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Recently discovered black hole is part of a nearby disrupted star cluster, study finds

Recently discovered black hole is part of a nearby disrupted star cluster, study finds
Gaia DR3 extinction corrected color-magnitude diagram (CMD) showing the location of the Gaia BH3 companion (red cross) and ED-2 members (B23) as blue and empty circles. Credit: arXiv (2024). DOI: 10.48550/arxiv.2404.11604

European astronomers have investigated a recently detected black hole designated Gaia BH3. In their results, they found that the black hole is associated with a nearby disrupted star cluster known as ED-2. The finding is reported in a paper published April 17 on the preprint server arXiv.

At a distance of some 1,900 , Gaia BH3 is a black hole discovered in April 2024 in a wide binary system within the galactic halo. It has a mass of about 33 , which makes it the most massive black hole of stellar origin known in our galaxy. The black hole's visible companion is an old, very metal-poor giant star, about five times larger than the sun, with a mass of approximately 0.76 solar masses. The system has a period of 11.6 years.

ED-2 is a disrupted old star cluster, which is now a galactic halo stellar stream. It is a dynamically cold stream crossing the solar neighborhood. The mean metallicity of ED-2 stars is estimated to be at a level of −2.60.

A team of astronomers led by Eduardo Balbinot of the University of Groningen in the Netherlands has investigated chemical abundances of ED-2 member stars and orbital characteristics of the Gaia BH3 binary. The obtained results indicate that Gaia BH3 belongs to the ED-2 stellar stream.

"We find that the galactic orbit of the Gaia BH3 system and its metallicity are entirely consistent with being part of the ED-2 stream," the researchers wrote in the paper.

The study found that the orbit of the black hole Gaia BH3 around the galaxy is indistinguishable from that of ED-2 member stars. It also turned out that only 17% of ED-2 members are closer to the than Gaia BH3.

The mean metallicity of the giant star in Gaia BH3 was found to be −2.56, which is close to the mean metallicity of stars in ED-2. Moreover, chemical elemental abundances such as magnesium, europium and barium-to-iron ratios of ED-2 members are consistent with that of the black hole's companion.

Therefore, according to the authors of the paper, these findings confirm that Gaia BH3 is unambiguously associated with the ED-2 stream.

The collected data also allowed the astronomers to shed more light on the formation of Gaia BH3 and ED-2. The results suggest that the progenitor of Gaia BH3 formed more than 13 billion years ago, and that the parent system of ED-2 was a small cluster with a mass smaller than 42,000 solar masses.

"This implies that the black hole could have formed directly from the collapse of a massive very-metal-poor star, but that the alternative scenario of binary interactions inside the cluster environment also deserves to be explored," the researchers concluded.

More information: E. Balbinot et al, The 33 M⊙ black hole Gaia BH3 is part of the disrupted ED-2 star cluster, arXiv (2024). DOI: 10.48550/arxiv.2404.11604

Journal information: arXiv

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Citation: Recently discovered black hole is part of a nearby disrupted star cluster, study finds (2024, April 25) retrieved 28 May 2024 from
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