Kinematics of hypervelocity stars in the triaxial halo of the Milky Way

Abstract

Hypervelocity stars (HVSs) ejected by the massive black hole at the Galactic center have unique kinematic properties compared to other halo stars. Their trajectories will deviate from being exactly radial because of the asymmetry of the Milky Way potential produced by the flattened disk and the triaxial dark matter halo, causing a change of angular momentum that can be much larger than the initial small value at injection. We study the kinematics of HVSs and propose an estimator of dark halo triaxiality that is determined only by instantaneous position and velocity vectors of HVSs at large Galactocentric distances (r>~50kpc). We show that, in the case of a substantially triaxial halo, the distribution of deflection angles (the angle between the stellar position and velocity vector) for HVSs on bound orbits is spread uniformly over the range 10--180deg. Future astrometric and deep wide-field surveys should measure the positions and velocities of a significant number of HVSs, and provide useful constraints on the shape of the Galactic dark matter halo.

10 pages,including 9 figures

References in corpus (1)

• The Shape of the Gravitational Potential in Cold Dark Matter Halos

Cited by in corpus (6)

• Hypervelocity Stars: From the Galactic Center to the Halo
• Milky Way potentials in CDM and MOND. Is the Large Magellanic Cloud on a bound orbit?
• Interaction of massive black hole binaries with their stellar environment: III. Scattering of bound stars
• Hypervelocity Stars III. The Space Density and Ejection History of Main Sequence Stars from the Galactic Center
• Hypervelocity Stars from the Andromeda Galaxy
• The nature of hypervelocity stars as inferred from their galactic trajectories