Simulations of the tidal interaction and mass transfer of a star in an eccentric orbit around an intermediate-mass black hole: the case of HLX-1

Abstract

The X-ray source HLX-1 near the spiral galaxy ESO 243-49 is currently the best intermediate-mass black hole candidate. It has a peak bolometric luminosity of $10^{42}$ erg s$^{-1}$, which implies a mass inflow rate of $\sim10^{-4}$ MSun yr$^{-1}$, but the origin of this mass is unknown. It has been proposed that there is a star on an eccentric orbit around the black hole which transfers mass at pericentre. To investigate the orbital evolution of this system, we perform stellar evolution simulations using mesa and SPH simulations of a stellar orbit around an intermediate-mass black hole using fi. We run and couple these simulations using the amuse framework. We find that mass is lost through both the first and second Lagrange points and that there is a delay of up to 10 days between the pericentre passage and the peak mass loss event. The orbital evolution timescales we find in our simulations are larger than what is predicted by analytical models, but these models fall within the errors of our results. Despite the fast orbital evolution, we are unable to reproduce the observed change in outburst period. We conclude that the change in the stellar orbit with the system parameters investigated here is unable to account for all observed features of HLX-1.