SCYON Abstract

Received on March 16 2004

Ultraluminous X-ray sources as intermediate mass black holes fed by tidally captured stars

Authors	Clovis Hopman¹, Simon F. Portegies Zwart², Tal Alexander³
Affiliation	¹ Faculty of Physics, Weizmann Institute of Science, POB 26, Rehovot 76100, Israel; ² Astronomical Institute 'Anton Pannekoek', University of Amsterdam, Kruislaan 403, Netherlands; ³ Institute for Computer Science, University of Amsterdam, Kruislaan ⁴03, Netherlands
Accepted by	Astrophysical Journal
Contact	clovis.hopman@weizmann.ac.il
URL	http://xxx.lanl.gov/abs/astro-ph/0312597
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Abstract

The nature of ultraluminous X-ray sources (ULXs) is presently unknown. A possible explanation is that they are accreting intermediate mass black holes (IBHs) that are fed by Roche lobe overflow from a tidally captured stellar companion. We show that a star can circularize around an IBH without being destroyed by tidal heating (in contrast to the case of M > 10⁶ Msun massive black holes in galactic centers, where survival is unlikely). We find that the capture and circularization rate is ~ 5 x 10^-8/yr, almost independently of the cluster's relaxation time. We follow the luminosity evolution of the binary system during the main sequence Roche lobe overflow phase and show it can maintain ULX-like luminosities for > 10⁷ yr. In particular, we show that the ULX in the young cluster MGG-11 in star-burst galaxy M82, which possibly harbors an IBH, is well explained by this mechanism, and we predict that 10% of similar clusters with IBHs have a tidally captured circularized star. The cluster can evaporate on a time-scale shorter than the lifetime of the binary. This raises the possibility of a ULX that outlives its host cluster, or even lights up only after the cluster has evaporated, in agreement with observations of host-less ULXs.