It’s certainly not definitive.” (Baumgardt has posted his analyses online.)īaumgardt says that Vitral’s model does not account for mass segregation, in which heavier stars will gradually “sink” toward a cluster’s center, while lighter members move toward the edges. I have modeled M4 and don’t think an IMBH is needed. “There really might be globular clusters that could have IMBHs, like Omega Centauri or NGC 6388, but M4 looks pretty normal to me,” cautions Holger Baumgardt (University of Queensland, Australia), who was not involved in the study. Alternatively, there could be a central swarm of stellar remnants, such as black holes, neutron stars, or white dwarfs.īut not everyone thinks globular clusters like M4 are the best place to look for IMBHs. “Firstly, how an IMBH would affect the motions of the stars in the cluster, compared to a few stellar black holes, and also if there was no dark component present.” He and his team concluded that those motions might indicate the presence of a single IMBH of roughly 800 times the Sun’s mass. “We modeled a few different scenarios,” Vitral says. Hubble measured the motions of central stars, while Gaia provided the shape and mass of the cluster itself based on observations of 6,000 individual stars. (Non-subscribers may preview the issue at the link.)Įduardo Vitral (Space Telescope Science Institute) led a team that analyzed the proper motions of stars as they whizzed around the core of the globular cluster Messier 4 (M4). See Sky & Telescope ’s November 2022 issue for a survey of recent searches for intermediate-mass black holes. These spherical formations contain anywhere from thousands to millions of stars, packed so densely that we don’t really know what is at their centers. Globular clusters in particular are of interest for IMBH searches. And there are a few tentative detections in star clusters. X-ray observations have turned up a number of IMBH at the centers of dwarf galaxies. The LIGO and Virgo gravitational-wave instruments detected a black hole-binary collision of about 150 solar masses in 2020. Previously, observations have turned up hints of these objects. But there is a mysterious gap in between the two: We’ve never seen hard evidence for intermediate-mass black holes (IMBH). We’ve seen evidence for stellar-mass black holes, the result of collapsing stars, and we’ve observed supermassive black holes in the centers of galaxies. If the claim pans out - and that’s still up in the air - it would lend credence to the idea that at least some of these “missing links” are hiding inside dense star clusters. In a recent study using data from the Hubble Space Telescope and the Gaia spacecraft, astronomers report evidence that Messier 4, a globular cluster in the constellation Scorpius, could have a mid-size black hole lurking in its core.
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