Every massive galaxy astronomers have ever seen has a supermassive black hole at its centre. Some, though, ought to have so-called wandering supermassive black holes closer to their outskirts, too, and researchers have just spotted the most extreme example ever found.
True to their names, black holes don鈥檛 emit light, so at the University of Maryland and his team spotted this one only when it devoured a star in what鈥檚 known as a tidal disruption event, or TDE. A machine learning algorithm identified the burst of light as a possible TDE in data from the Zwicky Transient Facility (ZTF) in California, and the researchers performed follow-up observations with several other telescopes to confirm it.
This TDE, called TDE 2025abcr, is the most distant from the centre of its host galaxy that we鈥檝e ever seen. 鈥淲e have a couple of examples of a tidal disruption event that鈥檚 very close to the centre of a galaxy but a little offset, and then we have examples where there鈥檚 a big galaxy and a little dwarf galaxy merging with it, and that dwarf galaxy has a TDE. This is just an empty patch of sky as far as we can tell,鈥� says Stein. It is more than 30,000 light years from the centre of its galaxy 鈥� for comparison, our solar system is about 26,000 light years from the centre of the Milky Way.
Advertisement
Wandering supermassive black holes usually begin their journeys away from a galactic centre due to a merger: two galaxies slam together, and one of their central black holes is flung away. Finding these black holes can tell us about the history and growth of their galaxies. 鈥淲hat鈥檚 exciting about this result is that we think it鈥檚 the tip of the iceberg,鈥� says Stein. 鈥淚f we can understand how many wandering supermassive black holes there are, then it can tell us about how many mergers the galaxy has been through and how it鈥檚 evolved over time.鈥�
Black holes鈥� dark nature means that it is extremely difficult to find them; it is mostly accomplished by projects like ZTF that monitor the whole sky for flashes of light. The latest of these projects, the Legacy Survey of Space and Time (LSST) at the Vera Rubin Observatory in Chile, has just begun and is expected to find hundreds more in the coming years, Stein says.
In the meantime, there is a limit to how much we can learn about this particular black hole and its environs. The light from the star being devoured is still too bright to see much of anything else around it. 鈥淪ome TDEs can last for years and years, so we might have to wait a long time to uncover what鈥檚 really going on here,鈥� says Stein.聽聽
Most likely there is a small cluster of stars that is gravitationally tied to the black hole, and one of those caused the TDE as it fell in, but we can鈥檛 confirm that until the light fades. At least we don鈥檛 have to worry about black holes lurking near Earth, because the sun isn鈥檛 in such a cluster, Stein says: 鈥淚 think it鈥檚 very, very unlikely that this is going to happen to our star.鈥�
The Astrophysical Journal Letters
