Pair instabilities in supernovae might prevent the formation of black holes with masses between ∼50 M⊙ and ∼130 M⊙. Multiple generations of black-hole mergers provide a possible way to populate ...this "mass gap" from below. However this requires an astrophysical environment with a sufficiently large escape speed to retain merger remnants, and prevent them from being ejected by gravitational-wave recoils. We show that, if the mass gap is indeed populated by multiple mergers, the observation of a single black-hole binary component in the mass gap implies that its progenitors grew in an environment with escape speed vesc≳50 km/s. This is larger than the escape speeds of most globular clusters, requiring denser and heavier environments such as nuclear star clusters or disks-assisted migration in galactic nuclei. A single detection in the upper mass gap would hint at the existence of a much larger population of first-generation events from the same environment, thus providing a tool to disentangle the contribution of different formation channels to the observed merger rate.
Two of the dominant channels to produce merging stellar-mass black-hole binaries are believed to be the isolated evolution of binary stars in the field and dynamical formation in star clusters. The ...first reported black-hole binary event from the third LIGO/Virgo observing run (GW190412) is unusual in that it has unequal masses, nonzero effective spin, and nonzero primary spin at 90% confidence interval. We show that this event should be exceedingly rare in the context of both the field and cluster formation scenarios. Interpreting GW190412 as a remnant of a previous black-hole merger provides a promising route to explain its features. If GW190412 indeed formed hierarchically, we show that the region of the parameter space that is best motivated from an astrophysical standpoint (low natal spins and light clusters) cannot accommodate the observation. We analyze public GW190412 LIGO/Virgo data with a Bayesian prior where the more massive black hole resulted from a previous merger and find that this interpretation is equally supported by the data. If the heavier component of GW190412 is indeed a merger remnant, then its spin magnitude is χ1=0.56−0.21+0.19, which is higher than the value previously reported by the LIGO/Virgo collaboration.
The inferred parameters of the binary black hole GW151226 are consistent with nonzero spin for the most massive black hole, misaligned from the binary's orbital angular momentum. If the black holes ...formed through isolated binary evolution from an initially aligned binary star, this misalignment would then arise from a natal kick imparted to the first-born black hole at its birth during stellar collapse. We use simple kinematic arguments to constrain the characteristic magnitude of this kick, and find that a natal kick v_{k}≳50 km/s must be imparted to the black hole at birth to produce misalignments consistent with GW151226. Such large natal kicks exceed those adopted by default in most of the current supernova and binary evolution models.
ABSTRACT
The progenitors of the high-mass black-hole mergers observed by LIGO and Virgo are potential LISA sources and promising candidates for multiband GW observations. In this letter, we consider ...the minimum signal-to-noise ratio these sources must have to be detected by LISA bearing in mind the long duration and complexity of the signals. Our revised threshold of ρthr ∼ 15 is higher than previous estimates, which significantly reduces the expected number of events. We also point out the importance of the detector performance at high frequencies and the duration of the LISA mission, which both influence the event rate substantially.
We present accurate fits for the remnant properties of generically precessing binary black holes, trained on large banks of numerical-relativity simulations. We use Gaussian process regression to ...interpolate the remnant mass, spin, and recoil velocity in the seven-dimensional parameter space of precessing black-hole binaries with mass ratios q≤2, and spin magnitudes χ_{1}, χ_{2}≤0.8. For precessing systems, our errors in estimating the remnant mass, spin magnitude, and kick magnitude are lower than those of existing fitting formulae by at least an order of magnitude (improvement is also reported in the extrapolated region at high mass ratios and spins). In addition, we also model the remnant spin and kick directions. Being trained directly on precessing simulations, our fits are free from ambiguities regarding the initial frequency at which precessing quantities are defined. We also construct a model for remnant properties of aligned-spin systems with mass ratios q≤8, and spin magnitudes χ_{1}, χ_{2}≤0.8. As a byproduct, we also provide error estimates for all fitted quantities, which can be consistently incorporated into current and future gravitational-wave parameter-estimation analyses. Our model(s) are made publicly available through a fast and easy-to-use Python module called surfinBH.
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 ?eff will allow for powerful constraints. For instance, we find that the role of spin magnitudes and spin directions in ?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.
Generic black hole binaries radiate gravitational waves anisotropically, imparting a recoil, or kick, velocity to the merger remnant. If a component of the kick along the line of sight is present, ...gravitational waves emitted during the final orbits and merger will be gradually Doppler shifted as the kick builds up. We develop a simple prescription to capture this effect in existing waveform models, showing that future gravitational wave experiments will be able to perform direct measurements, not only of the black hole kick velocity, but also of its accumulation profile. In particular, the eLISA space mission will measure supermassive black hole kick velocities as low as ∼500 km s^{-1}, which are expected to be a common outcome of black hole binary coalescence following galaxy mergers. Black hole kicks thus constitute a promising new observable in the growing field of gravitational wave astronomy.
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