Radiative Rayleigh-Taylor instabilities

TL;DR

This paper presents a linear stability analysis of interfaces between stratified media with radiation flux, deriving exact conditions for instabilities in different astrophysical regimes, including optically thin and thick cases.

Contribution

It develops a general analytical framework for radiative Rayleigh-Taylor instabilities and provides exact stability criteria in limiting regimes, extending classical results.

Findings

In optically thin regimes, radiation modifies effective gravity, leading to instability if gravity dominates.

In optically thick regimes, radiation acts as a modified equation of state, altering classical stability conditions.

Derived generalized Rayleigh-Taylor stability criterion incorporating radiation effects.

Abstract

We perform analytic linear stability analyses of an interface separating two stratified media threaded by a radiation flux, a configuration relevant in several astrophysical contexts. We develop a general framework for analyzing such systems, and obtain exact stability conditions in several limiting cases. In the optically thin, isothermal regime, where the discontinuity is chemical in nature (e.g.\ at the boundary of a radiation pressure-driven H \textsc{ii} region), radiation acts as part of an effective gravitational field, and instability arises if the effective gravity per unit volume toward the interface overcomes that away from it. In the optically thick "adiabatic" regime where the total (gas plus radiation) specific entropy of a Lagrangian fluid element is conserved,for example at the edge of radiation pressure-driven bubble around a young massive star, we show that radiation acts like a modified equation of state, and we derive a generalized version of the classical Rayleigh-Taylor stability condition.