Blue extreme disk-runaway stars with Gaia EDR3
Andreas Irrgang, Markus Dimpel, Ulrich Heber, Roberto Raddi

TL;DR
This study uses Gaia EDR3 data to analyze the origins and velocities of extreme disk-runaway stars, revealing most are not from the Galactic center but from the disk, with some exceeding classical ejection velocity limits.
Contribution
It provides the first detailed kinematic analysis of 30 extreme disk-runaway stars, challenging classical ejection scenarios and suggesting diverse origins including outer Galactic rings and satellite galaxies.
Findings
Most stars originate from the Galactic disk, not the center.
Several stars have ejection velocities exceeding classical predictions.
Some stars are unbound to the Milky Way, indicating extreme ejection events.
Abstract
Since the discovery of hypervelocity stars in 2005, it has been widely believed that only the disruption of a binary system by a supermassive black hole at the Galactic center (GC), that is, the so-called Hills mechanism, is capable of accelerating stars to beyond the Galactic escape velocity. In the meantime, however, driven by the Gaia space mission, there is mounting evidence that many of the most extreme high-velocity early-type stars at high Galactic latitudes do originate in the Galactic disk and not in the GC. Moreover, the ejection velocities of these extreme disk-runaway stars exceed the predicted limits of the classical scenarios for the production of runaway stars. Based on proper motions from the Gaia early data release 3 and on recent and new spectrophotometric distances, we studied the kinematics of 30 such extreme disk-runaway stars, allowing us to deduce their spatial…
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