Stability of Condensed Fuzzy Dark Matter Halos

TL;DR

This paper investigates the stability of ultralight axionic Fuzzy Dark Matter condensates, revealing their potential instability due to gravitational interactions with black holes and galaxy collisions, with implications for ultracompact dwarf galaxies.

Contribution

It provides a detailed analysis of the stability and decay timescales of FDM condensates under various astrophysical influences using the time-dependent variational method.

Findings

FDM condensates can become unstable via interactions with central black holes.

Galaxy collisions can also trigger instability in FDM condensates.

Decay of unstable condensates can last thousands of years.

Abstract

Stability properties of gravitationally bound condensates composed of ultralight axionic Fuzzy Dark Matter (FDM) are studied. Previous work has shown that astrophysical collisions could make self-gravitating condensates structurally unstable, making them prone to collapse and decay; in the context of FDM, we reexamine the relevant timescales using the time-dependent variational method. We show that FDM condensates can be made unstable through gravitational interactions with central black holes, for black hole masses in a phenomenologically relevant range. Instability could also be stimulated by galaxy collisions. The subsequent decay takes place over a period lasting as long as many thousands of years. We also discuss the possible relevance of FDM condensates to understanding the composition of Ultracompact Dwarf (UCD) Galaxies. Future observation of extremely massive black holes in the central regions of UCDs can constrain this interpretation.