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Discovery of a nearby 1700 km s-1 star ejected from the Milky Way by Sgr A*

Research output: Contribution to journalArticle

  • 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 Silva
  • Mei-Yu Wang
  • S5 collaboration

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Original languageEnglish
Pages (from-to)2465-2480
Number of pages16
JournalMonthly Notices of the Royal Astronomical Society
Issue number2
Early online date4 Nov 2019
Publication statusPublished - 1 Jan 2020


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 ∼2.35 M A-type star located at a distance of ∼9 kpc from the Sun and has a heliocentric radial velocity of 1017 ± 2.7 km s^{-1} without any signature of velocity variability. The current 3D velocity of the star in the Galactic frame is 1755 ± 50 km s^{-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 km s^{-1} and 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....

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