use simple kinematic arguments to constrain the characteristic magnitude of this kick, and find that a natal kick $v_k \gtrsim 50$ km/s must be imparted to the black hole at birth to produce misalignments consistent with GW151226. Such large natal kicks exceed those adopted by default in most of the current supernova and binary evolution models.