Reversible-jump MCMC analysis of LIGO binary black hole mergers identifies three subpopulations with distinct properties and independent redshift evolution.
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Evidence of the pair instability gap from black hole masses
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abstract
Stellar theory predicts a forbidden range of black-hole masses between ${\sim}50$--$130\,M_\odot$ due to pair-instability supernovae, but evidence for such a gap in the mass distribution from gravitational-wave astronomy has proved elusive. Early hints of a cutoff in black-hole masses at ${\sim} 45\,M_\odot$ disappeared with the subsequent discovery of more massive binary black holes. Here, we report evidence of the pair-instability gap in LIGO--Virgo--KAGRA's fourth gravitational wave transient catalog (GWTC-4), with a lower boundary of $44_{-4}^{+5} M_\odot$ (90\% credibility). While the gap is not present in the distribution of \textit{primary} masses $m_1$ (the bigger of the two black holes in a binary system), it appears unambiguously in the distribution of \textit{secondary} masses $m_2$, where $m_2 \leq m_1$. The location of the gap lines up well with a previously identified transition in the binary black-hole spin distribution; binaries with primary components in the gap tend to spin more rapidly than those below the gap. We interpret these findings as evidence for a subpopulation of hierarchical mergers: binaries where the primary component is the product of a previous black-hole merger and thus populates the gap. Our measurement of the location of the pair-instability gap constrains the $S$-factor for $^{12}\rm{C}(\alpha,\gamma)^{16}\rm{O}$ at 300keV to $260_{-108}^{+190}$ keV barns.
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A new model emphasizing secondary mass features and pairing transitions improves spectral siren H0 constraints by ~30% using 142 GW events from GWTC-4.0.
Millicharged particles weaken pulsational pair-instability in massive stars, shifting the lower edge of the black hole mass gap upward and turning gravitational wave observations into a probe for particles with masses 35-200 keV and charges 10^{-10} to 10^{-9}.
Joint strong-lensing and population inference on resolved gravitational-wave events finds no lensed events and tightens constraints on the black-hole merger rate peak redshift and high-redshift tail.
Presents a grid of 113 fast-rotating, chemically-homogeneous massive star models at Z=0.001 reaching core collapse with high angular momentum for use as supernova and GRB progenitors.
Dynamical formation in globular clusters produces a robust second black-hole mass peak at ~70 solar masses from second-generation mergers when the first-generation spectrum is truncated by pair-instability supernovae.
Simulations show a 40-50 solar-mass black-hole cutoff is not guaranteed to be confidently recovered from GWTC-4-like catalogs, spurious detections are unlikely, and O4 data would reduce cutoff-mass uncertainty by at least 20 percent while yielding only a lower bound on the carbon-alpha reaction rate
Using a joint effective-spin and precession-spin model on 155 gravitational-wave events, the authors infer that the hierarchical (second-generation) merger fraction rises sharply above ~46 M_sun and peaks again near 15.7 M_sun.
GWTC-4.0 reveals low-spin black holes up to ~68.5 Msun, implying a higher pair-instability mass cutoff and a lower 12C(alpha,gamma)16O rate.
GWTC-5 chirp-mass peaks form a ~1.9-spaced ladder with a new ~19 M⊙ rung matching predicted 2G+3G mergers, unifying prior 1G+2G spin-transition groups under one hierarchical scenario.
Hierarchical Bayesian analysis of GWTC-5 binary black hole spins finds no evidence for superradiant axions and excludes masses 1.7e-14 to 3.3e-12 eV at 95% CL.
A non-parametric reconstruction of the GWTC-5 black-hole population finds a separate high-mass subpopulation (M1 ≳ 50 M☉) with positively aligned spins (χ_eff ≈ 0.4).
Waveform modeling uncertainties can distort features in the binary black hole mass distribution inferred from gravitational-wave data more than statistical uncertainties.
No evidence for core-collapse formed low-spin IMBHs in GWTC-4, with 90% upper limit on merger rate of 0.077 Gpc^{-3} yr^{-1}, low-spin BH mass truncation at 65 solar masses consistent with pair-instability gap lower edge, and high-spin IMBHs from hierarchical mergers.
Stellar models show that the 12C(alpha,gamma)16O rate uncertainty moves the black hole mass gap, constraining its S300 to 137.6-263.4 keV barn when matched to the observed gap from gravitational waves.
Eccentric BBH signals recovered with quasi-circular precessing models show biases in chirp mass and χ_p; Bayes factors favor eccentric aligned-spin models when both eccentricity and precession are present.
