Astronomers have found the first direct evidence that a wandering intermediate-mass black hole can feed itself by dragging gas along in its wake as it moves through its galaxy. This confirms a long-predicted accretion mechanism known as Bondi–Hoyle–Lyttleton accretion. The discovery, led by Xin Li of Westlake University in China, involves a black hole located in UGCA 320—an edge-on dwarf irregular galaxy roughly 20 million light-years away. A Hubble Space Telescope image revealed the object sat outside the galaxy's main star-forming disk. MUSE observations from 2021 detected broad Balmer emission, indicating an accreting massive black hole. Analysis showed the black hole's mass to be around 35,000 times the sun's mass, classifying it as an intermediate-mass black hole. Multiple independent observations support its identification as an accreting intermediate-mass black hole, or UGCA320-IMBH. The traits of this "wandering" black hole matched theoretical predictions. Intermediate-mass black holes, with masses between 100 and 100,000 times the sun, are thought to be seeds of supermassive black holes. Unlike their counterparts at galactic centers, wandering black holes lack mechanisms like galaxy mergers or tidal interactions to funnel gas toward them. The team's spectroscopic analysis revealed three components predicted by theory: low-density gas ahead of the black hole, denser gas trailing behind, and dense clumps tracing the accretion flow. This confirms the gravitational wake mechanism as a viable pathway for black hole growth.

The findings were posted to the arxiv preprint server on Aug. 11. Credit: ar Xiv (2026). DOI: 10.48550/arxiv.2608.10719