Eddington luminosity (sometimes also called the Eddington limit) is the largest luminosity that can pass through a layer of gas in hydrostatic equilibrium, supposing spherical symmetry. If the luminosity of a star exceeds the Eddington luminosity of a layer on the stellar surface, the gas layer is ejected from the star. This limit is obtained by equating the radiation pressure with gravitational forces. Since both forces decrease as inverse square laws, once equality is obtained this alters the hydrodynamics flow everywhere. // In General Physics In general physics, luminosity (more properly called luminance) is the density of luminous intensity in a given direction. ... A gas is one of the four main phases of matter (after solid and liquid, and followed by plasma), that subsequently appear as a solid material is subjected to increasingly higher temperatures. ... Hydrostatic equilibrium occurs when compression due to gravity is balanced by outward pressure. ... The Pleiades star cluster A star is a massive body of plasma in outer space that is currently producing or has produced energy through nuclear fusion. ...

The exact value of Eddington luminosity depends on the chemical composition of the gas layer and the spectral energy distribution of the emission. Gas with cosmological abundances of hydrogen and helium is much more transparent than gas with solar abundance ratios. Atomic line transitions can greatly increase the effects of radiation pressure, and line driven winds exist in some bright stars. The chemical composition of a substance refers to the elements of which the substance is composed. ...

Gamma ray bursts, Novae and supernovae are examples of systems exceeding their Eddington luminosity by a large factor for very short times. In those cases, the result is a radical change in physical structure (namely, the ejection of a fraction of the star's mass). Optical afterglow of gamma ray burst GRB-990123 (the bright dot within the white square and in the enlarged cutout) on 23 January 1999. ... This article needs to be cleaned up to conform to a higher standard of quality. ... Remnant of Keplers Supernova, SN 1604. ...

Some X-ray binaries and Active galactic nuclei are able to maintain luminosities close to the Eddington limit for very long times. X-ray binaries are a class of binary stars that are very luminous in X-rays. ... An active galaxy is a galaxy where a significant fraction of the energy output is not emitted by the normal components of a galaxy: stars, dust and interstellar gas. ...

The Eddington limit is not a true limit, and it is believed that photon-bubble instabilities (which remove the strict spherical symmetry) allow nature to have radiating flows with much higher luminosities. Super-Eddington accretion onto stellar-mass black holes is one possible model for Ultra Luminous Xray sources (ULX's).

If the Thomson scattering cross-section is used and the gas is assumed to be purely made of ionized hydrogen, the Eddington Luminosity is given by Thomson scattering is the scattering of electromagnetic radiation by a charged particle. ...

where M is the mass of the central object, m_p is the mass of a proton and σ_T is the Thomson cross-section.

References

• Juhan Frank, Andrew King, Derek Raine (2002). Accretion Power in Astrophysics, Third Edition, Cambridge University Press. ISBN 0521629578.