Throughout the history of the Universe, galaxies have been known for their epic dance-offs with each other, taking to the cosmic dance floor under gravity’s influence. They spin, fly and twirl as they get closer and closer to each other and eventually merge and grow into one big, mixed-up galaxy in a process known as a ‘galactic merger’. 

Recently, one pair of cosmic dancers has turned astronomer’s heads by performing a very dangerous routine — which they’ve nicknamed the cosmic joust! 

Two opposing galaxies play the role of knights, with one galaxy pointing a lance made of pure radiation right at the other! This radiation is super powerful, and it comes from an equally powerful source. 

At the centre of the galaxy is a hungry supermassive black hole, which swallows up lots of material around it and uses the extra energy to spit out intense light beams. This bright centre of the galaxy is called a quasar, and its radiation is so intense that it can damage anything it touches.

By watching the joust, astronomers got to see what happens when a galaxy finds itself on the wrong end of a quasar. The quasar’s radiation disrupts gas and dust inside the galaxy where it hits, tearing apart clouds of material. Only the smallest, densest regions of the galaxy make it through these battles, leaving the poor galaxy without much fuel for its stellar nurseries — the regions where new stars are born. Without as many new stars, the future of this galaxy doesn’t look very bright.

To study the effects of the quasar’s radiation on the other galaxy, the team used not just one, but two mighty telescopes — the European Southern Observatory’s Very Large Telescope (VLT), and the Atacama Large Millimeter/submillimeter Array (ALMA).

By studying the after-effects of massive events like galactic mergers or quasar blasts, astronomers can learn more about the long and complicated lives of galaxies. As telescopes get bigger and better, they’ll be able to search deeper into the cosmos to study scenarios like these. Perhaps they’ll even find more cosmic jousts — enough to make a whole tournament!

Image: This photo is an artist's impression of the cosmic joust, showing how the galaxy on the right hosts a quasar in the centre. It points this beam of intense radiation at the galaxy on the left, disrupting material within and carving out a gap in the gas and dust. Credits: ESO/M. Kornmesser