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Recent research has not entirely dismissed the possibility of an intermediate-mass black hole existing within the star cluster Omega Centauri; however, if such a black hole were present, its mass would be significantly less than earlier estimates. According to the analysis submitted on August 1 to arXiv.org, the team determined no black hole exists that is larger than 6,000 solar masses.
Conversely, another team of researchers posited that seven stars in close proximity to Omega Centauri’s core are exhibiting notably rapid movements, indicating that they are likely orbiting a black hole with a mass ranging from 8,200 to 50,000 solar masses (SN: 7/10/24). The quest to identify these intermediate-mass black holes has been ongoing, as their existence could enhance understanding of the formation and evolution of black holes throughout cosmic history.
In their study, lead researcher Bañares-Hernández and colleagues assessed the dynamics of not only ordinary stars in the cluster but also focused on five millisecond pulsars. These pulsars rotate at extraordinarily high speeds—over a hundred times per second—and emit regular radio pulses with each rotation. If a pulsar is moving toward Earth, its signals are received in shorter intervals. This precise timing enables astronomers to measure the pulsar’s velocity and acceleration accurately, shedding light on how mass is distributed in Omega Centauri.
Simon Portegies Zwart, an astronomer at Leiden Observatory who was not involved in either research project, praised the methodology used in the study. “This approach is among the best because millisecond pulsars provide highly stable signals that clearly illustrate the dynamics at play,” he stated.
The researcher who led the contrasting study has chosen not to comment on the new findings until they undergo formal publication, yet maintains confidence in his initial assessment. Maximilian Häberle from the Max Planck Institute for Astronomy in Heidelberg stated, “We believe the swift movements of these stars in Omega Centauri suggest they are influenced by an intermediate-mass black hole.”
Opinions among astronomers not affiliated with either study are varied. Gerry Gilmore from the University of Cambridge expressed skepticism regarding evidence for an intermediate-mass black hole, remarking, “The recent study substantially improved upon previous efforts by considering the types of dim stellar populations that are empirically known to be prevalent in globular cluster centers, such as neutron stars and stellar-mass black holes.”
On the contrary, Daryl Haggard from McGill University in Montreal found the support for the existence of a middleweight black hole to be “significantly persuasive.” He stated, “It is exceedingly challenging to devise a model that satisfactorily positions those fast-moving stars centrally in Omega Centauri without the influence of an intermediate-mass black hole.”
How can this scientific debate be resolved? Portegies Zwart highlighted the need for decisive evidence, stating, “What we require is an orbital trace.” He expressed a degree of skepticism towards the hypothesis of an intermediate-mass black hole, noting that the detection of a star orbiting an invisible, massive object would serve as compelling evidence. Haggard echoed this sentiment, adding that signs of gas emissions from material falling into such a black hole would also provide validation of their presence.
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