Picky Partners: The Pairing of Component Masses in Binary Black Hole Mergers
Abstract
We examine the relationship between individual black hole (BH) masses in merging binary black hole (BBH) systems. Analyzing the 10 BBH detections from LIGO/Virgo's first two observing runs, we find that the masses of the component BHs comprising each binary are unlikely to be randomly drawn from the same underlying distribution. Instead, the two BHs of a given binary prefer to be of comparable mass. We show that it is ∼5 times more likely that the component BHs in a given binary are always equal (to within 5%) than that they are randomly paired. If we assume that the probability of a merger between two BHs scales with the mass ratio q as q^{β}, so that β = 0 corresponds to random pairings, we find β > 0 is favored at credibility 0.987. By modeling the mass distribution, we find that the median mass ratio is q_{50 %}= 0.91_{0.17}^{+0.05} at 90% credibility. While the pairing between BHs depends on their mass ratio, we find no evidence that it depends on the total mass of the system. We predict that 99% of BBHs detected by LIGO/Virgo will have mass ratios q > 0.5. We conclude that merging black holes do not form random pairings; instead they are selective about their partners, preferring to mate with black holes of a similar mass. The details of these selective pairings provide insight into the underlying formation channels of merging binaries.
 Publication:

The Astrophysical Journal
 Pub Date:
 March 2020
 DOI:
 10.3847/20418213/ab7247
 arXiv:
 arXiv:1905.12669
 Bibcode:
 2020ApJ...891L..27F
 Keywords:

 Astrophysics  High Energy Astrophysical Phenomena;
 General Relativity and Quantum Cosmology
 EPrint:
 version accepted by ApJL