Evolutionary roads leading to low effective spins, high black hole masses, and O1/O2 rates for LIGO/Virgo binary black holes

Abstract

All ten LIGO/Virgo binary black hole (BH-BH) coalescences reported following the O1/O2 runs have near-zero effective spins. There are only three potential explanations for this. If the BH spin magnitudes are large, then: (i) either both BH spin vectors must be nearly in the orbital plane or (ii) the spin angular momenta of the BHs must be oppositely directed and similar in magnitude. Then there is also the possibility that (iii) the BH spin magnitudes are small. We consider the third hypothesis within the framework of the classical isolated binary evolution scenario of the BH-BH merger formation. We test three models of angular momentum transport in massive stars: a mildly efficient transport by meridional currents (as employed in the Geneva code), an efficient transport by the Tayler-Spruit magnetic dynamo (as implemented in the MESA code), and a very-efficient transport (as proposed by Fuller et al.) to calculate natal BH spins. We allow for binary evolution to increase the BH spins through accretion and account for the potential spin-up of stars through tidal interactions. Additionally, we update the calculations of the stellar-origin BH masses, including revisions to the history of star formation and to the chemical evolution across cosmic time. We find that we can simultaneously match the observed BH-BH merger rate density and BH masses and BH-BH effective spins. Models with efficient angular momentum transport are favored. The updated stellar-mass weighted gas-phase metallicity evolution now used in our models appears to be key for obtaining an improved reproduction of the LIGO/Virgo merger rate estimate. Mass losses during the pair-instability pulsation supernova phase are likely to be overestimated if the merger GW170729 hosts a BH more massive than 50 M⊙. We also estimate rates of black hole-neutron star (BH-NS) mergers from recent LIGO/Virgo observations. If, in fact. angular momentum transport in massive stars is efficient, then any (electromagnetic or gravitational wave) observation of a rapidly spinning BH would indicate either a very effective tidal spin up of the progenitor star (homogeneous evolution, high-mass X-ray binary formation through case A mass transfer, or a spin- up of a Wolf-Rayet star in a close binary by a close companion), significant mass accretion by the hole, or a BH formation through the merger of two or more BHs (in a dense stellar cluster).

GW190412: Observation of a binary-black-hole coalescence with asymmetric masses

“…Predictions for the spins of BHs at birth are highly uncertain, and are dependent on the efficiency of angular momentum transport in their massive-star progenitors as well as prior binary interactions, e.g., [231]. Recent work modeling the core-envelope interaction in massive stars finds angular momentum transport to be highly efficient, leading to stellar cores with extremely slow rotation prior to collapse, hence BHs with low spins (χ ∼ 0.01, e.g., [232][233][234]). Though particular phases of mass transfer early in the evolution of the primary star can potentially lead to significant spin at birth [235], modeling of this evolutionary pathway finds that it does not lead to systems that can merge as BBHs [235,236].…”

“…Binary interactions following the formation of the first-born BH, such as mass transfer from the companion star to the BH, are also inefficient at spinning up BHs significantly [237][238][239][240][241]. On the other hand, the naked helium star precursor of the second-born BH in an isolated binary system can potentially be spun up through tidal interactions with the alreadyborn BH if the system is in a tight enough orbital configuration [234,[242][243][244][245][246]. Hence, there is a range of expectations for the spin magnitudes of both the primary and secondary components of BBHs formed in isolation.…”

Fingerprints of Binary Black Hole Formation Channels Encoded in the Mass and Spin of Merger Remnants

“…Determining BH natal spins represents an issue that is still largely debated in the stellar evolution community. Some recent work has proposed a relation between the spin amplitude and the mass of the stellar carbon-oxygen core (e.g., Belczynski et al 2020). According to this prescription, BHs with natal masses  M 40  have natal spins above 0.8, with a slight dependence on the progenitor metallicity, while the spin decreases at increasing the BH mass.…”

Two Wolf–Rayet stars at the heart of colliding-wind binary Apep

“…Zhekov et al 2014;Shenar et al 2019), with the strongest cases being longer-lived main-sequence massive stars exhibiting a WN appearance (Schnurr et al 2008) and HD 5980 (Koenigsberger et al 2014). If Apep does harbour a binary comprising two classical WR stars, this will have important consequences for understanding the proposed anisotropic wind model and potential gravitational wave event progenitor systems (Belczynski et al 2020).…”