Counting black holes: The cosmic stellar remnant population and implications for LIGO

Abstract

We present an empirical approach for interpreting gravitational wave signals of binary black hole mergers under the assumption that the underlying black hole population is sourced by remnants of stellar evolution. Using the observed relationship between galaxy mass and stellar metallicity, we predict the black hole count as a function of galaxy stellar mass. We show, for example, that a galaxy like the Milky Way should host millions of ∼ 30 M black holes and dwarf satellite galaxies like Draco should host ∼ 100 such remnants, with weak dependence on the assumed IMF and stellar evolution model. Most low-mass black holes (∼ 10M ) typically reside within massive galaxies (M 10 11 M ) while massive black holes (∼ 50 M ) typically reside within dwarf galaxies (M 10 9 M ) today. If roughly 1% of black holes are involved in a binary black hole merger, then the reported merger rate densities from Advanced LIGO can be accommodated for a range of merger timescales, and the detection of mergers with > 50 M black holes should be expected within the next decade. Identifying the host galaxy population of the mergers provides a way to constrain both the binary neutron star or black hole formation efficiencies and the merger timescale distributions; these events would be primarily localized in dwarf galaxies if the merger timescale is short compared to the age of the universe and in massive galaxies otherwise. As more mergers are detected, the prospect of identifying the host galaxy population, either directly through the detection of electromagnetic counterparts of binary neutron star mergers or indirectly through the anisotropy of the events, will become a realistic possibility.

PopSyCLE: A New Population Synthesis Code for Compact Object Microlensing Events

“…This is comparable the findings of Elbert et al (2018), where they estimate there should be around 10 8 black holes with M > 10M in a galaxy with a stellar mass equal to that of the Milky Way (M * ,M W ≈ 6 × 10 10 M ). Note that the models of Elbert et al (2018) include metallicity and BH-BH mergers, which PopSyCLE currently does not include. The mass distribution of BHs is shown in Figure 7.1 and a discussion of the distribution is presented in §7.1.…”

Populations of Stellar-mass Black Holes from Binary Systems

“…Some studies used a simplified approach. E.g., Elbert et al (2018) encapsulated all the interactions in just two parameters. In this study we focused on a detailed consideration of binary interactions, however, we neglected any higher-order systems (e.g.…”

Direct Constraints on the Ultralight Boson Mass from Searches of Continuous Gravitational Waves

“…Considering a supernova (of type II) rate of 2-3 per century in the Milky way [39], using the Kroupa initial mass function [40] and assuming that progenitor stars with masses larger than about 30 M ⊙ collapse to black hole, the current expected galactic black hole formation rate is about two per thousand years. Roughly 90% of them is expected to have mass smaller than about 30 M ⊙ and about 1% mass above ∼ 50 M ⊙ [41]. At distances from us smaller than d = 1 kpc, the formation rate is ∼ 2 × 10 −5 per year [42], so we do not expect any black hole with age less or equal to 10 3 years, hence the exclusion region shown in Fig.…”