A team of international astronomers, expert hunters of black holes, decided to search for supermassive black holes not only at the center of galaxies where they are typically detected but anywhere in the patch of night sky scanned by the Zwicky Transient Facility. Just three months later, they stumbled upon one such black hole lurking on the edge of a galaxy. It’s the first time scientists have detected a dormant black hole so far away from a galaxy’s center.

The only way to detect black holes with optical telescopes is to catch them in the act of swallowing a nearby star that is sucked into the black hole's gravitational pull. Such events, known as tidal disruption events (TDEs) are well studied. Black holes discovered via TDEs are generally residing at the center of galaxies and the ZTF partnership alone has discovered more than eighty such events in the last eight years since ZTF became operational.

We have developed advanced algorithms to search for TDEs that we have tested and refined during the course of ZTF. When we decided to use them to search for black holes in ZTF data outside galaxy centers, we weren't really sure we would be successful so quickly, so it's amazing that we found one so fast, says study lead author Robert David Stein, 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).

The black hole described in this study is located 9.3 kiloparsecs (about 30,000 light-years) away from the center of its galaxy. It’s about the same mass as the black hole at the center of our galaxy, the Milky Way. But surprisingly, it has no observable galaxy swirling around it.

This black hole likely originated from two colliding galaxies. One possibility is that a larger galaxy cannibalized a smaller one and then slowly stripped away its stars until only the core remained.

A second possibility is that one galaxy already had two black holes orbiting closely at its center—this is called a binary black hole. If a third black hole from another merger enters the mix, complex three-body interactions would kick the smallest one out. Continued observations of this tidal disruption event could favor one of these two theories over the other, the authors said.

We will continue to scan the skies for more such objects so that we can better understand how galaxies form and how many black holes are whizzing around. We’ve learned a lot about discovering TDEs from ZTF in the past 8 years. Now that we have perfected the formula, we are looking forward to using the high cadence of ZTF in combination with the unmatched sensitivity of the newly launched Rubin LSST survey to discover many more off-nuclear TDEs across the sky. Rubin’s improved precision will also help to identify TDEs with much smaller offsets than TDE 2025abcr.

It is super exciting, says Suvi Gezari, an associate professor of astronomy at UMD who is a co-author on the paper and a partner in the ZTF consortium. It’s an example of how machine learning and AI can help to find many more examples of wandering black holes advancing our understanding of how galaxies and their black holes merge and build up over time.

Read full UMD press release.

The paper, “TDE 2025abcr: A Tidal Disruption Event in the Outskirts of a Massive Galaxy,” was published in The Astrophysical Journal Letters on July 27, 2026.

ZTF is funded by the U.S. National Science Foundation award #2407588 and support from partner institutions.

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