In a groundbreaking discovery, Chinese scientists have provided compelling evidence for the existence of intermediate-mass black holes (IMBHs), a missing link in our understanding of black hole evolution.
Researchers from the Chinese Academy of Sciences' National Astronomical Observatories (NAOC), working in collaboration with multiple institutions, identified a runaway star named J0731+3717. This star was ejected from the M15 globular cluster about 20 million years ago at an astonishing speed of nearly 550 kilometers per second.
IMBHs, which have masses between those of stellar-mass and supermassive black holes, are crucial to understanding how seed black holes evolve into the supermassive giants found at the centers of galaxies. Despite their significance, only a few controversial candidates for IMBHs have been identified, leaving their existence a debated topic in astrophysics.
The team's analysis of data from the European Space Agency's Gaia spacecraft and China's Large Sky Area Multi-Object Fiber Spectroscopic Telescope (LAMOST) revealed that J0731+3717 shares a near-identical chemical composition and age with M15, suggesting a dynamic past influenced by an IMBH.
Previously, observations hinted at the presence of an IMBH weighing between 1,700 to 3,200 solar masses at the center of M15. However, alternative explanations involving dense clusters of neutron stars remained plausible. The extreme velocity of J0731+3717 supports the presence of an IMBH by demonstrating that such high-speed ejection results from interactions with a massive black hole, a phenomenon known as the Hills mechanism.
Huang Yang, an associate professor at NAOC and co-lead of the study, explained that the tidal forces of an IMBH would rip a binary star apart, capturing one star while ejecting the other at high speed. This discovery paves the way for further research, with Zhang Huawei from Peking University's School of Physics expressing optimism about finding more such stars with ongoing and future data from Gaia and LAMOST.
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Chinese scientists find proof of intermediate-mass black holes
cgtn.com
