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

Author:

Koposov Sergey E12ORCID,Boubert Douglas3ORCID,Li Ting S4567ORCID,Erkal Denis8ORCID,Da Costa Gary S9ORCID,Zucker Daniel B1011,Ji Alexander P4,Kuehn Kyler1213,Lewis Geraint F14ORCID,Mackey Dougal915,Simpson Jeffrey D16ORCID,Shipp Nora6717,Wan Zhen14ORCID,Belokurov Vasily2ORCID,Bland-Hawthorn Joss1415ORCID,Martell Sarah L1516ORCID,Nordlander Thomas915ORCID,Pace Andrew B18ORCID,De Silva Gayandhi M1315,Wang Mei-Yu1,

Affiliation:

1. McWilliams Center for Cosmology, Carnegie Mellon University, 5000 Forbes Ave, Pittsburgh, PA 15213, USA

2. Institute of Astronomy, University of Cambridge, Madingley Road, Cambridge CB3 0HA, UK

3. Magdalen College, University of Oxford, High Street, Oxford OX1 4AU, UK

4. Observatories of the Carnegie Institution for Science, 813 Santa Barbara Street, Pasadena, CA 91101, USA

5. Department of Astrophysical Sciences, Princeton University, Princeton, NJ 08544, USA

6. Fermi National Accelerator Laboratory, PO Box 500, Batavia, IL 60510, USA

7. Kavli Institute for Cosmological Physics, University of Chicago, Chicago, IL 60637, USA

8. Department of Physics, University of Surrey, Guildford GU2 7XH, UK

9. Research School of Astronomy and Astrophysics, Australian National University, Canberra, ACT 2611, Australia

10. Department of Physics, Astronomy, Macquarie University, Sydney, NSW 2109, Australia

11. Macquarie University Research Centre for Astronomy, Astrophysics, Astrophotonics, Sydney, NSW 2109, Australia

12. Lowell Observatory, 1400 W Mars Hill Rd, Flagstaff, AZ 86001, USA

13. Australian Astronomical Optics, Faculty of Science and Engineering, Macquarie University, Macquarie Park, NSW 2113, Australia

14. Sydney Institute for Astronomy, School of Physics, A28, The University of Sydney, NSW 2006, Australia

15. Centre of Excellence for All-Sky Astrophysics in Three Dimensions (ASTRO 3D), Australia

16. School of Physics, UNSW, Sydney, NSW 2052, Australia

17. Department of Astronomy, Astrophysics, University of Chicago, 5640 S Ellis Avenue, Chicago, IL 60637, USA

18. George P. and Cynthia Woods Mitchell Institute for Fundamental Physics and Astronomy, Department of Physics and Astronomy, Texas A&M University, College Station, TX 77843, USA

Abstract

ABSTRACT 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 $\mathrm{\, km\, s^{-1}}$ without any signature of velocity variability. The current 3D velocity of the star in the Galactic frame is 1755 ± 50 $\mathrm{\, km\, s^{-1}}$. 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 $\mathrm{\, km\, s^{-1}}$ 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 $\mathrm{\, km\, s^{-1}}$ 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.

Funder

European Space Agency

National Science Foundation

Heising-Simons foundation

National Aeronautics and Space Administration

Space Telescope Science Institute

Australian Research Council

Discovery Project

Publisher

Oxford University Press (OUP)

Subject

Space and Planetary Science,Astronomy and Astrophysics

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