Escape, capture, and levitation of matter in Eddington outbursts

TL;DR

This paper explores how intense radiation from luminous stars can eject, capture, or levitate matter, revealing conditions for plasma escape and equilibrium in relativistic gravity.

Contribution

It provides a detailed analysis of particle dynamics around highly luminous stars considering general relativity and radiation effects, identifying the Eddington capture sphere.

Findings

Particles outside the escape sphere are ejected by radiation pressure.

Particles inside the escape sphere are captured and levitated at the Eddington sphere.

Radiation drag causes captured particles to settle at the Eddington sphere in equilibrium.

Abstract

Context: An impulsive increase in luminosity by one half or more of the Eddington value will lead to ejection of all optically thin plasma from Keplerian orbits around the radiating star, if gravity is Newtonian and the Poynting-Robertson drag is neglected. Radiation drag may bring some particles down to the stellar surface. On the other hand, general relativistic calculations show that gravity may be balanced by a sufficiently intense radiation field at a certain distance from the star. Aims: We investigate the motion of test particles around highly luminous stars to determine conditions under which plasma may be ejected from the system. Results: In Einstein's gravity, if the outburst is close to the Eddington luminosity, all test particles orbiting outside an "escape sphere" will be ejected from the system, while all others will be captured from their orbits onto the surface of another sphere, which is well above the stellar surface, and may even be outside the escape sphere, depending on the value of luminosity. Radiation drag will bring all the captured particles to rest on this "Eddington capture sphere," where they will remain suspended in an equilibrium state as long as the local flux of radiation does not change and remains at the effective Eddington value.