The spatial and velocity distributions of hypervelocity stars

Abstract

Hypervelocity stars (HVSs) found in the Galactic halo are probably the dynamical products of interactions between (binary) stars and the massive black hole(s) (MBH) in the Galactic center (GC). It has been shown that the detected HVSs are spatially consistent with being located on two thin disks (Lu et al.), one of which has the same orientation as the clockwise-rotating stellar disk in the GC. Here we perform a large number of three-body experiments of the interactions between the MBH and binary stars bound to it, and find that the probability of ejecting HVSs is substantially enhanced by multiple encounters between the MBH and binary stars at distances substantially larger than the initial tidal breakup radii. Assuming that the HVS progenitors are originated from the two disks, the inclination distribution of the HVSs relative to the disk planes can be reproduced by either the mechanism of tidal breakup of binary stars or the mechanism of ejecting HVSs by a hypothetical binary black hole (BBH) in the GC. However, an isotropical origination of HVS progenitors is inconsistent with the observed inclination distribution. Assuming that the HVSs were ejected out by the tidal breakup mechanism, its velocity distribution can be reproduced if their progenitors diffuse onto low angular momentum orbits slowly and most of the progenitors were broken up at relatively large distances due to multiple encounters. Assuming that the HVSs were ejected out by a BBH within the allowed parameter space in the GC, our simulations produce relatively flatter velocity spectra compared to the observed ones; however, the BBH mechanism cannot be statistically ruled out, yet. Future surveys of HVSs and better statistics of their spatial and velocity distributions should enable to distinguish the ejection mechanisms of HVSs and shed new light on the dynamical environment of the MBH.(abridged)

19 pages, 16 figures

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Cited by in corpus (24)

• Progenitors of type Ia supernovae
• Stellar Dynamics and Stellar Phenomena Near A Massive Black Hole
• MMT Hypervelocity Star Survey III: A Complete Survey of Faint B-type Stars in the Northern Milky Way Halo
• The Great Escape: Discovery of a nearby 1700 km/s star ejected from the Milky Way by Sgr A*
• Mass-accreting white dwarfs and type Ia supernovae
• MMT Hypervelocity Star Survey. II. Five New Unbound Stars
• Predicted Space Motions for Hypervelocity and Runaway Stars: Proper Motions and Radial Velocities for the GAIA Era
• S-stars in the Galactic center and hypervelocity stars in the Galactic halo: two faces of the tidal breakup of stellar binaries by the central massive black hole?
• The Velocity Distribution of Hypervelocity Stars
• High velocity stars from the interaction of a globular cluster and a massive black hole binary
• Discovery of two new hypervelocity stars from the LAMOST spectroscopic surveys
• 591 high velocity stars in the Galactic halo selected from LAMOST DR7 and Gaia DR2
• Ejection and Capture Dynamics in Restricted Three-Body Encounters
• Metal-poor hypervelocity star candidates from the Sloan Digital Sky Survey
• New nearby hypervelocity stars and their spatial distribution from Gaia DR2
• On the Existence of Pulsars in the Vicinity of the Massive Black Hole in the Galactic Center
• Gravitational-wave merging events from the dynamics of stellar mass binary black holes around the massive black hole in a galactic nucleus
• A new Hyper-Runaway star discovered from LAMOST and GAIA: ejected almost in the galactic rotation direction
• Impact of the Galactic Disk and Large Magellanic Cloud on the Trajectories of Hypervelocity Stars Ejected from the Galactic Center
• The high velocity stars in the Local Stellar Halo from Gaia and LAMOST
• Constraints on the origins of hypervelocity stars: velocity distribution, mergers and star-formation history
• The Origin of HVS17, an Unbound Main Sequence B Star at 50 kpc
• Three New Late-type Hypervelocity Star Candidates from Gaia DR2 with Refined Selection Criteria
• A Recent Supermassive Black Hole Binary in the Galactic Center Unveiled by the Hypervelocity Stars