Hubble finds evidence for rare black hole in Omega Centauri (2024)
Science & Exploration
10/07/20241536 views13 likes
An international team of astronomers has used more than 500 images from the NASA/ESA Hubble Space Telescope spanning two decades to detect seven fast-moving stars in the innermost region of Omega Centauri, the largest and brightest globular cluster in the sky. These stars provide compelling new evidence for the presence of an intermediate-mass black hole.
Intermediate-mass black holes (IMBHs) are a long-sought ‘missing link’ in black hole evolution. Only a few other IMBH candidates have been found to date. Most known black holes are either extremely massive, like the supermassive black holes that lie at the cores of large galaxies, or relatively lightweight, with a mass less than 100 times that of the Sun. Black holes are one of the most extreme environments humans are aware of, and so they are a testing ground for the laws of physics and our understanding of how the Universe works. If IMBHs exist, how common are they? Does a supermassive black hole grow from an IMBH? How do IMBHs themselves form? Are dense star clusters their favoured home?
Omega Centauri is visible from Earth with the naked eye and is one of the favourite celestial objects for stargazers in the southern hemisphere. Although the cluster is 17 000 light-years away, lying just above the plane of the Milky Way, it appears almost as large as the full Moon when seen from a dark rural area. The exact classification of Omega Centauri has evolved through time, as our ability to study it has improved. It was first listed in Ptolemy's catalogue nearly 2000 years ago as a single star. Edmond Halley reported it as a nebula in 1677, and in the 1830s the English astronomer John Herschel was the first to recognise it as a globular cluster.
Globular clusters typically consist of up to one million old stars tightly bound together by gravity and are found both 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 highly flattened. Moreover, Omega Centauri is about 10 times as massive as other big globular clusters, almost as massive as a small galaxy.
Omega Centauri consists of roughly 10 million stars that are gravitationally bound. An international team has now created an enormous catalogue of the motions of these stars, measuring the velocities for 1.4 million stars by studying over 500 Hubble images of the cluster. Most of these observations were intended to calibrate Hubble’s instruments rather than for scientific use, but they turned out to be an ideal database for the team’s research efforts. The extensive catalogue, which is the largest catalogue of motions for any star cluster to date, will be made openly available (more information is availablehere).
“We discovered seven stars that should not be there,”explained Maximilian Häberle of the Max Planck Institute for Astronomy in Germany, who led this investigation.“They are moving so fast that they should escape the cluster and never come back. The most likely explanation is that a very massive object is gravitationally pulling on these stars and keeping them close to the centre. The only object that can be so massive is a black hole, with a mass at least 8200 times that of our Sun.”
Several studies have suggested the presence of an IMBH in Omega Centauri[1]. However, other studies proposed that the mass could be contributed by a central cluster of stellar-mass black holes, and had suggested the lack of fast-moving stars above the necessary escape velocity made an IMBH less likely in comparison.
“This discovery is the most direct evidence so far of an IMBH in Omega Centauri,”added team lead Nadine Neumayer, also of the Max Planck Institute for Astronomy, who initiated the study. “This is exciting because there are only very few other black holes known with a similar mass. The black hole in Omega Centauri may be the best example of an IMBH in our cosmic neighbourhood.”
If confirmed, at its distance of 17 000 light-years the candidate black hole resides closer to Earth than the 4.3 million solar mass black hole in the centre of the Milky Way, which is 26 000 light-years away. Besides the galactic centre, it would also be the only known case of a number of stars closely bound to a massive black hole.
The science team now hopes to characterise the black hole. While it is believed to measure at least 8200 solar masses, its exact mass and its precise position are not fully known. The team also intends to study the orbits of the fast-moving stars, which requires additional measurements of the respective line-of-sight velocities. The team has been granted time with the NASA/ESA/CSAJames Webb Space Telescopeto do just that, and also has other pending proposals to use other observatories.
Omega Centauri was also a recent feature of a new data release from ESA’s Gaia mission, whichcontained over 500 000 stars.“Even after 30 years, the Hubble Space Telescope with its imaging instruments is still one of the best tools for high-precision astrometry in crowded stellar fields,regions where Hubble can provide added sensitivity from ESA’s Gaia mission observations,”shared team member Mattia Libralato of the National Institute for Astrophysics in Italy (INAF), and previously of AURA for the European Space Agency during the time of this study.“Our results showcase Hubble’s high resolution and sensitivity that are giving us exciting new scientific insights and will give a new boost to the topic of IMBHs in globular clusters.”
