J01020100-7122208: an accreted evolved blue straggler that wasn't ejected from a supermassive black hole

TL;DR

This study characterizes star J01020100-7122208 as an accreted evolved blue straggler with a retrograde orbit, challenging previous ejection hypotheses from the Milky Way's black hole or the Small Magellanic Cloud.

Contribution

It provides a detailed analysis of the star's orbit, age, and chemical composition, revealing its likely origin as an accreted blue straggler rather than an ejected black hole star.

Findings

Star has a highly eccentric, retrograde orbit crossing near the Galactic center.

Chemical composition similar to retrograde halo stars, enriched in europium.

Likely an accreted blue straggler, not ejected from the Galactic center or SMC.

Abstract

J01020100-7122208 is a star whose origin and nature still challenges us. It was first believed to be a yellow super giant ejected from the Small Magellanic Cloud, but it was more recently claimed to be a red giant accelerated by the Milky Way's central black hole. In order to unveil its nature, we analysed photometric, astrometric and high resolution spectroscopic observations to estimate the orbit, age, and 16 elemental abundances. Our results show that this star has a retrograde and highly-eccentric orbit, $e=0.914_{-0.020}^{+0.016}$. Correspondingly, it likely crossed the Galactic disk at $550\;\mathrm{pc}$ from the Galactic centre. We obtained a spectroscopic mass and age of $1.09\pm0.10$ $M_\odot$ and $4.51\pm1.44$ Gyr respectively. Its chemical composition is similar to the abundance of other retrograde halo stars. We found that the star is enriched in europium, having [Eu/Fe] = 0.93 $\pm$ 0.24, and is more metal-poor than reported in the literature, with [Fe/H] = -1.30 $\pm$ 0.10. This information was used to conclude that J01020100-7122208 is likely not a star ejected from the central black of the Milky Way or from the Small Magellanic Cloud. Instead, we propose that it is simply a halo star which was likely accreted by the Milky Way in the distant past but its mass and age suggest it is probably an evolved blue straggler.