Dynamical Formation of the Gw150914 Binary Black Hole

Abstract

We explore the possibility that GW150914, the binary black hole (BBH) merger recently detected by Advanced LIGO, was formed by gravitational interactions in the core of a dense star cluster. Using models of globular clusters (GCs) with detailed N-body dynamics and stellar evolution, we show that a typical cluster with a mass ofis optimal for forming GW150914-like BBHs that will merge in the local universe. We identify the most likely dynamical processes for forming GW150914 in such a cluster, and we show that the detection of GW150914 is consistent with the masses and merger rates expected for BBHs from GCs. Our results show that dynamical processes provide a significant and well-understood pathway for forming BBH mergers in the local universe. Understanding the contribution of dynamics to the BBH merger problem is a critical step in unlocking the full potential of gravitational-wave astronomy.

Distinguishing Between Formation Channels for Binary Black Holes With Lisa

“…As was done in Rodriguez et al (2016), we assume that the GC population of the local universe is comprised of ∼ 44% high-metallicity GCs (0.25Z ), and ∼ 56% low-metallicity GCs (0.05Z and 0.01Z ). We further assign to each GC a tidal radius based on its galactocentric distance, which we assume to be correlated to its stellar metallicity based on observations of the Milky Way and other galaxies (Harris 2010).…”

“…The integral of the GC mass function over that bin then determines the weight assigned to that model. In other words, GC models with larger masses (3 × 10 5 M to 6 × 10 5 M , corresponding to models with initial particle numbers of 1 × 10 6 and 2 × 10 6 ) contribute more binaries than clusters with smaller masses (see Rodriguez et al 2016, for details). Once we select this population of binaries from all clusters, we generate a five-dimensional Gaussian kernel density estimate (KDE) from the formation masses, separation, eccentricity and ejection times of the BBH population.…”

“…For this study, we adopt the fiducial models of Rodriguez et al (2016) which are based on the most recent stellar evolution prescriptions for galactic fields (Dominik et al 2013).…”

“…Our population of dynamically-formed binaries is taken from a collection of 48 GC models developed in Rodriguez et al (2016) with the Cluster Monte Carlo (CMC) code (Pattabiraman et al 2013, and references therein). CMC employs a statistical approach to stellar dynamics, first developed by Hénon (1975), which enables the modeling of star clusters with significantly greater number of particles than a direct N -body simulation, while still employing the necessary physics-single and binary stellar evolution with BSE, 3-and 4-body strong gravitational encounters (Fregeau & Rasio 2007), and dynamical three-body binary formation (Morscher et al 2013)-to fully characterize the dynamical BBH merger problem.…”

Black hole mass function from gravitational wave measurements

“…Another reason to expect high values of q is scattering processes, either involving the BBH and an additional single BH, or between two BBHs. Simulations have shown that in dense environments, binaries tend to exchange components, preferentially ejecting their smaller partners in favor of more massive companions [72][73][74].…”