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Title: The faintest accretors
Authors: King, A. R.
Wijnands, R.
First Published: 1-Feb-2006
Publisher: Royal Astronomical Society (RAS)
Citation: Monthly Notices of the Royal Astronomical Society: LETTERS, 2006, 366 (1)
Abstract: Recent X-ray observations have detected a class of very faint X-ray transients in the Galaxy which probably reveal a previously unrecognized type of accretion on to neutron stars or black holes. We show that these systems cannot have descended from binaries with stellar-mass components of normal composition. Accretion of hydrogen-depleted matter on to stellar-mass black holes can account for individual systems, but requires that these transients should be observed to repeat within a few years, and does not explain why the class is distinctly faint. Two other explanations appear to be quite natural. One invokes accretion by neutron stars or stellar-mass black holes from companions that were already brown dwarfs or planets when the systems formed, i.e. which did not descend from low-mass stars. The other possibility is that these systems are the endpoints of primordial (zero-metallicity) binaries in which the primary was extremely massive, and collapsed to a black hole of mass ≳1000 M⊙. The (primordial) companion must by now have reached an extremely low mass (≲0.01 M⊙) and be transferring mass at a very low rate to the black hole. This picture avoids the main difficulty encountered by models invoking intermediate-mass black hole formation at non-primordial metallicities, and is a natural consequence of some current ideas about Population III star formation.
DOI Link: 10.1111/j.1745-3933.2005.00126.x
ISSN: 1745-3933
Version: Publisher Version
Status: Peer-reviewed
Type: Journal Article
Rights: This article has been accepted for publication in Monthly Notices of the Royal Astronomical Society ©: 2005 the authors. Published by Oxford University Press on behalf of the Royal Astronomical Society. All rights reserved. Deposited with reference to the publisher’s archiving policy available on the SHERPA/RoMEO website.
Appears in Collections:Published Articles, Dept. of Physics and Astronomy

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