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Eddington capture sphere around luminous stars

Journal article
Authors Adam Stahl
Maciej Wielgus
Marek A Abramowicz
Wlodek Kluźniak
Wenfei Yu
Published in Astronomy and Astrophysics
Volume 546
Issue 10
Pages artikel nr A54
ISSN 0004-6361
Publication year 2012
Published at Department of Physics (GU)
Pages artikel nr A54
Language en
Links dx.doi.org/10.1051/0004-6361/201220...
www.aanda.org/index.php?option=com_...
Subject categories High energy astrophysics, Astronomy

Abstract

Test particles infalling from infinity onto a compact spherical star with a mildly super-Eddington luminosity at its surface are typically trapped on the “Eddington capture sphere” and do not reach the surface of the star. The presence of a sphere on which radiation pressure balances gravity for static particles was first discovered some twenty five years ago. Subsequently, it was shown to be a capture sphere for particles in radial motion, and more recently also for particles in non-radial motion, in which the Poynting-Robertson radiation drag efficiently removes the orbital angular momentum of the particles, reducing it to zero. Here we develop this idea further, showing that “levitation” on the Eddington sphere (above the stellar surface) is a state of stable equilibrium, and discuss its implications for Hoyle-Lyttleton accretion onto a luminous star. When the Eddington sphere is present, the cross-section of a compact star for actual accretion is typically less than the geometrical cross-section πR2, direct infall onto the stellar surface only being possible for relativistic particles, with the required minimum particle velocity at infinity typically about half the speed of light. We further show that particles on typical trajectories in the vicinity of the stellar surface will also be trapped on the Eddington capture sphere.

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