GW231123's masses and high spins are consistent with primordial black holes that accreted mass and angular momentum in the early universe within the standard PBH framework.
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Are merging black holes born from stellar collapse or previous mergers?
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abstract
Advanced LIGO detectors at Hanford and Livingston made two confirmed and one marginal detection of binary black holes during their first observing run. The first event, GW150914, was from the merger of two black holes much heavier that those whose masses have been estimated so far, indicating a formation scenario that might differ from "ordinary" stellar evolution. One possibility is that these heavy black holes resulted from a previous merger. When the progenitors of a black hole binary merger result from previous mergers, they should (on average) merge later, be more massive, and have spin magnitudes clustered around a dimensionless spin ~0.7. Here we ask the following question: can gravitational-wave observations determine whether merging black holes were born from the collapse of massive stars ("first generation"), rather than being the end product of earlier mergers ("second generation")? We construct simple, observationally motivated populations of black hole binaries, and we use Bayesian model selection to show that measurements of the masses, luminosity distance (or redshift), and "effective spin" of black hole binaries can indeed distinguish between these different formation scenarios.
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Maximum-likelihood-based posterior predictive checks detect model misspecification better than event-level versions for uncertain spin tilts, but current detector sensitivity limits their power; the Gaussian Component Spins model underpredicts high spin magnitudes and overpredicts anti-aligned tilts
GWTC-4 data show a transition to nearly all hierarchical mergers above 46 solar masses, with the hierarchical rate peaking at 15.7 solar masses, indicating mass-dependent substructure in black hole spins.
LGWA could observe more than one third of known binary black hole events, detect ~90 mergers per year, and measure chirp mass better than third-generation detectors for massive systems.
Simulations with a new tidal model in COMPAS predict that merging binary black holes from isolated evolution are strongly biased to low effective spins, with one third below 0.05 and only 3% above 0.5, but the high-spin fraction rises to 15% at higher redshifts.
GWTC-5.0 analysis finds evidence for structure beyond a non-skewed Gaussian bulk in χ_eff, with suggestive mass-dependent excess of positive over negative spins outside the bulk at 13:1 odds in one mass bin.
Using HBI on GWTC-4 data the authors compute lensed SGWBs for ABHs and PBHs and conclude that LIGO and ET can distinguish the two formation channels in specific frequency ranges, with ET offering broader coverage.
GWTC-2.1 adds eight new high-significance compact binary coalescence events to the prior catalog, extending the observed black hole mass range and including candidates inside the pair-instability mass gap.
citing papers explorer
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Modern tidal interaction models for rapid binary population synthesis: II. Binary black hole formation, mergers, and spins
Simulations with a new tidal model in COMPAS predict that merging binary black holes from isolated evolution are strongly biased to low effective spins, with one third below 0.05 and only 3% above 0.5, but the high-spin fraction rises to 15% at higher redshifts.
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Evidence for additional structure in the effective spin distribution hints at multiple formation pathways in GWTC-5.0
GWTC-5.0 analysis finds evidence for structure beyond a non-skewed Gaussian bulk in χ_eff, with suggestive mass-dependent excess of positive over negative spins outside the bulk at 13:1 odds in one mass bin.
- A new group of low-spin $50-70M_\odot$ Black Holes and the high pair-instability mass cutoff
- Recoil kicks from binary black hole mergers in GWTC catalogs: implications for retention and hierarchical mergers