Some 1.2 billion light-years away, a system called J1218/1219+1035 hosts not one, but three galaxies spiraling into a common merger.

 

Some 1.2 billion light-years away, a system called J1218/1219+1035 hosts not one, but three galaxies spiraling into a common merger.

At the heart of each galaxy lies a supermassive black hole actively feeding, lighting up as a radio-bright active galactic nucleus (AGN). Triple galaxy encounters are rare; triple active nuclei are rarer still.

The system was first flagged in data from NASA’s Wide-field Infrared Survey Explorer (WISE), where it initially appeared as a merger between two galaxies, each with its own AGN. Follow-up radio observations then revealed a third galaxy joining the dance, its black hole blazing and linked to the others by a tidal tail of gas.

Measurements show the two overlapping galaxies are separated by about 74,000 light-years, while the third sits roughly 316,000 light-years away, connected by a stream of material flowing toward the pair. All three black holes are launching powerful jets, making this the first known case in the nearby Universe where every member of a triple merger hosts a radio-bright AGN.

By catching this system mid-merger, astronomers gain a rare laboratory to study how galaxies and their central black holes grow together across cosmic time. Future multiwavelength observations will search for more hidden triples, refining how galaxy assembly and black hole evolution unfold in the most extreme environments.

RESEARCH PAPER

E. Schwartzman et al., “The First Triple Radio Active Galactic Nucleus in an Ongoing Galaxy Merger.” The Astrophysical Journal Letters (2025)

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