Omega Centauri: The core of the galaxy frozen in time reveals its black hole

The researchers confirmed a moderate mass The black hole at the center of Omega Centauri, supporting theories of its origin as the core of a separate galaxy that collided with. the universe. . . .

Newly identified fast-moving stars in the Omega Centauri cluster of stars provide solid evidence for a central black hole in the cluster. At at least 8,200 solar masses, it is the best candidate for a class of black holes that astronomers have long thought existed: intermediate-mass black holes, formed during the early stages of galactic evolution. The discovery strengthens the case for Omega Centauri as the core region of a galaxy that was swallowed by the Milky Way billions of years ago. It is the core of the galaxy, stripped of its outer stars, remaining “frozen in time” ever since. The study was published in the journal Nature.

Finding the heart of Omega Centauri

Omega Centauri is a spectacular cluster of about ten million stars, visible as a speck in the night sky from southern latitudes. Through a small telescope, there is no difference from other clusters called spherical clusters: groups of spherical stars, towards the center so dense that it becomes impossible to distinguish individual stars.

But now a new study led by Maximilian Haberl (Max Planck Institute for Astronomy) confirms what cosmologists have suspected for some time: Omega Centauri contains a central black hole. The black hole appears to be the “missing link” between stellar relatives and superlarge relatives: it is trapped in an intermediate stage of evolution, much smaller in size than normal black holes in the centers of galaxies. Omega Centauri is believed to be the core of a small, isolated galaxy whose evolution was cut short when the Milky Way swallowed it up.

The spectrum of black holes

In astronomy, black holes come in a range of different masses. Stellar black holes, between one and several tens of solar masses, are well known, as are supermassive black holes with masses of millions or even billions of suns. Our current picture of galaxy evolution assumes that the earliest galaxies would have had intermediate-sized black holes, which grew over time as those galaxies evolved, gobbling up smaller galaxies (as our Milky Way did) or merging with larger ones.

These medium-sized black holes are notoriously hard to find. Galaxies like our own Milky Way have long outgrown that central period and now contain much larger central black holes. The galaxies that remain small (“dwarf galaxies”) are generally difficult to observe. With the technology now available, monitoring their central regions that can detect the central black hole is extremely challenging. Although there are promising candidates, there has been no definite discovery of such a moderate-mass black hole – until now.

This zoom video begins with an overview of the sky and ends with a picture of. Hubble Space Telescope at the Omega Centauri Center. Finally, the orbits of the stars around the black hole are shown. Credit: T. Müller (MPIA/HdA), Music: K. Jäger (MPIA)

A galaxy (Core) frozen in time

This is what makes Omega Centaur special. If it was once the core of a separate galaxy, which then merged with the Milky Way and lost all but its central batch of stars in the process, the remaining core and its central black hole would be “frozen in time”: there should be no more mergers, and no way for central black hole development. The black hole is maintained at the size it was when Omega Centauri was swallowed by the Milky Way, providing a glimpse into the missing connection between early low-mass black holes and later supermassive black holes.

To test this hypothesis, it is necessary to actually detect a central black hole in Omega Centauri, and a certain discovery had eluded astronomers until now. While there was evidence from large-scale models of stellar motion in the cluster, that evidence left room for doubt: there may not have been a central black hole at all.

This video shows schematically how Omega Cen was observed with the Hubble Space Telescope. You can see the position of the camera detector during 800 individual images. Finally, it shows the picture that cosmologists have created from the contacts. Credit: M. Häberle (MPIA)

A breakthrough in the detection of black holes

When Nadine Neumeier, a group leader at the Max Planck Institute for Astronomy, and Anil Seth of the University of Utah devised a research project aimed at improving understanding of Omega Centauri’s formation history in And settle it forever: If they could identify the expected fast stars around a black hole at the center of Omega Centauri, it would be the proverbial smoking gun, as well as a way of measuring the mass of the black hole.

The arduous search became the task of Maximilian Haberly, a doctoral student at the Max-Planck Institute for Astronomy. Huberl led work on creating a massive catalog of stellar motion at Omega Centauri, measuring the velocities of 1.4 million stars by studying more than 500 Hubble images of the cluster. Most of these images were produced for the purpose of calibrating the Hubble instruments rather than for scientific use. But thanks to their ever-recurring views of Omega Centauri, they turned out to be an ideal dataset for the team’s research efforts.

“Looking for fast stars and documenting their movements was the proverbial search for a needle in a haystack,” says Haberl. Finally, however, Haberl not only had the most complete catalog of stellar motions in Omega Centauri to date (published in a separate article). He had also found not one but seven needles in the haystack of his archives: seven fast-moving narrative stars in a small area at the center of Omega Centauri.

