Ultraluminous X-ray Sources in External Galaxies

Andrew King(Department of Physics and Astronomy, University of Leicester, Leicester LE1 7RH U.K.)

[Invited Review Talk, 30 min.]

Abstract

I consider models for the class of ultraluminous non-nuclear X-ray sources (ULXs) seen in a number of galaxies and probably associated with star-forming regions. While some individual ULXs could involve massive ( $> 10^5{\rm M_{\odot}}$) black holes emitting isotropically, this is not a promising model for the class. The assumption of mild X-ray beaming suggests instead that ULXs may represent a shortlived but extremely common stage in the evolution of a wide class of X-ray binaries. The best candidate for this is the phase of thermal-timescale mass transfer inevitable in many intermediate and high-mass X-ray binaries. This in turn suggests a link with the Galactic microquasars. The short lifetimes of high-mass X-ray binaries would explain the association of ULXs with episodes of star formation.

CATEGORY: BLACK HOLE AND NEUTRON STAR BINARIES NORMAL GALAXIES