The Low Effective Spin of Binary Black Holes and Implications for Individual Gravitational-wave Events
Abstract
While the Advanced LIGO and Virgo gravitational-wave (GW) experiments now regularly observe binary black hole (BBH) mergers, the evolutionary origin of these events remains a mystery. Analysis of the BBH spin distribution may shed light on this mystery, offering a means of discriminating between different binary formation channels. Using the data from Advanced LIGO and Virgo's first and second observing runs, here we seek to carefully characterize the distribution of effective spin ${\chi }_{\mathrm{eff}}$ among BBHs, hierarchically measuring the distribution's mean μ and variance σ2 while accounting for selection effects and degeneracies between spin and other black hole parameters. We demonstrate that the known population of BBHs have spins that are both small, with μ ≈ 0, and very narrowly distributed, with σ2 ≤ 0.07 at 95% credibility. We then explore what these ensemble properties imply about the spins of individual BBH mergers, reanalyzing existing GW events with a population-informed prior on their effective spin. Under this analysis, the BBH GW170729, which previously excluded ${\chi }_{\mathrm{eff}}=0$ , is now consistent with zero effective spin at ∼10% credibility. More broadly, we find that uninformative spin priors generally yield overestimates for the effective spin magnitudes of compact binary mergers.
- Publication:
-
The Astrophysical Journal
- Pub Date:
- June 2020
- DOI:
- 10.3847/1538-4357/ab80c0
- arXiv:
- arXiv:2001.06051
- Bibcode:
- 2020ApJ...895..128M
- Keywords:
-
- Gravitational waves;
- LIGO;
- Black holes;
- Compact objects;
- Bayesian statistics;
- 678;
- 920;
- 162;
- 288;
- 1900;
- Astrophysics - High Energy Astrophysical Phenomena
- E-Print:
- 11 pages, 5 figures