Hubble finds evidence for rare black hole in Omega Centauri

Using more than 500 images taken by the NASA/ESA Hubble Space Telescope over two decades, an international team of astronomers has detected seven fast-moving stars in the innermost region of Omega Centauri, the largest and most luminous globular cluster in the entire sky. These stars provide compelling new evidence for the existence of an intermediate-mass black hole.

Medium Mass Black Hole The IMBH (Intermediate Massive Holes) have long been sought as a “missing link” in the evolution of black holes. Only a few IMBH candidates have been discovered so far. Most known black holes are Supermassive black hole They are either found at the centre of large galaxies or are relatively light objects with masses less than 100 times that of the Sun.

Black holes are some of the most extreme environments known to man, and serve as testing grounds for our understanding of the laws of physics and how the universe works. If they exist, how common are they? Supermassive black hole Do they grow from IMBHs? How do IMBHs themselves form? Are dense star clusters the preferred locations for IMBHs?

Omega Centauri is visible to the naked eye from Earth and is one of the favourite objects for stargazers in the Southern Hemisphere. The star cluster lies 17,000 light-years away and sits just above the plane of the Milky Way, but from a dark countryside it appears roughly the same size as the full moon.

The exact classification of Omega Centauri has evolved over time as research capabilities have improved. The star was first described as a single star in the Ptolemy catalogue about 2000 years ago. Edmond Halley reported the nebula in 1677, and British astronomer John Herschel first recognised it as a globular cluster in the 1830s.

Globular clusters, which typically consist of up to one million old stars held tightly together by gravity, are found in both the peripheral and central regions of many galaxies, including our own. Omega Centauri has several characteristics that set it apart from other globular clusters: it rotates faster than typical globular clusters and is very flat in shape. Additionally, Omega Centauri is about 10 times more massive than other large globular clusters and roughly the same mass as a small galaxy.

Omega Centauri is made up of roughly 10 million gravitationally bound stars, and an international team studied more than 500 Hubble Space Telescope images of the cluster to measure the velocities of 1.4 million stars and compile a vast catalogue of their motions.

Although most of these observations were intended to calibrate Hubble’s instruments rather than for scientific use, they proved to be an ideal database for the team’s research efforts. This extensive catalogue, the largest catalogue of star cluster motions to date, is scheduled to be made publicly available. Astrophysical Journal And this article is now Available To arXiv Preprint server.

“We found seven stars that shouldn’t be there,” explained Maximilian Höberle of the Max Planck Institute for Astronomy in Germany, who led the survey. “They are moving so fast that they should have fled the cluster and never come back.”

“The most likely explanation is that a very massive object is gravitationally tugging on these stars, pinning them near the center. The only object this massive is a black hole, which has a mass at least 8,200 times that of the Sun.”

Some studies suggest that an IMBH exists at Omega Centauri, but others suggest that its mass may be provided by a central cluster of stellar-mass black holes, making the existence of an IMBH unlikely since there are no stars moving fast enough to overcome the necessary escape velocity.

“This discovery is the most direct evidence to date for the presence of an intermediate-mass black hole in Omega Centauri,” added team leader Nadine Neumeyer of the Max Planck Institute for Astronomy, who initiated the study. “This is very intriguing because very few other black holes with a similar mass are known. The Omega Centauri black hole may be the best example of an intermediate-mass black hole in our cosmic neighborhood.”

If confirmed, the potential black hole would be 17,000 light-years from Earth, closer to Earth than the Sun’s 4.3-million-mass black hole at the center of the Milky Way, which is 26,000 light-years away, and would be the only known example of multiple stars intimately bound to a massive black hole outside the center of a galaxy.

The science team now wants to characterize the black hole, which is thought to be at least 8,200 times the mass of the Sun, but its exact mass and precise location are not fully understood. The team also plans to study the orbits of fast-moving stars, which requires further measurements of their radial speed.

The team has been given time to use the NASA/ESA/CSA James Webb Space Telescope to do just that, and also has pending proposals to use other observatories.

Omega Centauri also featured in the recent release of new data from ESA’s Gaia mission, which includes more than 500,000 stars.

“Thirty years later, the Hubble Space Telescope and its imaging instruments remain one of the best tools for high-precision astronomical measurements in stellar dense regions, areas where Hubble can provide additional sensitivity from ESA’s Gaia mission observations,” said team member Mattia Librato from the Italian National Institute for Astrophysics (INAF), who was part of the European Space Agency’s AURA at the time of the study.

“Our results demonstrate the high resolution and sensitivity of the Hubble Space Telescope and will provide new scientific insights and provide new impetus for the study of intermediate-mass black holes in globular clusters.”