Dancing with invisible partners: Three-body exchanges with primordial black holes

TL;DR

This paper investigates how primordial black holes can participate in three-body exchange interactions, potentially forming hidden binary systems that could explain certain observed stellar binaries inconsistent with isolated evolution.

Contribution

It introduces the concept of exchange processes involving primordial black holes, highlighting their role in forming invisible binary systems and challenging previous constraints based solely on disruption.

Findings

Many primordial black hole binaries likely exist nearby.

Exchange processes can produce binaries with properties unlike isolated evolution predictions.

This mechanism may explain certain anomalous observed binary systems.

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, can 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.