The galactic center S-stars and the hypervelocity stars in the galactic halo: two faces of the tidal breakup of stellar binaries by the central massive black hole?
ZHANG F., LU Y. and YU Q.
Abstract (from CDS):
In this paper, we investigate the link between the hypervelocity stars (HVSs) discovered in the Galactic halo and the Galactic center (GC) S-stars, under the hypothesis that they are both the products of the tidal breakup of the same population of stellar binaries by the central massive black hole (MBH). By adopting several hypothetical models for binaries to be injected into the vicinity of the MBH and doing numerical simulations, we realize the tidal breakup processes of the binaries and their follow-up dynamical evolution. We find that many statistical properties of the detected HVSs and GC S-stars could be reproduced under some binary injecting models, and their number ratio can be reproduced if the stellar initial mass function is top-heavy (e.g., with slope ∼ - 1.6). The total number of the captured companions is ∼50 that have masses in the range ∼3-7 M☉ and semimajor axes ≲ 4000 AU and survive to the present within their main-sequence lifetime. The innermost one is expected to have a semimajor axis ∼300-1500 AU and a pericenter distance ∼10-200 AU, with a significant probability of being closer to the MBH than S2. Future detection of such a close star would offer an important test to general relativity. The majority of the surviving ejected companions of the GC S-stars are expected to be located at Galactocentric distances ≲ 20 kpc, and have heliocentric radial velocities ∼ - 500-1500 km/s and proper motions up to ∼5-20 mas/yr. Future detection of these HVSs may provide evidence for the tidal breakup formation mechanism of the GC S-stars.
black hole physics - Galaxy: center - Galaxy: halo - Galaxy: kinematics and dynamics - Galaxy: structure