Implications for Primordial Black Hole Dark Matter from a Single Subsolar Mass Gravitational-wave Detection in LVK O1–O4

Abstract The detection of subsolar mass black holes is a milestone of modern astrophysics as it would open a window either onto new stellar physics or could potentially unveil the nature of dark matter as primordial black holes (PBHs). On 2025 November 12, the LIGO–Virgo–KAGRA (LVK) collaboration reported the compact binary merger candidate S251112cm, a system with no obvious electromagnetic counterpart, consistent with binary black hole merger with a chirp mass in the range 0.1–0.87 M ⊙ . The probability that at least one component has mass &lt;1 M ⊙ is &gt;99%. Inspired by this trigger, we tested if a population of PBHs formed at the quantum chromodynamics epoch with a broad mass function could account for a signal of this type. Our results, corresponding to a predicted event rate of 0.8 yr −1 as seen by LVK O3b, suggest that the observed merger rate of <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mn>0.2</mml:mn> <mml:msubsup> <mml:mrow> <mml:mn>3</mml:mn> </mml:mrow> <mml:mrow> <mml:mo>−</mml:mo> <mml:mn>0.218</mml:mn> </mml:mrow> <mml:mrow> <mml:mo>+</mml:mo> <mml:mn>0.86</mml:mn> </mml:mrow> </mml:msubsup> <mml:mspace width="0.25em"/> <mml:msup> <mml:mrow> <mml:mspace width="0.1em"/> <mml:mtext>yr</mml:mtext> <mml:mspace width="0.1em"/> </mml:mrow> <mml:mrow> <mml:mo>−</mml:mo> <mml:mn>1</mml:mn> </mml:mrow> </mml:msup> <mml:mspace width="0.25em"/> <mml:mo stretchy="false">(</mml:mo> <mml:mn>95</mml:mn> <mml:mo>%</mml:mo> <mml:mspace width="0.25em"/> <mml:mspace width="0.1em"/> <mml:mtext>C.L.</mml:mtext> <mml:mspace width="0.1em"/> <mml:mo stretchy="false">)</mml:mo> </mml:math> if the trigger is confirmed as an astrophysical event would be compatible with such a model. Our predicted detection rate is also in agreement with current LVK expectations for stellar-mass binaries, remaining consistent with a scenario in which a nonnegligible fraction of the 3–200 M ⊙ mergers observed by LVK originate from PBHs. If confirmed, this detection would place a lower limit to the PBH abundance f PBH &gt; 0.04 for our adopted model.