Rare black hole event discovered outside the galaxy

The Zwicky Transient Facility (ZTF) detected an unusual brightness in the sky in 2024. This object, called AT2024tvd, appeared 2,500 light-years away from the galactic centers where supermassive black holes are typically found.

So how does this discovery add a piece to the cosmic puzzle? Initially, automated systems didn’t flag the object as a black hole. But data from the Hubble and Very Large Array telescopes revealed the destruction of a star by a wandering black hole. Here’s how it happened… The star succumbed to the black hole’s tidal forces. Its inner layers were pulled into the black hole in a spiral pattern, emitting bright radiation across the electromagnetic spectrum.

Unlike a supernova, the light did not fade over time because the star's material continued to fall into the black hole, Chip said.

This process was identified as a Tidal Disruption Event (TDE). But the question was: Why was the black hole so far from the galactic center?

How do black holes become "travelers"?

The answer lies in the dynamics of galaxy mergers. Larger galaxies grow by swallowing smaller galaxies. However, during these mergers, one of the black holes can be ejected from the galactic center. Gravitational interactions force the black hole into a slow drift within the galaxy. AT2024tvd is thought to have been “exiled” in this way.

These types of wandering black holes are not the only ones of their kind. Theorists suggest that there could be more than a dozen drifting black holes in massive galaxies. The larger the galaxy, the more likely it is to host these “rogue” black holes.

Supermassive black holes can swallow stars without emitting light at their event horizons. However, wandering black holes allow us to observe the final moments of stars due to their smaller mass and dynamic position. AT2024tvd provided this rare opportunity, prompting scientists to ask: Are there similar wandering black holes in our Milky Way galaxy; could these events open a new window into understanding the evolution of black holes?

AT2024tvd illuminates not only the destruction of a star, but also the history of galaxy mergers. The researchers predict that future telescope surveys (such as the Vera Rubin Observatory) will detect such events more frequently, revolutionizing mapping the universe’s black hole population.

Wandering black holes may be the unseen architects of galaxies. AT2024tvd is just the beginning of tracking down these “shadow hunters”...