Free Astronomy Magazine July-August 2025

38 JULY-AUGUST 2025 ASTRO PUBLISHING T his wide-field view shows the re- gion of the sky around a pair of interacting galaxies, nicknamed the ‘cosmic joust’, in which one of them is piercing the other with intense ra- diation. The galaxies appear as a tiny white dot at the centre of this image. The Atacama Large Millimeter/sub- millimeter Array (ALMA) resolved them in great detail, and ESO’s Very Large Telescope (VLT) studied the damage that one galaxy is inflicting on the other. [DESI Legacy Survey] ducted using ALMA and the X- shooter instrument on ESO’s VLT, both located in Chile’s Atacama Desert. ALMA’s high resolution helped the astronomers clearly dis- tinguish the two merging galaxies, which are so close together they looked like a single object in previ- ous observations. With X-shooter, researchers ana- lysed the quasar’s light as it passed through the regular galaxy. This al- lowed the team to study how this galaxy suffered from the quasar’s radiation in this cosmic fight. Observations with larger, more pow- erful telescopes could reveal more about collisions like this. As Noter- daeme says, a telescope like ESO’s Extremely Large Telescope “will cer- tainly allow us to push forward a deeper study of this, and other sys- tems, to better understand the evo- lution of quasars and their effect on host and nearby galaxies.” too small to be capable of star for- mation, leaving the wounded gal- axy with fewer stellar nurseries in a dramatic transformation. But this galactic victim isn’t all that is being transformed. Balashev explains: “These mergers are thought to bring huge amounts of gas to supermas- sive black holes re- siding in galaxy centres.” In the cosmic joust, new reserves of fuel are brought within reach of the black hole powering the quasar. As the black hole feeds, the quasar can continue its dam- aging attack. This study was con- A stronomers have witnessed a violent galactic merger in deep space. Like a ‘cosmic joust’, one gal-axy is piercing another with a cone of intense radiation. The re- sults of their analysis, using both ESO’s Very Large Tele- scope (VLT) and the Atacama Large Millimeter/submil- limeter Array (ALMA), show that this radiation is disrupt- ing the gas and dust within the the other galaxy. [ESO] telescopes. The light from this ‘cos- mic joust’ has taken over 11 billion years to reach us, so we see it as it was when the Universe was only 18% of its current age. “Here we see for the first time the effect of a quasar’s radiation di- rectly on the internal structure of the gas in an otherwise regular gal- axy,” explains study co-lead Sergei Balashev, who is a researcher at the Ioffe Institute in St Petersburg, Rus- sia. The new observations indicate that radiation released by the quasar disrupts the clouds of gas and dust in the regular galaxy, leav- ing only the smallest, densest re- gions behind. These regions are likely !