Astrophysical Bose-Einstein Condensates and Superradiance

TL;DR

This paper models slowly rotating astrophysical objects like dark matter halos as Bose-Einstein condensates using gravitational analogue models, analyzing their stability, fluctuation dynamics, and superradiant scattering effects.

Contribution

It introduces a relativistic Lagrangian-based approach to describe Bose-Einstein condensates in gravitational potentials and explores superradiance phenomena in this context.

Findings

Background equations are stable under small rotational perturbations.

Fluctuation dynamics follow a Klein-Gordon equation in a derived Eulerian metric.

Conditions for superradiant scattering are established and estimated.

Abstract

We investigate gravitational analogue models to describe slowly rotating objects (e.g., dark-matter halos, or boson stars) in terms of Bose-Einstein condensates, trapped in their own gravitational potentials. We begin with a modified Gross-Pitaevskii equation, and show that the resulting background equations of motion are stable, as long as the rotational component is treated as a small perturbation. The dynamics of the fluctuations of the velocity potential are effectively governed by the Klein-Gordon equation of a "Eulerian metric," where we derive the latter by the use of a relativistic Lagrangian extrapolation. Superradiant scattering on such objects is studied. We derive conditions for its occurence and estimate its strength. Our investigations might give an observational handle to phenomenologically constrain Bose-Einstein condensates.