Black holes at the heart of Milky Way’s largest star cluster reshaped in new research
by Sophie Jenkins
London, UK (SPX) Dec 13, 2024
For decades, scientists have debated the source of unusual star movements in Omega Centauri, the Milky Way’s largest star cluster. Recent research, incorporating new pulsar data, provides clarity, suggesting that a cluster of stellar-mass black holes, rather than a single intermediate-mass black hole (IMBH), is responsible.
Omega Centauri, home to nearly ten million stars, is located in the Centaurus constellation. Astronomers observed unexpectedly high velocities of stars near its center, sparking speculation about whether these were influenced by a massive IMBH-potentially 100,000 times the Sun’s mass-or numerous smaller stellar-mass black holes.
Intermediate-mass black holes are of particular interest because they might bridge the gap between stellar-mass black holes, which form from collapsing stars, and supermassive black holes, found at galaxy centers and weighing millions to billions of solar masses. Detecting an IMBH could provide insights into the formation of these cosmic giants.
New research led by the University of Surrey introduces pulsar acceleration data into the equation, refining previous models. Pulsars, dense remnants of massive stars, act as natural clocks due to their precise spin rates. By measuring changes in their spin rates, scientists can directly assess gravitational field strength, offering a new way to probe Omega Centauri’s core.
By combining pulsar acceleration measurements with stellar velocity data, researchers concluded that the gravitational forces at Omega Centauri’s center are more consistent with a cluster of stellar-mass black holes than a massive IMBH. However, a smaller IMBH-less than 6,000 solar masses-could still coexist with the black hole cluster.
Professor Justin Read of the University of Surrey noted, “The hunt for elusive intermediate-mass black holes continues. There could still be one at the centre of Omega Centauri, but our work suggests that it must be less than about six thousand times the mass of the Sun and live alongside a cluster of stellar mass black holes. There is, however, every chance of us finding one soon.”
Lead author Andre’s Ban~ares Herna’ndez from the Instituto de Astrofisica de Canarias added, “By studying Omega Centauri-a remnant of a dwarf galaxy-we have been able to refine our methods and take a step forward in understanding whether such black holes exist and what role they might play in the evolution of star clusters and galaxies. This work helps resolve a two-decade-long debate and opens new doors for future exploration.”
The study also sheds light on pulsar formation, a topic of growing interest due to recent discoveries of numerous pulsars. Researchers highlight that Omega Centauri provides an ideal environment to study these compact stars.
The findings, published in the paper *New constraints on the central mass contents of Omega Centauri from combined stellar kinematics and pulsar timing* (DOI: http://dx.doi.org/10.1051/0004-6361/202451763), mark a significant step forward in understanding the dynamic and enigmatic heart of Omega Centauri.
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