Notes [1]In2008, the Hubble Space Telescope and the Gemini Observatory found that the explanation behind Omega Centauri's peculiarities may be a black hole hidden in its centre.
More information TheHubble Space Telescopeis a project of international cooperation between ESA and NASA. The HST observations featured in this release include those from program16790,13937, and16995(A. Simon).
An intermediate-mass black hole (IMBH) is a class of black hole with mass in the range of tens to tens thousand (102–105) solar masses: significantly higher than stellar black holes but lower than the tens thousand to hundreds trillion (105–1015) solar mass supermassive black holes.
https://en.wikipedia.org › wiki › Intermediate-mass_black_hole
in Omega Centauri. Seven fast-moving stars in the center of the cluster "that should not be there" indicate the presence of an 8,200-solar-mass black hole. Black holes come in three weight classes: stellar-mass black, intermediate-mass black, and supermassive.
Images obtained with the Hubble Space Telescope's Advanced Camera for Surveys and data from the GMOS spectrograph on the Gemini South telescope in Chile show that Omega Centauri appears to harbour an elusive and rare intermediate-mass black hole in its centre.
Astronomers may have discovered the first free-floating black hole in the Milky Way galaxy, thanks to a technique called gravitational microlensing. With new observations, they hope to find many more such ghost stars.
Unambiguous dynamical evidence for supermassive black holes exists only for a handful of galaxies; these include the Milky Way, the Local Group galaxies M31 and M32, and a few galaxies beyond the Local Group, such as NGC 4395.
IMBHs are an extremely rare subset of black holes that are larger than stellar-mass black holes but smaller than supermassive black holes. This means they can be anywhere between 100 and 100,000 times the mass of the sun, according to NASA.
The closest known black hole to Earth is a stone's throw away, just 1,600 lightyears distant. Dormant black hole Gaia BH1 lies only 1,600 lightyears away, making it the closest known black hole to Earth. The closest black hole to Earth is a stellar mass black hole just 1,600 lightyears away called Gaia BH1.
The James Webb Space Telescope (JWST) has detected two galaxies and their supermassive central black holes caught in a merging dance when the universe was only 740 million years old. This makes the find the farthest — and earliest — detection of merging black holes.
Stellar-mass binary black holes have been demonstrated to exist, by the first detection of a black-hole merger event GW150914 by LIGO. Duration: 1 second. 0:01 In this visualization a binary system containing two supermassive black holes and their accretion disks is initially viewed from above.
Hubble also demonstrated that galaxies farther away from us are receding faster than those nearby – a fundamental observation now known as Hubble's Law. The idea of an expanding universe is a key underpinning of the Big Bang Theory. Hubble's observations provided the earliest insight into the origins of our universe.
Einstein denied several times that black holes could form. In 1939 he published a paper that argues that a star collapsing would spin faster and faster, spinning at the speed of light with infinite energy well before the point where it is about to collapse into a Schwarzchild singularity, or black hole.
Despite their abundance, there is no reason to panic: black holes will not devour Earth nor the Universe. It is incredibly unlikely Earth would fall into a black hole because, at a distance, their gravitational pull is no more compelling than a star of the same mass.
Astronomers know that if they observe a distant star wobbling, it is orbiting a companion object. If that object is invisible and emitting x-rays, it could be a black hole. The star's distance from the x-ray source and the speed and magnitude of its wobble indicate the mass of the invisible object.
In a census performed by Hubble in the late 1990s, galaxies NGC 3379 and NGC 3377 were found to have black holes that “weighed in” at 50 million and over 100 million solar masses, respectively, and NGC 4486B was revealed to have a double nucleus at its core.
The negative square root solution inside the horizon represents a white hole. A white hole is a black hole running backwards in time. Just as black holes swallow things irretrievably, so also do white holes spit them out. White holes cannot exist, since they violate the second law of thermodynamics.
Similarly, the two other stars in the Alpha Centauri system, including Proxima Centauri, also have no chance of becoming black holes. The same is true for all the stars in the immediate vicinity of the Sun — they are not massive enough to even explode as supernovas, let alone leave behind a black hole.
The Milky Way has a big newfound black hole, and it lurks close to Earth! This sleeping giant was discovered with the European space telescope Gaia, which tracks the motion of billions of stars in our galaxy. Stellar-mass black holes are created when a large star runs out of fuel and collapses.
The resulting black hole that is left behind is referred to as a stellar mass black hole and its mass is of the order of a few times the mass of the sun. Not all stars leave behind black holes, stars with lower birth masses leave behind a neutron star or a white dwarf.
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