A supermassive black hole does not have to sit at the centre of its galaxy. Astronomers at the University of Maryland have now found one far outside. It lies around 30,000 light years from its galaxy's core. That is roughly the distance from the Sun to the centre of the Milky Way. The study appeared on 27 July in the "Astrophysical Journal Letters".
Dormant black holes emit no light. They become visible almost only when their tidal forces tear a star apart. That event is called a tidal disruption event, or TDE. It flares briefly and then fades slowly. On average it happens once every 100,000 years per galaxy. Researchers know of about a hundred such outbursts so far, and nearly all came from galactic centres.
An AI combed the night sky
The team around Robert Stein therefore changed the search strategy. It trained an algorithm on the characteristic light pattern of a TDE. From August 2025 the program worked through data from the Zwicky Transient Facility at the Palomar Observatory in California. Its two telescopes scan the northern sky every two days. The software checked some 500,000 variable objects a night. After three months it flagged a hit far from any galactic core.
The event is designated TDE 2025abcr and sits in a galaxy about 750 million light years away. Follow-up observations with further instruments ruled out other explanations, says co-author Jonathan Carney of the University of North Carolina at Chapel Hill. The black hole weighs in at roughly four million solar masses. That makes it as heavy as Sagittarius A* at the heart of the Milky Way. Older images show nothing at its position. "You would not have suspected a black hole was hiding there," Stein says.
How did it get there? The researchers suspect a galactic merger. A smaller galaxy was torn apart by the larger one and left its black hole behind. A recoil from the merger of two black holes fits the data less well, "Sky & Telescope" reports. The object moves barely differently from its host galaxy.
How many such wanderers exist remains open. Suvi Gezari, also of the University of Maryland, regards the find as the first of a series. Their number would reveal how often a galaxy has merged over its history. An independent group around Kishore Patra of the University of California, Santa Cruz has already observed the object with the Keck telescopes and the James Webb Space Telescope. Their analysis exists so far only as a preprint and has not been peer reviewed.