On the Origin of Hyper-Velocity Stars Near Sagittarius A*

Greenyer, George and Coulton, Antonio and Smith, Josh and Jaques, Rhys and Wright, Nathan and Wright, Keenan and Sobral, David (2020) On the Origin of Hyper-Velocity Stars Near Sagittarius A*. Notices of Lancaster Astrophysics (NLUAstro), 2. pp. 29-41.

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Abstract

We present our investigation into the origins of high- and hyper-velocity stars around the Milky Way by exploring Gaia data. We begin by establishing a working set of criteria for a star to even be considered as a potential hyper-velocity star, which we defined chronologically as: if the uncertainty in parallax is acceptably low; if the star has above average total velocity for its home set; and finally if the star has a velocity that is mostly radial we investigate it further. We also discuss the complications encountered trying to identify candidate stars. Finally, we perform a time-reversing procedure to trace our final set of stars back to where they may have originated. We found a large number of candidate stars in our initial broad range search, but by enforcing stricter constraints we found a final sample of 1,158 potential hyper-velocity stars. This set displayed zero stars passing close enough to Sagittarius A* to have been thrown out or boosted to their current velocities. However, by selecting hyper-velocity stars with little proper motion in right ascension and declination, we discovered five stars which may have passed close enough to Sagittarius A* to have had their orbits significantly altered. A detailed analysis of the trajectories of those stars was performed, resulting in one star that may have originated from a binary system that had a close encounter with Sagittarius A*. We propose a potential binary partner in some of the known stars orbiting Sagittarius A* with similar periapsis.