'Surprising and exciting': U. astronomers harness NASA telescopes for black hole discovery
by Logan Stefanich ksl · KSL.comKEY TAKEAWAYS
- University of Utah astronomers discovered a stellar-mass black hole in the Omega Centauri star cluster.
- They used NASA's Hubble and Webb telescopes to measure star movements over time.
- The black hole, oMEGACat BH-2, has a surprising low mass and long orbital period.
SALT LAKE CITY — In a discovery that has eluded and puzzled astronomers for centuries, University of Utah astronomers harnessed archival data from NASA's Hubble Space Telescope and observations from NASA's James Webb Space Telescope to locate the first stellar-mass black hole in the massive globular star cluster Omega Centauri.
The team's findings, published Monday in The Astrophysical Journal Letters, challenge the very idea of how black holes form within environments like Omega Centauri.
Composed of 10 million gravitationally bound stars, models suggested the Omega Centauri star cluster contained about 10,000 smaller, stellar-mass black holes. The problem?
This black hole population had evaded detection until U. researchers employed a different approach, known as astrometry, to measure very small movements of stars over time.
The team sifted through over 20 years of Hubble archival data, coupling it with more recent Webb data to further refine their astrometric measurements. In doing so, the team located a star orbiting an invisible object so substantial that it couldn't have been anything but a black hole.
Dubbed oMEGACat BH-2, it is the first stellar-mass black hole detected in Omega Centauri. It also has some surprising qualities, including a lower-than-expected mass, and, with its visible star companion, the black hole-star duo has the longest orbital period of any black hole binary system known to date, according to the research.
"With Hubble and Webb data, we were able to see the motion of the visible main-sequence star that is part of this binary, which is about 18,000 light-years away in the dense environment of Omega Centauri," Matthew Whitaker, undergraduate research assistant at the University of Utah and lead author of the paper, said in a statement. "The precision of these measurements is incredible, down to a fraction of a pixel on Hubble and Webb's detectors. It would not have been possible to find this black hole without these two space telescopes."
The U. team's findings also build upon a past study by a different group of scientists suggesting this binary system included a neutron star. By combining the two data streams, the U.-led team was able to better constrain the mass of the visible star's dark companion and rule out the possibility of a neutron star.
"While we already knew that the star was 0.78 solar masses, we can now calculate the black hole's mass, which is 4.46 solar masses and therefore too heavy to be a neutron star. However, its mass is much lower than would be expected in a metal-poor environment like Omega Centauri. This is surprising and exciting," Anil Seth, professor of physics and astronomy at the University of Utah and coauthor of the study, said in a statement. "We now know that a metal-poor star is able to form a black hole like this, and we need to figure out how that happens. This detection is providing some data to those who do that kind of modeling."
Based on the more precise data from Hubble and Webb, the researchers could chart the star's path over 20-plus years, during its closest approach to its black hole companion when it moved the fastest across the sky. The team determined that the visible star orbits oMEGACat BH-2 once every 94 years, making it the longest-period black hole binary ever known.
The discovery of the orbital period also clued the team into the potential origin of this particular binary system, suggesting it was likely dynamically formed, meaning the star and its black hole companion did not start out together but rather found each other in this cluster.
Additionally, the researchers calculated that a system like oMEGACat BH-2 will survive for less than a billion years before it is torn apart by encounters with nearby stars, a much shorter span than the age of the cluster (approximately 12 billion years old), according to the research.
The discovery, though, is likely only the start of finding elusive black hole populations in globular star clusters.
"With Hubble and Webb, we can continue to look at Omega Centauri and expand our search for similar systems within other clusters," Whitaker said in a statement. "We're also very excited for the launch of NASA's Nancy Grace Roman Space Telescope because it will image the crowded galactic bulge, including the galactic center, very regularly with Hubble-like resolution and with a much wider field of view. We're hoping we'll be able to find black hole binary systems like this one because of the regular cadence of Roman's observations."
The team's full findings can be found here.
The Key Takeaways for this article were generated with the assistance of large language models and reviewed by our editorial team. The article, itself, is solely human-written.
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Logan Stefanich
Logan Stefanich is a reporter with KSL, covering northern Utah communities, education, business and tech news.