For the first time, astronomers have observed a violent galactic duel in which one galaxy uses a quasar to bombard another with intense radiation, impeding its ability to form new stars. This discovery, detailed in Nature, offers unprecedented insight into how galaxy collisions and supermassive black holes influence cosmic evolution.
Two galaxies, locked in a cataclysmic collision, are charging at each other at speeds of 500 km/s, striking glancing blows before retreating—only to clash again in an ongoing cosmic joust.
Study co-lead Pasquier Noterdaeme of the Institut d’Astrophysique de Paris likened the encounter to medieval combat, with one side wielding a deadly advantage: a quasar-powered radiation spear.
Quasars—the blazing cores of galaxies that actively feed supermassive black holes—release tremendous energy and can reshape entire galaxies. Though common in the Universe’s early days, they are rarely observed in the act of altering a neighboring galaxy’s fate.
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Because this battle occurred over 11 billion years ago, its light has only recently reached Earth, offering a glimpse into an era when the Universe was just 18% of its current age.
This study marks the first time astronomers have directly observed how a quasar’s radiation disrupts another galaxy’s structure. Using the X-shooter instrument on the Very Large Telescope (VLT) and ALMA’s powerful imaging capabilities, the team found that radiation from the quasar scatters the larger gas clouds needed to form stars, leaving behind only dense fragments that may be too small to continue star formation.
“The quasar’s radiation essentially stops the wounded galaxy from forming new stars,” explained Sergei Balashev, co-lead researcher at Russia’s Ioffe Institute. “It’s a dramatic transformation, stripping away its future as a stellar nursery.”
While one galaxy suffers, the black hole at the heart of the quasar grows stronger. As the galaxies collide, fresh material is funneled toward the black hole, feeding the quasar and allowing it to continue its destructive assault.
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“These mergers bring enormous amounts of gas to supermassive black holes,” Balashev noted. “As the black hole devours this fuel, the quasar intensifies, becoming an even more formidable cosmic force.”
Thanks to ALMA’s high-resolution imaging, scientists could distinguish the two merging galaxies, which had previously appeared as a single blurred object. Future observations with larger telescopes, like ESO’s Extremely Large Telescope, could reveal even more details about this battle and similar cosmic clashes.
Noterdaeme is optimistic about future studies, saying, “Bigger telescopes will allow us to deepen our understanding of how quasars shape galaxies during collisions, helping to unravel their role in cosmic evolution.”
Journal Reference:
- Sergei Balashev, Pasquier Noterdaeme et al. Quasar radiation transforms the gas in a merging companion galaxy. Paper
