Motion in time-periodic backgrounds with applications to ultralight dark matter haloes at galactic centers

TL;DR

This paper investigates how stars move in time-periodic gravitational fields caused by ultralight dark matter haloes, revealing potential observable signatures such as orbital resonances and periodic modulations in emission lines.

Contribution

It provides a relativistic analysis of stellar motion in time-dependent backgrounds, highlighting observable effects of ultralight dark matter at galactic centers.

Findings

Orbital resonances can occur in time-periodic gravitational fields.

Spectroscopic emission lines show characteristic periodic modulations.

Stellar motions may carry imprints of ultralight dark matter.

Abstract

We consider motion in spherically symmetric but time-dependent backgrounds. This problem is of interest, for example, in the context of ultralight dark matter, where galactic haloes produce a time-dependent and periodic gravitational potential. We study the properties of motion of stars in such spacetimes, for different field strengths and frequency, and including dissipative effects. We show that orbital resonances may occur and that spectroscopic emission lines from stars in these geometries exhibit characteristic, periodic modulation patterns. In addition, we work out a fully relativistic and weak-field description of a special class of time-periodic geometries, that of scalar oscillatons. When applied to the galactic center, our results indicate that the motion of S2-like stars may carry distinguishable observational imprints of ultra-light dark matter.