The Porous Atmosphere of eta Carinae

We analyze the wind generated by the great 20 yr-long super-Eddington outburst of eta Carinae. We show that by using the classical stellar atmosphere and wind theory, it is impossible to construct a consistent wind model in which a sufficiently small amount of mass, like the one observed, is shed. One expects the super-Eddington luminosity to drive a thick wind with a mass-loss rate substantially higher than the observed one. The easiest way to resolve the inconsistency is if we alleviate the implicit notion that atmospheres are homogeneous. An inhomogeneous, or "porous," atmosphere allows more radiation to escape while exerting a smaller average force. Consequently, such an atmosphere yields a considerably lower mass-loss rate for the same total luminosity. Moreover, all the applications of the Eddington luminosity as a strict luminosity limit should be revised or at least reanalyzed carefully.