A Caltech Library Service

The Velocity Distribution of Hypervelocity Stars

Rossi, Elena M. and Kobayashi, Shiho and Sari, Re'em (2014) The Velocity Distribution of Hypervelocity Stars. Astrophysical Journal, 795 (2). Art. No. 125. ISSN 0004-637X.

PDF - Published Version
See Usage Policy.


Use this Persistent URL to link to this item:


We consider the process of stellar binaries tidally disrupted by a supermassive black hole (BH). For highly eccentric orbits, as one star is ejected from the three-body system, the companion remains bound to the BH. Hypervelocity stars (HVSs) observed in the Galactic halo and S-stars observed orbiting the central BH may originate from such mechanism. In this paper, we predict the velocity distribution of the ejected stars of a given mass, after they have traveled out of the Galactic potential. We use both analytical methods and Monte Carlo simulations. We find that each part of the velocity distribution encodes different information. At low velocities <800 km s^(−1), the Galactic potential universally shapes the observed distribution, which rises toward a peak, related to the Galactic escape velocity. Beyond the peak, the velocity distribution depends on binary mass and separation distributions. Finally, the finite star life introduces a break related to their mass. A qualitative comparison of our models with current observations shows the great potential of HVSs to constrain bulge and Galactic properties. Standard choices for parameter distributions predict velocities below and above ~800 km s^(−1) with equal probability, while none are observed beyond ~700 km s^(−1) and the current detections are more clustered at low velocities 300–400 km s^(−1). These features may indicate that the separation distribution of binaries that reach the tidal sphere is not flat in logarithmic space, as observed in more local massive binaries, but has more power toward larger separations, enhancing smaller velocities. In addition, the binary formation/evolution process or the injection mechanism might also induce a cut-off a_min ~ 10 R_☉ in the separation distribution.

Item Type:Article
Related URLs:
URLURL TypeDescription
Sari, Re'em0000-0002-1084-3656
Additional Information:© 2014 The American Astronomical Society. Received 2013 July 3; accepted 2014 July 11; published 2014 October 22.
Subject Keywords:binaries: general; Galaxy: center; Galaxy: halo; Galaxy: kinematics and dynamics; Galaxy: stellar content
Issue or Number:2
Record Number:CaltechAUTHORS:20141201-101644734
Persistent URL:
Official Citation:The Velocity Distribution of Hypervelocity Stars Elena M. Rossi et al. 2014 ApJ 795 125
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:52213
Deposited By: Jason Perez
Deposited On:01 Dec 2014 19:16
Last Modified:03 Mar 2020 13:01

Repository Staff Only: item control page