Wandering Supermassive Black Hole Discovered 600 Million Light-Years Away

This supermassive black hole was discovered thanks to the newly-identified tidal disruption event AT2024tvd, an astronomical phenomenon in which a star passes too close to a black hole and the extreme gravitational pull from the black hole shreds the star into thin streams of material.

“A tidal disruption event (TDE) happens when an infalling star is stretched or ‘spaghettified’ by a black hole’s immense gravitational tidal forces,” explained Dr. Yuhan Yao from the University of California at Berkeley and colleagues.

“The shredded stellar remnants are pulled into a circular orbit around the black hole.”

“This generates shocks and outflows with high temperatures that can be seen in ultraviolet and visible light.”

The AT2024tvd event allowed the astronomers to pinpoint a wandering supermassive black hole using the NASA/ESA Hubble Space Telescope, with similar supporting observations from NASA’s Chandra X-Ray Observatory, NRAO’s Very Large Array that also showed that the black hole is offset from the center of the host galaxy.

Surprisingly, this one million-solar-mass black hole doesn’t reside exactly in the center of the host galaxy, where supermassive black holes are typically found, and actively gobble up surrounding material.

Out of approximately 100 TDEs recorded by optical sky surveys so far, this is the first time an offset TDE has been identified.

In fact, at the center of the host galaxy there is a different supermassive black hole weighing 100 million times the mass of the Sun.

Hubble’s optical precision shows the TDE was only 2,600 light-years from the more massive black hole at the galaxy’s center.

That’s just one-tenth the distance between our Sun and the Milky Way’s central supermassive black hole.

This bigger black hole spews out energy as it accretes infalling gas, and it is categorized as an active galactic nucleus.

Strangely, the two supermassive black holes co-exist in the same galaxy, but are not gravitationally bound to each other as a binary pair.

The smaller black hole may eventually spiral into the galaxy’s center to merge with the bigger black hole.

But for now, it is too far separated to be gravitationally bound.

“AT2024tvd is the first offset TDE captured by optical sky surveys, and it opens up the entire possibility of uncovering this elusive population of wandering black holes with future sky surveys,” Dr. Yao said.

“Right now, theorists haven’t given much attention to offset TDEs.

“I think this discovery will motivate scientists to look for more examples of this type of event.”

The black hole responsible for AT2024tvd is prowling inside the bulge of the massive galaxy.

The black hole only becomes apparent every few tens of thousands of years when it burps from capturing a star, and then it goes quiet again until its next meal comes along.

How did the black hole get off-center? Previous theoretical studies have shown that black holes can be ejected out of the centers of galaxies because of three-body interactions, where the lowest-mass member gets kicked out.

This may be the case here, given the stealthy black hole’s close proximity to the central black hole.

“If the black hole went through a triple interaction with two other black holes in the galaxy’s core, it can still remain bound to the galaxy, orbiting around the central region,” Dr. Yao said.

An alternative explanation is that the black hole is the surviving remnant of a smaller galaxy that merged with the host galaxy more than one billion years ago.

If that is the case, the black hole might eventually spiral in to merge with the central active black hole sometime in the very far future. So at present, astronomers don’t know if it’s coming or going.

“There is already good evidence that galaxy mergers enhance TDE rates, but the presence of a second black hole in AT2024tvd’s host galaxy means that at some point in this galaxy’s past, a merger must have happened,” said Dr. Erica Hammerstein, also from the University of California at Berkeley.

The team’s findings will be published in the Astrophysical Journal Letters.

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Yuhan Yao et al. 2025. A Massive Black Hole 0.8 kpc from the Host Nucleus Revealed by the Offset Tidal Disruption Event AT2024tvd. ApJL, in press; arXiv: 2502.17661