Astronomers observe in unprecedented detail a galactic collision at more than 3 million km per hour

The dramatic impact was observed in Stephan’s Quintet, a nearby galaxy group made up of five galaxies first spotted almost 150 years ago. The immensely powerful encounter was similar to the “sonic boom of a fighter jet,” one of the most astonishing phenomena in the universe.

The collision, announced this Friday in the magazine ‘Monthly Notices of the Royal Astronomical Society‘. was detected by a team of more than 60 astronomers using the first observations from the new €20 million Weave (William Herschel Telescope Enhanced Area Velocity Explorer) wide-field spectrograph.

“Since its discovery in 1877, the Stephan Quintet has captivated astronomers because it represents a galactic crossroads where past collisions between galaxies have left behind a complex debris field,” said lead researcher Marina Arnaudova of the University of Hertfordshire.

“Dynamic activity in this group of galaxies has been reawakened by a galaxy crashing into it at an incredible speed of more than 3.2 million km/h, causing an immensely powerful shock, much like the sonic boom.” of a fighter plane,” he summarizes.

Supersonic speeds

The international team has discovered a dual nature behind the shock front, previously unknown to astronomers. “As the shock wave moves through pockets of cold gas, it travels at hypersonic speeds (several times the speed of sound in the intergalactic medium of Stephan’s Quintet), powerful enough to separate electrons from atoms, leaving behind a bright trail of charged gas, as seen with Weave,” he noted. Arnaudova.

However, when the shock wave passes through the surrounding hot gas, it becomes much weaker, according to PhD student Soumyadeep Das, from the University of Hertfordshire. “Rather than causing a significant disturbance, the weak shock compresses the hot gas, producing radio waves that are captured by radio telescopes such as the Low Frequency Array (LOFAR),” he added.

For Gavin Dalton, principal investigator of Weave at the University of Oxford, “it is fantastic to see the level of detail discovered.” In his opinion, “in addition to the details of the crash and the unfolding collision that we see in Stephan’s Quintet, these observations provide remarkable insight into what may be happening in the formation and evolution of the weak, barely resolved galaxies that we see in the limits of our current capabilities.

“I’m excited to see the data collected in Weave’s first light already provide a high-impact result, and I’m confident that this is just an early example of the types of discoveries that will be possible with Weave on the William Herschel Telescope in the coming years,” said Marc Balcells, director of the Isaac Newton Telescope Group.