Publications associated with Theoretical Astrophysics & Plasma Physics

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

Monthly Notices of the Royal Astronomical Society Oxford University Press 491 (2019) 2465-2480

D Boubert, TS Li, D Erkal, GS Da Costa, DB Zucker, AP Ji, GF Lewis, K Kuehn, JD Simpson, D Mackey, N Shipp, V Belokurov, Z Wan, J Bland-Hawthorn, SL Martell, T Nordlander, D De Silva, M-Y Wang

<jats:title>Abstract</jats:title> <jats:p>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 3-D 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 disk 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.</jats:p>

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