Spin orientations of merging black holes formed from the evolution of stellar binaries

Abstract

We study the expected spin misalignments of merging binary black holes formed in isolation by combining state-of-the-art population-synthesis models with efficient post-Newtonian evolutions, thus tracking sources from stellar formation to gravitational-wave detection. We present extensive predictions of the properties of sources detectable by both current and future interferometers. We account for the fact that detectors are more sensitive to spinning black-hole binaries with suitable spin orientations and find that this significantly impacts the population of sources detectable by LIGO, while this is not the case for third-generation detectors. We find that three formation pathways, differentiated by the order of core collapse and common-envelope phases, dominate the observed population, and that their relative importance critically depends on the recoils imparted to black holes at birth. Our models suggest that measurements of the "effective-spin" parameter χ eff will allow for powerful constraints. For instance, we find that the role of spin magnitudes and spin directions in χ eff can be largely disentangled, and that the symmetry of the effective-spin distribution is a robust indicator of the binary's formation history. Our predictions for individual spin directions and their precessional morphologies confirm and extend early toy models, while exploring substantially more realistic and broader sets of initial conditions. Our main conclusion is that specific subpopulations of black-hole binaries will exhibit distinctive precessional dynamics: these classes include (but are not limited to) sources where stellar tidal interactions act on sufficiently short timescales, and massive binaries produced in pulsational pair-instability supernovae. Measurements of black-hole spin orientations have enormous potential to constrain specific evolutionary processes in the lives of massive binary stars.

Escape speed of stellar clusters from multiple-generation black-hole mergers in the upper mass gap

“…[69] for nonspinning BHs (Refs. [62,70,71] showed that spins have a marginal effect on p det unless strong alignment is present, which is not our case). The probability p det corresponds to the (unnormalized) detection rate, allowing us to estimate detector selection effects on the GW events resulting from our model.…”

Spins of black holes in coalescing compact binaries

“…Gravitational-wave astronomy offered new possibilities of direct measurement of BH spins in coalescing binary BHs. The current LIGO/Virgo results [16] suggest a fairly narrow effective BH spin distribution around zero χ eff ∼ 0, which can be used to understand the origin of coalescing binary BH with masses 10-60 M [73,74].…”

Gravitational waves from the quasicircular inspiral of compact binaries in Einstein-aether theory

“…Combining high-and low-frequency GW detections of the same source can also help identify the astrophysical channel responsible of BBH formations. Different scenarios in fact result in different masses, mass ratios, spins and eccentricity distributions of the detected sources [12][13][14][15][16][17]. Because of the GW circularization, BBHs may have small eccentricity in the LIGO/Virgo band, regardless of their formation channels.…”