This article has been reviewed according to Science X's editorial process and policies. Editors have highlighted the following attributes while ensuring the content's credibility: A new study suggests that the young stars orbiting the Milky Way's central black hole may have a surprisingly ordinary origin. But the black hole's influence may be what makes their origin look more exotic than it really is.
Along with shaping their orbits, it may also destroy their stellar companions. The paper outlining this work was published in Astronomy & Astrophysics on Aug. 11. A cluster of stars known as the S cluster sits very close to the Milky Way's central supermassive black hole, Sagittarius A* (Sgr A*), at a distance of some 0.04 parsecs (0.13 light-years).
The black hole has a mass around 4 million times that of the sun. These B-type stars are surprisingly young—a few million years old on average. But conventional star formation shouldn't be possible this close to a black hole, since the black hole's intense gravity should tear apart any gas cloud before it collapses to form stars.
Astronomers call this puzzling situation the "paradox of youth." There are two proposed ideas for how the young S stars could have formed. In situ formation proposes that the stars formed where we see them today. It involves a powerful Sgr A* outburst about 6 million years ago.
The resulting outflow could have compressed surrounding gas into a shell, which then fragmented to form stars. This theory is called gas-shell fragmentation. Ex situ formation suggests the stars formed farther away and later moved inward.
One possibility is that the stars formed farther out in a separate, well-known disk structure, then migrated inward over time, but this struggles to explain the S stars' high, nearly random orbital eccentricities and why B stars would migrate while O and Wolf–Rayet stars did not. Another possibility is the Hills mechanism, in which Sgr A* tears apart an incoming binary, capturing one star and flinging its companion as a high-velocity star. But the high-velocity stars found near the galactic center are much older than S stars, and this mechanism would leave behind almost no binary systems among the S cluster.
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