# Research Note: The Expected Spins of Gravitational Wave Sources With Isolated Field Binary Progenitors

## TL;DR

This paper investigates the expected spin distributions of black holes from isolated binary progenitors, suggesting a bi-modal distribution that aligns with current LIGO observations and contrasting with high-mass X-ray binary systems.

## Contribution

It introduces a theoretical framework predicting the spin outcomes of black holes from field binaries, highlighting the potential bi-modal distribution of GW source spins.

## Key findings

- LIGO GW sources likely have low or maximal spins, leading to a bi-modal distribution.
- Current HMXB systems show different spin characteristics, implying different formation channels.
- The spin distribution can distinguish between different astrophysical origins of compact binaries.

## Abstract

We explore the consequences of dynamical evolution of field binaries composed of a primary black hole (BH) and a Wolf-Rayet (WR) star in the context of gravitational wave (GW) source progenitors. We argue, from general considerations, that the spin of the WR-descendent BH will be maximal in a significant number of cases due to dynamical effects. In other cases, the spin should reflect the natal spin of the primary BH which are currently theoretically unconstrained. We argue that the three currently published LIGO systems (GW150914, GW151226, LVT151012) suggest that this spin is small. The resultant effective spin distribution of gravitational wave sources should thus be bi-model if this classic GW progenitor channel is indeed dominant. While this is consistent with the LIGO detections thus far, it is in contrast to the three best-measured high-mass x-ray binary (HMXB) systems. A comparison of the spin distribution of HMXBs and GW sources should ultimately reveal whether or not these systems arise from similar astrophysical channels.