There are approximately 10 million stars in Omega Centauri, the largest star cluster in the Milky Way, and it behaves anomalously. Some in the center move faster than those at the ends. Two equally attractive possible explanations have been contemplated: the cluster could host an intermediate mass black hole, known as the “missing link”, or several clustered stellar mass black holes. Now, a recent study by several scientists from different astronomy and physics centers claims to have found an answer to this debate. Observational evidence, obtained through a new approach, suggests that the largest star cluster in the Milky Way hosts a cluster of stellar-mass black holes.
Pulsars solve the riddle
Astronomers solved the puzzle using pulsars as reference points. These are neutron stars, remnants of conventional stars that rotate extremely quickly and emit pulses of electromagnetic radiation at very precise rates. Some scientists consider pulsars as useful as an atomic clock, and their applications even include the analysis of gravitational waves.
“By carefully measuring changes in the pulsars’ spin rate, astronomers can calculate how they are accelerating, directly probing the strength of the gravitational field at the center of Omega Centauri. By combining these new acceleration measurements with stellar velocities, researchers have managed to differentiate between an intermediate mass black hole and a cluster of black holes,” explains a researcher. release from the University of Surrey, in the United Kingdom.
An unexpected response
The discovery did not leave the researchers completely satisfied. The team sought to find the first intermediate mass black hole. So far, those who investigate gravitational anomalies have identified supermassive black holes, with billions of solar masses, or very small ones, with just tens of solar masses. No one knows for sure how colossal black holes originate in the centers of galaxies. Discovering and studying one of intermediate mass could solve this puzzle. Hence the nickname ‘the missing link of black holes’.
Although the center of Omega Centauri did not offer the answer that astronomers were looking for, the method of arriving at it has proven to be quite precise. Using nearby pulsars to measure the gravitational field and determine the size of a black hole is a formula that could be applied in other regions of space in the future.
“We have been able to refine our methods and take a step forward in understanding whether these black holes exist and what role they might play in the evolution of star clusters and galaxies. This work helps resolve a two-decade debate and opens new doors for future exploration,” said Andrés Bañares Hernández, co-author of the study.
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