The nearest middle-aged black hole could be a crowd of lightweights

The study doesn’t completely rule out an intermediate-mass black hole, but if one is there, it’s much smaller than previously suggested. No black holes larger than 6,000 times the mass of the Sun exist in the star cluster, his team concludes in work submitted Aug. 1 to arXiv.org.

In contrast, the other research team said that seven stars near this cluster’s center are moving fast enough to orbit a black hole with masses between 8,200 and 50,000 solar masses.SN: 7/10/24). Astronomers have long sought these intermediate-mass black holes because, if the elusive objects really do exist, they could help explain the evolution of black holes.

In the new work, Baares-Hernndez and his colleagues studied the motions of not only ordinary stars in Omega Centauri, but also five of its millisecond pulsars. Rotating at more than a hundred times per second, a millisecond pulsar fires a radio pulse at us every time the star turns (SN: 22.7.22). If the pulsar is moving towards Earth, each pulse takes less time to reach us. Therefore, the precise timing of these pulses reveals the precise speed and acceleration of the pulsar toward or away from Earth, which helped astronomers determine how the mass is distributed throughout the star cluster.

It’s probably one of the best methods to use because millisecond pulsars are very stable and they give you a very clear signal of what’s going on, says Simon Portegies Zwart, an astronomer at the Leiden Observatory in the Netherlands, who was not part of or research team.

The astronomer who led that study declined to comment on the new work until it was accepted for publication, but he stands by his original conclusion. We think the best explanation for these fast-moving stars being so close to the center of Omega Centauri is that they are bound by an intermediate-mass black hole, says Maximilian Hberle of the Max Planck Institute for Astronomy in Heidelberg. Germany.

Astronomers not affiliated with either research team are divided in their verdict. I don’t think there is any strong evidence for an intermediate-mass black hole, says Gerry Gilmore, an astronomer at the University of Cambridge. In the new study, they did a much better job than anyone before, including types of [dim] The stellar populations we really know are very, very common in the centers of globular clusters: neutron stars and stellar-mass black holes.

On the other hand, astronomer Daryl Haggard of McGill University in Montreal calls the evidence for a medium-mass black hole quite compelling. It’s very, very, very difficult to come up with a model that puts those fast-moving stars at the center of Omega Centauri without them being driven by an intermediate-mass black hole.

How to resolve the dispute? Give me an orbit, says Portegies Zwart, who says he is a little skeptical about the existence of the intermediate-mass black hole. A star orbiting something invisible weighing thousands of solar masses would be strong evidence, he says. So would a glow from gas falling into a black hole, Haggard says.