Tidal capture of stars by intermediate-mass black holes

Recent X-ray observations and theoretical modelling have made it plausible that some ultraluminous X-ray sources (ULX) are powered by intermediate-mass black holes (IMBHs). N-body simulations have also shown that for certain initial conditions runaway merging of stars happens in dense star clusters, which could lead to the formation of IMBHs. In the present paper we have performed N-body simulations of young clusters such as MGG-11 of M82 in which IMBHs form through runaway merging. We took into account the effect of tidal energy dissipation of stars passing close to the IMBH to study the tidal capture and disruption of stars by IMBHs. In our simulations, IMBHs have a high chance of capturing stars through tidal energy dissipation within a few core relaxation times. For similar to 30 per cent of our runs a ULX is formed through tidal capture within 7-12 Myr, consistent with the age limits of MGG-11. Our results strengthen the case for some ULX being powered by IMBHs.