Subsolar mass black holes from stellar collapse induced by primordial black holes

While no gravitational-wave detection of subsolar mass black holes has been confirmed to date, a number of candidate detections invite us to speculate on the origin of such black holes should a detection be confirmed. It is generally assumed that the observation of a black hole with subsolar mass $M_{\mathrm{o}\mathrm{b}\mathrm{s}}$ would provide strong evidence for primordial black holes (PBHs). The mass $M_{\mathrm{P}\mathrm{B}\mathrm{H}}$ of the PBH, however, does not necessarily have to be equal to $M_{\mathrm{o}\mathrm{b}\mathrm{s}}$, as it would in what we term a direct PBH scenario". Instead, a black hole of mass $M_{\rm obs}$ may form in a capture of a much smaller primordial black hole, $M_{\rm PBH} \ll M_{\rm obs}$, by a dwarf star of mass $M_* \simeq M_{\rm obs}$, followed by the total consumption of the star by the PBH. We provide some rough estimates and demonstrate that such an indirect PBH scenario" may also lead to significant populations of black holes with mass $M_{\mathrm{o}\mathrm{b}\mathrm{s}}$, especially in dwarf galaxies, and may be able to explain rare subsolar mass events.