Hubble finds evidence of rare black hole in Omega Centauri

An international team of astronomers has used more than 500 images from the NASA/ESA Hubble Space Telescope over two decades to find seven fast-moving stars in the interior of Omega Centauri, the largest and brightest globular cluster in the sky. These stars provide new evidence for the existence of an intermediate-mass black hole.

Intermediate-mass black holes (IMBHs) are the long-awaited „missing link” in black hole evolution. Only a few other IMBH candidates have been identified to date. Most known black holes are either supermassive, such as the supermassive black holes at the centers of large galaxies, or relatively light, with masses less than 100 times that of the Sun.

Black holes are among the most extreme environments known to humans, and are therefore a testing ground for our understanding of the laws of physics and how the universe works. If there are IMBHs, how common are they? Will a supermassive black hole grow from the IMPH? How do IMBHs form? Are dense star clusters their preferred home?

Omega Centauri is visible to the naked eye from Earth and is one of the favorite celestial objects of stargazers in the Southern Hemisphere. Although the cluster is 17,000 light-years away and lies just above the plane of the Milky Way, it appears as large as the full moon when viewed from the dark countryside.

The exact classification of Omega Centauri has evolved over time as our ability to study it has improved. It was first listed as a star in Ptolemy’s catalog 2000 years ago. Edmund Halley declared it a nebula in 1677, and the English astronomer John Herschel first recognized it as a globular cluster in the 1830s.

Globular clusters typically contain 1 million old stars tightly bound together by gravity and are found in the outskirts and central regions of many galaxies, including our own. Omega Centauri has several characteristics that distinguish it from other globular clusters: it rotates faster than a run-of-the-mill globular cluster, and its shape is much flatter. Also, Omega Centauri is about 10 times larger than other large globular clusters, almost as large as a small galaxy.

Omega Centauri contains about 10 million stars bound together by gravity. An international team has now compiled an enormous catalog of the motions of these stars, measuring velocities for 1.4 million stars by analyzing more than 500 Hubble images.

Most of these observations were intended to calibrate Hubble’s instruments rather than for scientific use, but they became an excellent database for the team’s research efforts. A comprehensive catalog, the largest catalog of motions for any constellation to date, is apparently available. It’s coming The Astrophysical Journal And the article is present Available On top of that arXiv Preprint server.

„We found seven stars that shouldn’t be there,” explained Maximilian Heberle of the Max Planck Institute for Astronomy in Germany, who led the investigation. „They move so fast that they escape the cluster and never come back.

„The most likely explanation is that a very large object is gravitationally pulling these stars closer to the center. The only object that could be this large is a black hole, which has a mass at least 8200 times that of our Sun.”

Several studies have suggested the presence of an IMBH in Omega Centauri. However, other studies have proposed that mass can be contributed by the central cluster of stellar-mass black holes, and suggested that the IMBH is relatively small because there are no stars moving faster than the required escape velocity.

„This discovery is the most direct evidence of an IMBH in Omega Centauri,” said Nadine Neumeyer, head of the team at the Max Planck Institute for Astronomy, which initiated the study. „This is exciting because there are only a few other black holes of similar mass. The black hole in Omega Centauri may be the best example of an IMBH in our universe.”

If confirmed, the candidate black hole at 17,000 light years away is closer to Earth than the 4.3 million solar mass black hole at the center of the Milky Way, 26,000 light years away. This is the only known case of multiple stars being closely bound to a supermassive black hole, other than the galactic center.

The science team now hopes to classify the black hole. It is believed to measure at least 8,200 solar masses, although its exact mass and its precise position are not fully known. The team also wants to study the orbits of fast-moving stars, which requires additional measurements of their respective line-of-sight velocities.

The team has been granted time with the NASA/ESA/CSA James Webb Space Telescope, and other plans to use other observatories are pending.

Omega Centauri is the latest feature in a new data release from ESA’s Gaia mission, which contains more than 500,000 stars.

„Even after 30 years, the Hubble Space Telescope, with its imaging instruments, is one of the best tools for high-precision astronomy in crowded interstellar fields, areas that can provide additional sensitivity from ESA’s Gaia mission observations,” shared team member Mattia Libralato. National Institute of Astrophysics (INAF) in Italy, and AURA before the European Space Agency during this study.

„Our results demonstrate Hubble’s high resolution and sensitivity, which give us exciting new scientific insights and will give new impetus to the topic of IMBHs in globular clusters.”