The Implications of High Black Hole Spins for the Origin of Binary Black Hole Mergers

Abstract

The LIGO–Virgo collaboration has reported 50 black hole–black hole (BH–BH) mergers and 8 candidates recovered from digging deeper into the detector noise. The majority of these mergers have low effective spins pointing toward low BH spins and efficient angular momentum (AM) transport in massive stars as proposed by several models (e.g., the Tayler–Spruit dynamo). However, out of these 58 mergers, 7 are consistent with having high effective-spin parameter (χ eff > 0.3). Additionally, two events seem to have high effective spins sourced from the spin of the primary (more massive) BH. These particular observations could be used to discriminate between the isolated binary and dynamical formation channels. It might seem that high BH spins point to a dynamical origin if AM in stars is efficient and forms low-spinning BHs. In such a case dynamical formation is required to produce second and third generations of BH–BH mergers with typically high spinning BHs. Here we show, however, that isolated binary BH–BH formation naturally reproduces such highly spinning BHs. Our models start with efficient AM in massive stars that is needed to reproduce the majority of BH–BH mergers with low effective spins. Later, some of the binaries are subject to a tidal spin-up allowing the formation of a moderate fraction (∼10%) of BH–BH mergers with high effective spins (χ eff ≳ 0.4–0.5). In addition, isolated binary evolution can produce a small fraction of BH–BH mergers with almost maximally spinning primary BHs. Therefore, the formation scenario of these atypical BH–BH mergers remains to be found.

Apples and Oranges: Comparing Black Holes in X-Ray Binaries and Gravitational-wave Sources

“…If some fraction of BBH progenitors are similar to the observed HMXBs, we may expect a subpopulation of BBH systems with (a) nearly aligned spins, typical of isolated binary evolution (Kalogera 2000;Fragos et al 2010;Rodriguez et al 2016;Stevenson et al 2017;Gerosa et al 2018), and (b) at least one rapidly spinning component, which will tend to be the primary BH, because the more massive component in a BBH is usually the first-born BH. This is in contrast to commonly considered evolutionary scenarios that produce a spinning second-born BH through tidal locking in the BH-He star binary phase (Kushnir et al 2016;Qin et al 2018;Zaldarriaga et al 2018;Bavera et al 2020;Mandel & Fragos 2020;Olejak & Belczynski 2021).…”

GWTC-3: Compact Binary Coalescences Observed by LIGO and Virgo During the Second Part of the Third Observing Run

“…Predictions for BH spin magnitudes vary, depending upon the formation channel and assumptions about stellar evolution such as stellar winds or the efficiency of stellar tides [179,216,291,[309][310][311]. If angular momentum transport is efficient in stars, then BHs formed from stellar collapse may be born with low ( 0.1) spins [312,313]; for binaries formed via isolated binary evolution, this may mean that the first-born BH is expected to have a low spin, although the second-born BH may have a larger spin due to tides spinning up its progenitor [314][315][316]. The situation may be different if progenitor stars have significant rotation rates, such as for close binary star systems, where tidal locking can lead to chemically homogeneous evolution [317][318][319].…”

Listening to the Universe with Next Generation Ground-Based Gravitational-Wave Detectors

“…GW catalogs compiled by other groups [19][20][21][22][23] have largely confirmed the population of coalescing compact bina-These discoveries have already made a massive impact on our understanding of different tenets of astrophysics, fundamental physics, and cosmology. They have allowed a first glimpse into the dynamics of strongly curved spacetimes and the validity of general relativity (GR) in unexplored regimes of the theory [29][30][31][32][33][34], raised deeper questions on the formation mechanisms and evolutionary scenarios of compact objects [16,18,[35][36][37][38][39][40][41][42][43][44][45][46], provided a new tool for measuring cosmic distances that will help in precision cosmology [47,48] and in mapping the large scale structure of the Universe [49][50][51][52], and brought to bear a novel approach to determine the structure and properties of NSs to help in the exploration of the dense matter equation of state which governs the dynamics of NS cores [53][54][55][56][57][58][59][60][61][62]. The second part of the third observing run saw the discovery of two neutron star-black hole binaries, GW200105...…”