Yellow Supergaint Vs. Blue Straggler: Was J01020100-7122208 Really Ejected From Black Hole Or SMC? (Cosmology)

K. Hawkins and colleagues performed a detailed analysis of J01020100-7122208 with the goal of shedding light on its origin. They proposed that, instead of yellow super giant and red giant, it is probably an evolved blue straggler. Their study recently appeared in Arxiv.

In 2018, astronomers using telescopes in northern Chile have discovered a rare runaway star in the Small Magellanic Cloud. The star is designated J01020100-7122208. It’s speeding across its little galaxy at 300,000 miles per hour (500,000 km/hour). They claimed, this star 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. Thus, its origin and nature still challenges us.

Now, in order to unveil its nature, K. Hawkins and colleagues, analysed photometric, astrometric and high resolution spectroscopic observations to estimate the orbit, age, and 16 elemental abundances.

Their results showed that this star has a retrograde and highly-eccentric orbit, e=0.914. Correspondingly, it likely crossed the Galactic disk at 550pc from the Galactic centre. They also obtained a spectroscopic mass and age of 1.09 M and 4.51 Gyr respectively.

Moreover, they found that its chemical composition is similar to the abundance of other retrograde halo stars and that the star is enriched in europium, having [Eu/Fe] = 0.93 ± 0.24, and is more metal-poor than reported in the literature, with [Fe/H] = -1.30 ± 0.10.

From this information they concluded that J01020100-7122208 is likely not a star ejected from the central black of the Milky Way or from the Small Magellanic Cloud. Instead, they proposed 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.

Reference: D. Brito-Silva, P. Jofré, D. Bourbert, S. E. Koposov, J. L. Prieto, K. Hawkins, “J01020100-7122208: an accreted evolved blue straggler that wasn’t ejected from a supermassive black hole”, Arxiv, 2021.

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