Misaligned streamers around a galactic centre black hole from a single cloud's infall

Abstract

We follow the near radial infall of a prolate cloud on to a 4×106M· supermassive black hole in the Galactic Centre using smoothed particle hydrodynamics. We show that a prolate cloud oriented perpendicular to its orbital plane naturally produces a spread in angular momenta in the gas which can translate into misaligned discs as is seen in the young stars orbiting Sagittarius A*. A turbulent or otherwise highly structured cloud is necessary to avoid cancelling too much angular momentum through shocks at closest approach. Our standard model of a 2×104M· gas cloud brought about the formation of a disc within 0.3 pc from the black hole and a larger, misaligned streamer at 0.5 pc. A total of 1.5 × 104M· of gas formed these structures. Our exploration of the simulation parameter space showed that when star formation occurred, it resulted in top-heavy initial mass functions with stars on eccentric orbits with semi-major axes 0.02-0.3 pc and inclinations following the gas discs and streamers. We suggest that the single event of an infalling prolate cloud can explain the occurrence of multiple misaligned discs of young stars. © 2013 The Authors Published by Oxford University Press on behalf of the Royal Astronomical Society.