Three-body exchanges with primordial black holes

Abstract

The abundance of massive primordial black holes has historically been constrained by dynamical probes. Since these objects can participate in hard few-body scattering processes, they can readily transfer energy to stellar systems and, in particular, disrupt wide binaries. However, disruption is not the only possible outcome of such few-body processes. Primordial black holes could also participate in exchange processes, in which one component of a binary system is ejected and replaced by the black hole itself. In this case, the remaining object in the binary would dynamically appear to have an invisible companion. We study the rate of exchange processes for primordial black holes as a component of dark matter and evaluate possible mechanisms for detecting such binaries. We find that many such binaries plausibly exist in the Solar neighborhood and show that this process can account for observed binary systems whose properties run counter to the predictions of isolated binary evolution. Published by the American Physical Society 2025