The best-known black holes are either extremely massive, such as the supermassive black holes that lie in the cores of large galaxies, or relatively light, with a mass less than 100 times that of the Sun. Intermediate-mass black holes (IMBHs) are rare, however, and are considered rare “missing links” in black hole evolution.
Now, an international team of astronomers has used more than 500 images from NASA’s Hubble Space Telescope — spanning two decades of observations — to look for evidence of an intermediate-mass black hole by following the motion of seven fast-moving stars. in the innermost region. of the Omega Centauri globular star cluster.
These stars provide compelling new evidence for the presence of gravitational pull from an intermediate-mass black hole pulling on them. Only a few other IMBH candidates have been found to date.
Omega Centauri consists of approximately 10 million stars that are gravitationally bound together. The cluster is about 10 times more massive than other large globular clusters – almost as massive as a small galaxy.
Among the many questions scientists want to answer: Are there any IMBHs, and if so, how common are they? Does a supermassive black hole grow from an IMBH? How are IMBHs themselves formed? Are dense star clusters their preferred home?
Astronomers have now created a huge catalog of the motions of these stars, measuring the velocities for 1.4 million stars collected from Hubble images of the cluster. Most of these observations were intended to calibrate Hubble’s instruments rather than for scientific use, but they proved to be an ideal database for the team’s research efforts.
“We discovered seven stars that shouldn’t be there,” explained Maximilian Häberle of the Max Planck Institute for Astronomy in Germany, who led the investigation. “They are moving so fast that they would escape the cluster and never return. The most likely explanation is that a very massive object is gravitationally pulling these stars and holding them close to the center. The only object that could life so massive is a black hole, with a mass at least 8,200 times that of our sun.”
Several studies have suggested the presence of an IMBH in Omega Centauri. However, other studies suggested that the mass could be contributed by a central cluster of stellar-mass black holes and had suggested that the lack of fast-moving stars above the necessary escape velocity made an IMBH less likely by comparison.
“This discovery is the most direct evidence yet of an IMBH in Omega Centauri,” added team leader Nadine Neumayer of the Max Planck Institute for Astronomy in Germany, who launched the study, along with Anil Seth of the University of Utah, Salt Lake. . The city. “This is exciting because there are only very few other known black holes of a similar mass. The Omega Centauri black hole may be the best example of an IMBH in our cosmic neighborhood.”
If confirmed, at a distance of 17,700 light-years, the candidate black hole lies closer to Earth than the 4.3-million-solar-mass black hole at the center of the Milky Way, located 26,000 light-years away.
Omega Centauri is visible from Earth with the naked eye and is one of the favorite celestial objects for stargazers living in the Southern Hemisphere. Located just above the plane of the Milky Way, the cluster appears almost as large as the full Moon when viewed from a dark rural area. It was first listed in Ptolemy’s catalog nearly 2,000 years ago as a single star. Edmond Halley reported it as a nebula in 1677. In the 1830s, the English astronomer John Herschel was the first to recognize it as a globular cluster.
The seminal paper led by Häberle et al. is published online today in the journal Nature.
The Hubble Space Telescope has operated for more than three decades and continues to make groundbreaking discoveries that shape our fundamental understanding of the universe. Hubble is an international collaboration project between NASA and ESA (European Space Agency). NASA’s Goddard Space Flight Center in Greenbelt, Maryland, manages the telescope and mission operations. Lockheed Martin Space, based in Denver, Colorado, also supports mission operations at Goddard. The Space Telescope Science Institute in Baltimore, Maryland, which is operated by the Association of Universities for Research in Astronomy, conducts Hubble science operations for NASA.