Two-million-miles-per-hour galaxy collision seen in detail

The impact was observed in Stephan’s Quintet, a nearby galaxy group made up of five galaxies.

Radio observations of Stephan’s Quintet at different frequencies (University of Hertfordshire)

A massive collision of galaxies sparked by one travelling at two million miles per hour (mph) has been seen in unprecedented detail by one of Earth’s most powerful telescopes.

The impact sparked an immensely powerful shock similar to a sonic boom from a jet fighter – the likes of which are among the most striking phenomena in the Universe, experts suggest.

It was observed in Stephan’s Quintet, a nearby galaxy group made up of five galaxies first sighted almost 150 years ago.

An image revealing the age of high-energy plasma in Stephan's Quintet, as captured by radio observations with the VLA and LOFAR — The blue colours indicate older, low-energy plasma, while the orange and yellow areas mark regions that are being actively energised (M. Arnaudova/University of Hertfordshire/WEAVE consortium/PA)

A team of scientists led by the University of Hertfordshire captured the event using the new 20 million euro William Herschel Telescope Enhanced Area Velocity Explorer (Weave) wide-field spectrograph in La Palma, Spain.

Dr Marina Arnaudova said: “Since its discovery in 1877, Stephan’s Quintet has captivated astronomers, because it represents a galactic crossroad where past collisions between galaxies have left behind a complex field of debris.

“Dynamical activity in this galaxy group has now been reawakened by a galaxy smashing through it at an incredible speed of over two million miles per hour, leading to an immensely powerful shock, much like a sonic boom from a jet fighter.”

Weave data overlaid on a James Webb Space Telescope image of Stephan’s Quintet, with green contours showing radio data from the Low Frequency Array radio telescope (M. Arnaudova/University of Hertfordshire/WEAVE consortium)

The researchers uncovered a dual nature behind the shock front, previously unknown to astronomers.

They found that as the shock moves through pockets of cold gas, it travels at hypersonic speeds, powerful enough to rip apart electrons from atoms, leaving behind a glowing trail of charged gas.

However, when the shock passes through the surrounding hot gas, it becomes much weaker, according to PhD student Soumyadeep Das, of the University of Hertfordshire.

WEAVE decomposition of gas in Stephan's Quintet, overlaid on a JWST image — The red highlights gas shocked by the collision, while green and blue shows star-forming regions (M. Arnaudova/University of Hertfordshire/WEAVE consortium)

He added: “Instead of causing significant disruption, the weak shock compresses the hot gas, resulting in radio waves that are picked up by radio telescopes like the Low Frequency Array (LOFAR).”

The new insight and unprecedented detail came from Weave, combining data with other cutting-edge instruments, and the James Webb Space Telescope (JWST).

The findings are published in the Monthly Notices of the Royal Astronomical Society journal, and researchers believe that Weave is set to revolutionise our understanding of the Universe.