Black hole spin constraints for Cyg X-1 from XRISM Resolve data are strongly model-dependent, ranging from a*~0.99 with relxill to a*~0 with relxillCp or reflkerrD.
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Reversible-jump MCMC reveals binary black hole subpopulations with distinct redshift evolution
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Secondary-Mass Features improve Spectral-Siren $H_0$ Constraints
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The Black Hole Mass Gap as a New Probe of Millicharged Particles
Millicharged particles weaken pulsational pair-instability in massive stars, shifting the lower edge of the black hole mass gap upward and turning gravitational wave observations into a probe for particles with masses 35-200 keV and charges 10^{-10} to 10^{-9}.
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Joint population and strong-lensing inference for resolved gravitational-wave events probes the black-hole merger rate beyond the peak of star formation
Joint strong-lensing and population inference on resolved gravitational-wave events finds no lensed events and tightens constraints on the black-hole merger rate peak redshift and high-redshift tail.
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Second-Generation Mass Peak in the Gravitational-Wave Population as a Probe of Globular Clusters
Dynamical formation in globular clusters produces a robust second black-hole mass peak at ~70 solar masses from second-generation mergers when the first-generation spectrum is truncated by pair-instability supernovae.
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Measurement prospects for the pair-instability mass cutoff with gravitational waves
Simulations show a 40-50 solar-mass black-hole cutoff is not guaranteed to be confidently recovered from GWTC-4-like catalogs, spurious detections are unlikely, and O4 data would reduce cutoff-mass uncertainty by at least 20 percent while yielding only a lower bound on the carbon-alpha reaction rate
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Signatures of a subpopulation of hierarchical mergers in the GWTC-4 gravitational-wave dataset
Using a joint effective-spin and precession-spin model on 155 gravitational-wave events, the authors infer that the hierarchical (second-generation) merger fraction rises sharply above ~46 M_sun and peaks again near 15.7 M_sun.
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A new group of low-spin $50-70M_\odot$ Black Holes and the high pair-instability mass cutoff
GWTC-4.0 reveals low-spin black holes up to ~68.5 Msun, implying a higher pair-instability mass cutoff and a lower 12C(alpha,gamma)16O rate.
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The Chirp-Mass Ladder: A New Rung Emerges
GWTC-5 chirp-mass peaks form a ~1.9-spaced ladder with a new ~19 M⊙ rung matching predicted 2G+3G mergers, unifying prior 1G+2G spin-transition groups under one hierarchical scenario.
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No Evidence for Superradiant Axions in LIGO-Virgo-KAGRA GWTC-5 Binary Black Hole Spins
Hierarchical Bayesian analysis of GWTC-5 binary black hole spins finds no evidence for superradiant axions and excludes masses 1.7e-14 to 3.3e-12 eV at 95% CL.
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When the black holes align: a subpopulation of aligned massive binary black holes observed via gravitational waves
A non-parametric reconstruction of the GWTC-5 black-hole population finds a separate high-mass subpopulation (M1 ≳ 50 M☉) with positively aligned spins (χ_eff ≈ 0.4).
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Is the Binary Black Hole Population Inference from Gravitational-Wave Data Robust?
Waveform modeling uncertainties can distort features in the binary black hole mass distribution inferred from gravitational-wave data more than statistical uncertainties.
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How do the LIGO-Virgo-KAGRA's Heavy Black Holes Form? No evidence for core-collapse Intermediate-mass black holes in GWTC-4
No evidence for core-collapse formed low-spin IMBHs in GWTC-4, with 90% upper limit on merger rate of 0.077 Gpc^{-3} yr^{-1}, low-spin BH mass truncation at 65 solar masses consistent with pair-instability gap lower edge, and high-spin IMBHs from hierarchical mergers.
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Constraints on the $^{12}$C$(\alpha, \gamma)^{16}$O and $^{16}$O+$^{16}$O Reaction Rates from Binary Black Holes Detected via Gravitational Wave Signals
Stellar models show that the 12C(alpha,gamma)16O rate uncertainty moves the black hole mass gap, constraining its S300 to 137.6-263.4 keV barn when matched to the observed gap from gravitational waves.
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Biased parameter inference of eccentric, spin-precessing binary black holes
Eccentric BBH signals recovered with quasi-circular precessing models show biases in chirp mass and χ_p; Bayes factors favor eccentric aligned-spin models when both eccentricity and precession are present.
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Model dependence of XRISM black-hole spin constraints in Cyg X-1
Black hole spin constraints for Cyg X-1 from XRISM Resolve data are strongly model-dependent, ranging from a*~0.99 with relxill to a*~0 with relxillCp or reflkerrD.