Soliton Random Walk and the Cluster-Stripping Problem in Ultralight Dark Matter

TL;DR

This paper demonstrates that ultralight bosonic dark matter forms a soliton core that undergoes a random walk, which can gravitationally disrupt nearby star clusters, with implications for their longevity depending on halo stripping and tidal effects.

Contribution

It reveals the soliton's random walk behavior and its impact on star cluster stability, highlighting the importance of halo stripping and tidal forces in ultralight dark matter models.

Findings

Soliton undergoes a confined random walk within the halo.

Star clusters can be disrupted within ~1 Gyr due to soliton agitation.

Halo stripping and tidal effects influence star cluster survival times.

Abstract

Simulations of ultralight, $\sim 10^{-22}\,\rm eV$, bosonic dark matter exhibit rich wave-like structure, including a soliton core within a surrounding halo that continuously self-interferes on the de Broglie scale. We show here that as an inherent consequence, the soliton undergoes a confined random walk at the base of the halo potential. This is significant for the fate of the ancient central star cluster in Eridanus II, as the agitated soliton gravitationally shakes the star cluster in and out of the soliton on a time scale of $\sim 100\,\rm Myr$, so complete tidal disruption of the star cluster can occur within $\sim 1\,\rm Gyr$. This destructive effect can be mitigated by tidal stripping of the halo of Eridanus II, thereby reducing the agitation, depending on its orbit around the Milky Way. Our simulations show the Milky Way tide affects the halo much more than the soliton, so the star cluster in Eridanus II can survive for over $5\,\rm Gyr$ within the soliton if it formed after significant halo stripping.