Astronomers have captured a rare cosmic encounter in which a galaxy armed with a powerful quasar bombards a companion, drastically altering its ability to form stars. The discovery, detailed in Nature, showcases a previously unseen phenomenon of quasar radiation interfering with galactic star formation.
Using data from the European Southern Observatory's Very Large Telescope (VLT) and the by Robert Schreiber
Berlin, Germany (SPX) May 22, 2025
Astronomers have captured a rare cosmic encounter in which a galaxy armed with a powerful quasar bombards a companion, drastically altering its ability to form stars. The discovery, detailed in Nature, showcases a previously unseen phenomenon of quasar radiation interfering with galactic star formation.
Using data from the European Southern Observatory's Very Large Telescope (VLT) and the Atacama Large Millimeter/submillimeter Array (ALMA), researchers observed two galaxies locked in a gravitational skirmish. The pair repeatedly rush toward each other at about 500 km/s, exchanging glancing blows before recoiling for another charge. "We hence call this system the 'cosmic joust'," said Pasquier Noterdaeme of the Institut d'Astrophysique de Paris and the French-Chilean Laboratory for Astronomy.
In this dramatic intergalactic duel, one galaxy holds an advantage-a blazing quasar at its core. Quasars, which are the luminous centers of some galaxies powered by supermassive black holes, release torrents of energy. That energy, the researchers found, is lancing through the other galaxy, stripping away its potential for new stars by disrupting its internal gas structure.
"This is the first time we've directly observed the effect of a quasar's radiation on the inner gas of a regular galaxy," noted Sergei Balashev of the Ioffe Institute in St Petersburg. The radiation leaves behind only compact, dense gas clouds-insufficient for large-scale star formation.
The encounter also benefits the quasar's host galaxy. As Balashev explained, galaxy mergers can funnel massive amounts of gas toward central black holes, intensifying quasar activity and reinforcing the destructive radiation assault.
The team relied on ALMA's precision to distinguish the two galaxies, previously indistinguishable as a single object. ESO's X-shooter instrument then enabled them to dissect the quasar's light as it passed through the injured galaxy, revealing how deeply the radiation affected the gas composition.
Future studies with next-generation observatories like ESO's Extremely Large Telescope could expand on these findings. "It will certainly allow us to push forward a deeper study of this, and other systems," said Noterdaeme, "to better understand the evolution of quasars and their effect on host and nearby galaxies."
Research Report:Quasar radiation transforms the gas in a merging companion galaxy
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