Stable, levitating, optically thin atmospheres of Eddington-luminosity neutron stars

TL;DR

This paper develops analytic models of stable, optically thin, levitating atmospheres around neutron stars at near-Eddington luminosities, showing they are stable and do not produce outflows.

Contribution

It introduces new analytic models of stable, levitating neutron star atmospheres supported by radiation pressure in the Schwarzschild metric.

Findings

Atmospheres are stable against convection and Rayleigh-Taylor instabilities.

Inner regions exhibit density and pressure inversions.

No gas outflows occur despite supercritical luminosity regions.

Abstract

In general relativity static gaseous atmospheres may be in hydrostatic balance in the absence of a supporting stellar surface, provided that the luminosity is close to the Eddington value. We construct analytic models of optically thin, spherically symmetric shells supported by the radiation pressure of a luminous central body in the Schwarzschild metric. Opacity is assumed to be dominated by Thomson scattering. The inner parts of the atmospheres, where the luminosity locally has supercritical values, are characterized by a density and pressure inversion. The atmospheres are convectively and Rayleigh-Taylor stable, and there is no outflow of gas.