2005/11/16 by Andrew King, A. R. King, R. Wijnands +1 · 2 citations
Physics and Astronomy · #Astronomy #Astrophysical Phenomena and Observations #Astrophysics #Astrophysics and Cosmic Phenomena #Galaxies: Formation, Evolution, Phenomena #Physics #astro-ph
paper · pdf · doi:10.1111/j.1745-3933.2005.00126.x
published as Mon.Not.Roy.Astron.Soc.Lett.366:L31-L34,2006 · Accepted for publication in MNRAS Letter
arxiv created 2005/11/16 · openalex publication_date 2006/01/06 · arxiv updated 2009/12/01 · openalex created_date 2025/10/10 · openalex updated_date 2026/08/05
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.