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 _ { \bullet } > 10 ^ { 6 } M _ { \odot } massive black holes in galactic centers , where survival is unlikely ) .
We find that the capture and circularization rate is \sim 5 \times 10 ^ { -8 } { yr } ^ { -1 } , 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 > 10 ^ { 7 } { 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 \gtrsim 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 .