Astronomers confirmed an off-center black hole in a dwarf galaxy. It offers clues to how supermassive black holes may form.Black holes are most often assumed to sit at the centers of galaxies, but a team led by Dr. Tao An of the Shanghai Astronomical Observatory, Chinese Academy of Sciences, has identified one that breaks this rule. The researchers discovered a wandering black hole in a dwarf galaxy roughly 230 million light-years from Earth.
Unlike the central black holes typically observed, this one lies nearly a kiloparsec away from the galaxy’s core and is actively producing radio jets. Classified as an off-nuclear, accreting black hole, it represents one of the closest and most clearly confirmed examples known to date.
The findings, published online in Science Bulletin on September 4, add weight to the idea that black hole growth is not confined to galactic centers. This offers new insight into how supermassive black holes may have formed and expanded so rapidly in the early universe.
Black holes are often described as their “hearts.” Yet mounting evidence shows that some do not stay anchored in the center. Instead, these so-called wandering black holes drift through a galaxy’s disk or outer regions, resembling travelers lost in cosmic space.
Why search for wandering black holes in dwarf galaxies? These systems are less massive and have simpler evolutionary paths, making them valuable “cosmic fossils” that hold clues to the early stages of black hole growth. Theoretical models suggest that after galaxy mergers, or through complex multi-body interactions, gravitational recoil can easily eject black holes from the weak gravitational fields of dwarf galaxies, sending them thousands of light-years from their centers. Simulations even indicate that a significant portion of black holes in dwarf galaxies could be displaced by nearly a kiloparsec (about 3,000 light-years). Until recently, however, direct and unambiguous observational proof of this phenomenon had remained out of reach.
