A preprint posted on arXiv (arXiv:2603.25795v1, not yet peer-reviewed) examines the LIGO-Virgo-KAGRA candidate event S251112cm, which shows signs of at least one compact object below one solar mass. Because stellar evolution cannot produce black holes this light, the authors explore whether the signal could instead come from primordial black holes (PBHs) formed in the first fractions of a second after the Big Bang.

The study’s methodology relies on analytic estimates of PBH binary merger rates, combined with existing observational upper limits on PBH abundance and the known sensitivity of current gravitational-wave detectors. No new observational data or large statistical sample is introduced; the calculation is based on a single candidate event and a range of theoretical assumptions about PBH mass distribution and clustering. The authors report that detection probability reaches unity (certainty within the model) for PBH masses around 0.5–1 solar mass under relaxed constraints, and remains roughly 0.5 in more conservative scenarios.

These numbers must be read with the paper’s own caveats: results are highly sensitive to astrophysical uncertainties in PBH abundance constraints, the precise merger-rate formula, and the exact sensitivity of the LVK network. The work therefore cannot be regarded as conclusive.

Looking beyond the preprint, this interpretation fits into a longer pattern of PBH research. Early papers such as Bird et al. (Phys. Rev. Lett. 116, 201301, 2016) first suggested PBHs could explain some LIGO stellar-mass mergers; later reviews (Carr, Kohri, Sendouda & Yokoyama, arXiv:2002.12778) mapped tight constraints across mass ranges. Sub-solar masses remain one of the less excluded windows because microlensing and cosmic-microwave-background limits weaken there. What the current preprint under-emphasizes is the cosmological payoff: a confirmed PBH population at this scale would directly probe the primordial power spectrum on small scales, constraining inflationary models in ways that large-scale CMB observations cannot.

It would also redraw the map of black-hole formation channels. Instead of only stellar collapse or dynamical assembly in dense clusters, a primordial channel would mean some black holes pre-date the first stars. This has obvious implications for dark-matter models—if even a modest fraction of dark matter is in 0.5–1 solar-mass PBHs, it would shift experimental priorities away from WIMPs and axions toward gravitational-wave and microlensing searches.

Still, important limitations remain. S251112cm is labeled a candidate, not a confirmed detection. The probability calculation depends on assumptions that future runs of LIGO, Virgo, and KAGRA may tighten or refute. Until multi-messenger confirmation or additional events appear, the PBH explanation stays plausible but speculative.