Speaker
Description
Density spikes are steep enhancements in the dark matter (DM) distribution that arise from gravitational infall onto a central compact object. In the standard scenario where DM consists of particles, such spikes may form around a sub-dominant population of massive primordial black holes (PBHs), potentially leading to large enhancements of the DM density in their vicinity.
The situation can be qualitatively different if, instead, the bulk of the DM is also composed of PBHs, which are viable alternative candidates to particle DM and can constitute the entirety of it if, for example, they have masses around $M \sim 10^{17}-10^{22}\,\mathrm{g}$. In this scenario, lighter PBHs may avoid capture only if they develop enough angular momentum as a consequence of the torques exerted by both small-scale and large-scale fluctuations.
We investigate the mechanisms and initial conditions—such as the mass and initial separation from a central heavy PBH ($M \sim M_\odot$)—that enable lighter PBHs ($M \sim 10^{18}$–$10^{28}\mathrm{g}$) within such spikes to develop long-lived density enhancements. More specifically, we characterize the torque distribution and its evolution, and follow the resulting angular momentum dynamics using a combination of analytical approaches and numerical simulations.
