University of Maryland astronomers have identified a dormant supermassive black hole positioned far from the center of its host galaxy. The discovery marks the first time scientists have found an inactive black hole at such a great distance from a galactic core.
Because the black hole was not actively consuming matter, it would ordinarily have remained invisible. Its location was exposed only when it tore apart a passing star, producing a brief but powerful burst of light. The findings were published in The Astrophysical Journal Letters on July 27, 2026.
“This is a novel result. What’s new is that, until now, we’ve started with the assumption that supermassive black holes reside in the centers of massive galaxies,” said study co-author Suvi Gezari, an associate professor of astronomy at UMD. “This discovery will have a huge impact. It means that we’re going to find many more examples of wandering black holes, and we can understand how galaxies and their black holes merge and build up over time.”
A Long Predicted Wandering Black Hole
Scientists have long predicted that some black holes could be displaced toward the outer regions of galaxies during galactic collisions and mergers. These objects are often described as “wandering” black holes.
Finding them is extremely difficult. Many are quiescent, meaning they are not consuming nearby material or producing detectable light. As a result, they can move through galactic outskirts without being noticed by telescopes on Earth.
Researchers first detected the quiescent black hole using the Zwicky Transient Facility (ZTF), which “searches the whole universe,” according to study lead author Robert David Stein. Stein is a Neil Gehrels Prize Postdoctoral Fellow at the Joint Space-Science Institute, a research partnership between UMD’s Departments of Astronomy and Physics and NASA’s Goddard Space Flight Center (GSFC).
Artificial Intelligence Finds a Stellar Flare
Using two telescopes at Palomar Observatory in San Diego County, California, ZTF surveys the entire northern sky once every two days. The observatory records hundreds of thousands of changing celestial events each night, making it impractical for researchers to examine every event individually for signs of a black hole.
To handle that enormous volume of data, the team created an artificial intelligence (AI) program trained to recognize the distinctive light pattern produced when a black hole destroys a star. This event, known as a tidal disruption event, occurs when a star passes close enough to be pulled apart by a black hole’s gravity.
Astronomers have documented many tidal disruption events near the centers of galaxies. The new AI system was designed to search for the same types of flares across the entire sky, including locations far from galactic centers.
The UMD researchers began operating the program in August 2025. Only three months later, it identified the event that led them to the wandering black hole.
“I remember the moment we discovered it very clearly. It was a Saturday, and everyone was very excited to be messaging. We dropped everything and started triggering all kinds of other instruments to get more data,” Stein said. “We weren’t really sure we would be successful so quickly, so it’s amazing that we found one so fast.”
A Supermassive Black Hole Far From the Galactic Center
The black hole sits 9.3 kiloparsecs (about 30,000 light-years) from the center of its galaxy. Its mass is comparable to that of the supermassive black hole located at the center of the Milky Way.
What makes the object especially puzzling is the apparent absence of a visible galaxy surrounding it, according to study co-author and UMD Astronomy Professor Sylvain Veilleux.
“To have such a big black hole outside of a galaxy is surprising to me,” he said. “There should be a Milky Way-like object around it — and that’s definitely not the case.”
Researchers believe the black hole’s unusual position is probably connected to a past collision between galaxies.
One explanation is that a large galaxy absorbed a smaller companion. Over time, the larger galaxy may have stripped away nearly all of the smaller galaxy’s stars, leaving only its dense central core and black hole behind.
Another possibility involves a more chaotic encounter among three black holes. A galaxy may already have contained two black holes orbiting closely around one another at its center, a system known as a binary black hole. If a third black hole arrived during another galactic merger, the resulting three-body interaction could have expelled the smallest black hole from the center.
Additional observations of the tidal disruption event may help researchers determine which explanation is more likely.
Dormant Black Holes Could Be Common
Understanding inactive black holes is important because most known black holes are dormant, including the one at the center of the Milky Way.
Scientists do not yet know whether wandering black holes exist in the outer regions of our own galaxy. However, Stein said there is no reason to worry about encountering one.
“We’re very unlikely to meet one, at least in our lifetime.”
The research team is continuing to search the sky for additional wandering black holes. Finding more of them could help scientists “understand how galaxies form and how many black holes are whizzing around,” Stein said.
The discovery also demonstrates that these elusive objects can be identified with conventional sky surveys combined with machine learning, rather than relying exclusively on more expensive observational methods.
“It is super exciting,” Gezari explained. “It’s an example of machine learning opening up a whole new area of research.”
New Observatories Could Find Hundreds More
Stein expects future searches with the NSF-DOE Vera C. Rubin Observatory to identify dozens or possibly hundreds of wandering black holes each year. The Chile-based observatory debuted last June and captures exceptionally detailed views of the sky with the world’s largest digital camera.
Veilleux also pointed to the Lowell Discovery Telescope and its Rapid infrared IMAger-Spectrometer, which debuted in June 2025 as a collaboration between GSFC, the UMD Department of Astronomy and Lowell Observatory. The instrument could enable scientists to detect tidal disruption events at far greater distances from Earth than previously thought possible.
“This is the strongest case of a wandering black hole that we know,” Veilleux said. “This is going to set the standard.”
UMD Astronomy Adjunct Professor Stephen Bradley Cenko and postdoctoral associate Jillian Chin Rastinejad coauthored the study with Stein, Gezari and Veilleux.
This research was funded by the U.S. National Science Foundation (Award Nos. 2407588 and 1106171); the Gordon and Betty Moore Foundation through the Data-Driven Investigator Program and a dedicated grant to SkyPortal; the W. M. Keck Foundation; the Heising-Simons Foundation; William and Marina Kast; the University of California Observatories; Google; Deutsche Forschungsgemeinschaft under Germany’s Excellence Strategy, EXC-2094/2, 390783311.939; the Australian Research Council under ARC LIEF grant LE130100104; Astronomy Australia Limited and the Australian Government through the Commonwealth’s Education Investment Fund and National Collaborative Research Infrastructure Strategy, particularly the National eResearch Collaboration Tools and Resources and the Australian National Data Service Projects. This content does not necessarily reflect the views of these parties and organizations.
