Discovery of a nearby 1700 kms¯1 star ejected from the Milky Way by Sgr A

S5 Collaboration, Sergey E. Koposov*, Douglas Boubert, Ting S. Li, Denis Erkal, Gary S. Da Costa, Daniel B. Zucker, Alexander P. Ji, Kyler Kuehn, Geraint F. Lewis, Dougal MacKey, Jeffrey D. Simpson, Nora Shipp, Zhen Wan, Vasily Belokurov, Joss Bland-Hawthorn, Sarah L. Martell, Thomas Nordlander, Andrew B. Pace, Gayandhi M. de SilvaMei Yu Wang

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

27 Citations (Scopus)
8 Downloads (Pure)


We present the serendipitous discovery of the fastest main-sequence hyper-velocity star (HVS) by the Southern Stellar Stream Spectroscopic Survey (S5). The star S5-HVS1 is a ∼2.35MA-type star located at a distance of ∼9 kpc from the Sun and has a heliocentric radial velocity of 1017 ± 2.7 kms-1 without any signature of velocity variability. The current 3D velocity of the star in the Galactic frame is 1755 ± 50 kms-1. When integrated backwards in time, the orbit of the star points unambiguously to the Galactic Centre, implying that S5-HVS1 was kicked away from Sgr A+ with a velocity of ∼1800 kms-1, travelled for 4.8 Myr to its current location. This is so far the only HVS confidently associated with the Galactic Centre. S5-HVS1 is also the first hyper-velocity star to provide constraints on the geometry and kinematics of the Galaxy, such as the Solar motion Vy, = 246.1 ± 5.3 km s-1 or position R0 = 8.12 ± 0.23 kpc. The ejection trajectory and transit time of S5-HVS1 coincide with the orbital plane and age of the annular disc of young stars at the Galactic Centre, and thus may be linked to its formation. With the S5-HVS1 ejection velocity being almost twice the velocity of other hyper-velocity stars previously associated with the Galactic Centre, we question whether they have been generated by the same mechanism or whether the ejection velocity distribution has been constant over time.

Original languageEnglish
Pages (from-to)2465-2480
Number of pages16
JournalMonthly Notices of the Royal Astronomical Society
Issue number2
Publication statusPublished - 1 Jan 2020

Bibliographical note

This article has been accepted for publication in Monthly Notices of the Royal Astronomical Society, Volume 491, Issue 2, January 2020, Pages 2465–2480, Copyright 2019 The Author(s). Published by Oxford University Press on behalf of the Royal Astronomical Society. All rights reserved.


  • Galaxy: centre
  • Galaxy: fundamental parameters
  • Stars: kinematics and dynamics


Dive into the research topics of 'Discovery of a nearby 1700 kms¯<sup>1</sup> star ejected from the Milky Way by Sgr A'. Together they form a unique fingerprint.

Cite this