Revealing a black hole

Fast moving stars are fast due to the presence of dense mass nearby. For a single star, it’s impossible to tell if it’s accelerating because the central mass is large or because the star is so close to the central mass – or if the star is just flying vertically, with no mass in sight. But seven such stars, at different speeds and directions of motion, allowed Haberl and his colleagues to separate out different effects and determine that there is a central mass in Omega Centauri, with a mass of at least 8,200 suns. The images do not indicate anything visible at the ejected location of that central mass, as one would expect for a black hole.

The broader analysis not only enabled Haberl to pinpoint the velocity of his fast seven stars. It also located just where the central area, three light moons in diameter (on the photos, three arc seconds), narrowed inside Omega Centauri. Furthermore, the analysis provided statistical certainty: a single fast star in the image may not even belong to Omega Centauri. It could be a star outside the orbit that happens to pass right behind or in front of Omega Centauri’s center. Observations of seven such stars, on the other hand, cannot be pure coincidence and leave no room for explanation other than a black hole.

An intermediate mass black hole at the end

“Previous studies provoked the critical question of ‘So where are the fast stars?’” Neumeyer said. Now we have an answer to that and confirmation that Omega Centauri contains a medium-mass black hole. At a distance of about 18,000 light-years, this is the closest known example to a massive black hole.” The supermassive black hole at the center of the Milky Way is about 27,000 light-years away. The discovery not only promises to resolve the decade-long debate about a medium-mass black hole in Omega Centauri. It also provides the best candidate so far for detecting an intermedia mass black hole as a whole.

Given their findings, Neumeier, Haberl and their colleagues now plan to examine Omega Centauri’s center in greater detail. They already have approval to measure the accelerated star’s motion towards or away from Earth (line-of-sight velocity) using. James Webb Space Telescopeand there’s the next machine (GRAVITY+ at that‘s VLT, MICADO at the Extremely Large Telescope) that can locate stars more accurately than Hubble. The long-term goal is to determine how stars accelerate: how their orbits are curved. However following those stars once around their entire orbit, as in the Nobel Prize-winning observation near the black hole in the middle of the Milky Way, is a project for future generations of astronomers. Smaller black hole masses for Omega Centauri mean ten times larger time scales than the Milky Way: orbital periods of more than a hundred years.

background information

The work described here is titled M. Häberle et al., “Fast Moving Stars Around an Intermediate-Mass Black Hole in ω Centauri” published in the journal nature. . . . The star catalog on which the work is based has been accepted for publication as M. Häberle et al., “oMEGACat II — photometry and proper motion for 1.4 million stars in Omega Centauri and rotation in the celestial plane” in. Journal of Astrophysics. . . .

For more on this discovery, see Missing Link Uncovered: Hubble Unveils Hidden Black Hole in Omega Centauri.

resources:

“Fast-Moving Stars Around a Medium-Mass Black Hole at ω Centauri,” by Maximilian Haberl, Nadine Neumeier, Anil Seth, Andrea Bellini, Mattia Liberato, Holger Baumgart, Matthew Whitaker, Anton Dumont, Mait Alfaro-Cuello, Jay Anderson, Callie Klontz, Nikolai Kacharov, Sebastian Kaman, Anja Feldmeier-Krauss, Antonino Milone, Maria Celina Nitschya, Renoka Pecchetti and Glen van de Ven, July 10, 2024, nature. . . .
doi: 10.1038/s41586-024-07511-z

“oMEGACat II — Photometry and Proper Motions for 1.4 Million Stars in Omega Centauri and Rotation in the Plane of the Sky” by Maximilian Haberl, Nadine Neumeier, Andrea Bellini, Mattia Liberato, Kali Clontz, Anil C. Schmidt, and R.J. Seth, Maria Selena Nitschya, Sebastian Kaman, Maite Alfaro-Cuello, Jay Anderson, Stephane Drezler, Anja Feldmeier-Krauss, Nikolai Kacharov, Marilyn Latour, Antonino Milone, Renoka Pecchetti, Glen van de Ven, Karina Vogel, quoted, Journal of Astrophysics. . . .
arXiv:2404.03722

MPIA scholars involved are Maximilian Haberl, Nadine Neumeier, Anton Dumont, Callie Klontz (also University of Utah), Anja Feldmeier-Krauss (also University of Vienna) and Maria Celina Nitsch, in collaboration with Anil Seth (University of Utah), Andrea Bellini (Institute of Space Telescope Science). Potsdam Astrophysics), Sebastian Kaman (Liverpool John Moores University), Antonino Milone (University of Padua), Renuka Pecchitti (Liverpool John Moores University) and Glen van de Ven (University of Vienna).