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| Authors | C. Hopman, S.F. Portegies Zwart, T. Alexander | | Title | Ultraluminous X-Ray Sources as Intermediate-Mass Black Holes Fed by Tidally Captured Stars |
| Journal | Astrophysical Journal |
| Volume | 604 |
| Year | 2004 |
| Pages | L101-L104 |
| ISSN | 0004637X |
| Faculty | Faculty of Science |
| Institute/dept. | FNWI: Astronomical Institute Anton Pannekoek (IAP)
FNWI: Informatics Institute (II) |
| Keywords | - |
| Abstract | The nature of ultraluminous X-ray (ULX) sources 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<SUB>BH</SUB>>10<SUP>6</SUP> M<SUB>solar</SUB> massive black holes in galactic centers, where survival is unlikely). We find that the capture and circularization rate is ~5?10<SUP>-8</SUP> yr<SUP>-1</SUP>, 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 source-like luminosities for greater than 10<SUP>7</SUP> yr. In particular, we show that the ULX source in the young cluster MGG-11 in starburst 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 timescale shorter than the lifetime of the binary. This raises the possibility of a ULX source that outlives its host cluster, or even lights up only after the cluster has evaporated, in agreement with observations of hostless ULX sources. |
| Document type | Article |
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