Collapse versus Disruption: The Fate of Compact Stellar Systems in Ultralight Dark Matter Halos

TL;DR

This paper investigates how ultralight dark matter influences the evolution of compact stellar systems, revealing a complex interplay between internal relaxation and external heating that affects their stability and potential for disruption.

Contribution

The study introduces a numerical simulation framework to analyze the evolution of compact stellar systems in ULDM halos, highlighting the roles of relaxation and heating, and proposes an evolutionary phase diagram.

Findings

Relaxation-driven core collapse can keep systems bound and dense.

ULDM heating can dominate and disrupt more extended systems.

Identifies systems resembling ultra-faint dwarfs near disruption threshold.

Abstract

Interference of the ultralight dark matter (ULDM) field generates time-varying gravitational potential fluctuations, which stochastically heat stellar systems embedded in ULDM halos. Small-sized stellar systems are therefore often used to set stringent constraints on ULDM. However, the evolution of systems with sizes well below the ULDM de Broglie wavelength remains poorly explored. Using numerical simulations, we show that the evolution of compact stellar systems in ULDM halos is governed by the interplay between internal stellar relaxation and ULDM-induced heating. We find the following main results. First, in sufficiently compact systems, relaxation-driven core collapse dominates, allowing the system to remain bound and dense, while ULDM-induced stripping of outer stars further accelerates the collapse. Second, in more extended systems, ULDM heating dominates and ultimately disrupts the system. Near the disruption threshold, we identify systems resembling ultra-faint dwarfs like Segue 1. Third, we further introduce a dimensionless parameter to quantify the relative importance of heating and relaxation and finally lead to an evolutionary phase diagram. Our results reveal the rich and nontrivial dynamics of compact stellar systems in ULDM halos, indicating that precise system modeling is essential for robust ULDM constraints.