Evolution of dark matter microhalos through stellar encounters

Abstract

In the cold dark matter scenario, the smallest dark matter halos may be earth mass or smaller. These microhalos would be the densest dark matter objects in the Universe, making their accurate characterization important for astrophysical dark matter detection efforts. Moreover, their properties are closely linked to the nature of dark matter and the physics of the early universe, making them valuable cosmological probes. Dark matter microhalos survive as subhalos within larger galactic halos, but due to their small size, they are susceptible to encounters with individual stars. We use a large number of $N$-body simulations to develop a framework that can predict the evolution of a microhalo's density profile due to stellar encounters. We find that there is a universal density profile for microhalos subjected to stellar encounters, and each encounter alters a microhalo's scale parameters in a way that is simply related to the energy the encounter injects. Our framework can rapidly and accurately characterize the impact of stellar encounters on whole ensembles of microhalos, making it a promising tool for understanding the populations of microhalos within galactic halos.