Lead author Daniel Hey explained, "Just like seismologists use earthquakes to study Earth's interior, we can use stellar oscillations to understand what's happening inside distant stars." These oscillations unveiled an unusual chemical profile indicating the star is alpha-rich, containing heavier elements typically seen in ancient stars, despite its relatively young age of about 5 billion years.
"Young, alpha-rich stars are quite rare and puzzling," Hey said. The study suggests the star may have merged with another or absorbed material when the black hole formed, explaining the unusual blend of youth and chemistry. Co-author Joel Ong added, "If this rotation is real, it can't be explained by the star's birth spin alone. The star must have been spun up through tidal interactions with its companion..."
Long-term measurements showed the star has a rotation period of 398 days, faster than expected for a red giant of its age, supporting the scenario of a dynamic evolutionary history. The researchers also studied Gaia BH3, another dormant black hole binary, where expected stellar oscillations were not detected, indicating a need to refine theoretical models for extremely metal-poor stars.
Both Gaia BH2 and BH3 have dormant black holes, showing no X-ray emissions, and their discovery was possible through precise tracking of stellar motions. Future TESS observations may confirm the merger hypothesis and clarify the origin of these systems.
Research Report:Asteroseismology of the Red Giant Companions to Gaia BH2 and BH3
Related Links
University of Hawaii at Manoa
Understanding Time and Space
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