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Ultraluminous x-ray sources in external galaxies

King, A.R.; Davies, M.B.; Ward, M.J.; Fabbiano, G.; Elvis, M.


A.R. King

M.B. Davies

G. Fabbiano

M. Elvis


We investigate models for the class of ultraluminous nonnuclear X-ray sources (i.e., ultraluminous compact X-ray sources [ULXs]) seen in a number of galaxies and probably associated with star-forming regions. Models in which the X-ray emission is assumed to be isotropic run into several difficulties. In particular, the formation of sufficient numbers of the required ultramassive black hole X-ray binaries is problematic, and the likely transient behavior of the resulting systems is not in good accord with observation. The assumption of mild X-ray beaming suggests instead that ULXs may represent a short-lived 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 that is 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. These considerations still allow the possibility that individual ULXs may contain extremely massive black holes.


King, A., Davies, M., Ward, M., Fabbiano, G., & Elvis, M. (2001). Ultraluminous x-ray sources in external galaxies. Astrophysical Journal Letters, 552(2), L109-L112.

Journal Article Type Article
Publication Date 2001-05
Deposit Date May 20, 2008
Journal Astrophysical Journal Letters
Print ISSN 2041-8205
Electronic ISSN 2041-8213
Publisher American Astronomical Society
Peer Reviewed Peer Reviewed
Volume 552
Issue 2
Pages L109-L112
Keywords Accretion disks, Stars, Binaries, X-rays.