2020/11/10 by Chase Kimball, Colm Talbot, Christopher P L Berry +11 · 1 voice · 17 citations
Physics and Astronomy · #Pulsars and Gravitational Waves Research #Cosmology and Gravitation Theories #Black Holes and Theoretical Physics
paper · pdf · doi:10.3847/2041-8213/ac0aef
Abstract We study the population properties of merging binary black holes in the second LIGO–Virgo Gravitational-Wave Transient Catalog assuming they were all formed dynamically in gravitationally bound clusters. Using a phenomenological population model, we infer the mass and spin distribution of first-generation black holes, while self-consistently accounting for hierarchical mergers. Considering a range of cluster masses, we see compelling evidence for hierarchical mergers in clusters with escape velocities ≳100 km s −1 . For our most probable cluster mass, we find that the catalog contains at least one second-generation merger with 99% credibility. We find that the hierarchical model is preferred over an alternative model with no hierarchical mergers (Bayes factor <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mi mathvariant="italic"></mml:mi> <mml:mo>></mml:mo> <mml:mn>1400</mml:mn> </mml:math> ) and that GW190521 is favored to contain two second-generation black holes with odds <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mi mathvariant="italic"></mml:mi> <mml:mo>></mml:mo> <mml:mn>700</mml:mn> </mml:math> , and GW190519, GW190602, GW190620, and GW190706 are mixed-generation binaries with <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mi mathvariant="italic"></mml:mi> <mml:mo>></mml:mo> <mml:mn>10</mml:mn> </mml:math> . However, our results depend strongly on the cluster escape velocity, with more modest evidence for hierarchical mergers when the escape velocity is ≲100 km s −1 . Assuming that all binary black holes are formed dynamically in globular clusters with escape velocities on the order of tens of km s −1 , GW190519 and GW190521 are favored to include a second-generation black hole with odds <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mi mathvariant="italic"></mml:mi> <mml:mo>></mml:mo> <mml:mn>1</mml:mn> </mml:math> . In this case, we find that 99% of black holes from the inferred total population have masses that are less than 49 M ⊙ , and that this constraint is robust to our choice of prior on the maximum black hole mass.