Superradiance in stars: non-equilibrium approach to damping of fields in stellar media

Abstract

Superradiance in black holes is well-understood but a general treatment for superradiance in stars has until now been lacking. This is surprising given the ease with which we can observe isolated neutron stars and the array of signatures which would result from stellar superradiance. In this work, we present the first systematic pipeline for computing superradiance rates in rotating stars. Our method can be used with any Lagrangian describing the interaction between the superradiant field and the constituents of the star. Our scheme falls into two parts: firstly we show how field theory at finite density can be used to express the absorption of long wavelength modes into the star in terms of microphsyical scattering processes. This allows us to derive a damped equation of motion for the bosonic field. We then feed this into an effective theory for long wavelengths (the so-called worldline formalism) to describe the amplification of superradiant modes of arbitrary multipole moment for a rapidly rotating star. Our method places stellar superradiance on a firm theoretical footing and allows the calculation of the superradiance rate arising from any interaction between a bosonic field and stellar matter.

A generic formation mechanism of ultralight dark matter solar halos

“…Additionally, the process is effective when m is of the order of the black hole radius 1/(2GM ), and therefore, for fixed M , is active for larger boson masses (by a factor 2π/v dm ) than those for which DM capture starts to be effective, ξ foc ≃ 1. 31 Similar processes can occur in dense stellar objects like neutron stars, but require additional SM couplings beyond gravity and are not relevant for less dense objects like our Sun [142]. Finally, the particles produced by the Sun that lie in the low-velocity tail of the distribution can get captured into bound orbits around the Sun, giving rise to yet-another bound configuration, a solar basin [124,125,143].…”

Astrophysical Axion Bounds: The 2024 Edition

“…Superradiance requires dissipation which in rotating BHs is provided by their ergoregion,7 but does not exist in neutron stars. Recent works have proposed that enough dissipation may come from finite conductivity either in the stellar magnetosphere [419,420] or within the star itself [421,422], but one may wonder if the required conditions can be met in realistic pulsars. More work may be needed to substantiate this exciting possibility.…”

Boson star superradiance

“…Superradiance in rotating stars has recently been discussed in refs. [67][68][69][70][71]. Reviews about superradiance can be found in refs.…”