Galaxy collision at 2M MPH seen

A massive collision of galaxies, triggered by one traveling at an astonishing 2 million mph (3.2 million km/h), has been observed in unprecedented detail by one of Earth’s most powerful telescopes.

The dramatic impact occurred in Stephan's Quintet, a nearby galaxy group consisting of five galaxies, first discovered nearly 150 years ago. The collision ignited an immensely powerful shockwave, likened to a “sonic boom from a jet fighter,” one of the most striking phenomena in the Universe.

Photo credit: University of Hertfordshire

Massive galaxy collision at 2M MPH seen in unprecedented detail

Stephan's Quintet is considered a 'galactic crossroads,' where past collisions have left behind a complex field of debris. This field has now been reawakened by the passage of the galaxy NGC 7318b.

The collision was observed by a team of scientists using the new 20-million Euro (£16.7 million) William Herschel Telescope Enhanced Area Velocity Explorer (WEAVE) wide-field spectrograph, located in La Palma, Spain. This cutting-edge science facility is set to not only reveal the formation of the Milky Way but also provide insights into millions of galaxies across the Universe.

The discovery, documenting NGC 7318b's collision with Stephan's Quintet, was made by a team of more than 60 astronomers. The findings have been published in Monthly Notices of the Royal Astronomical Society. The system serves as an ideal laboratory for understanding the chaotic and violent relationships between galaxies, which is why it was the focus of WEAVE’s first-light observation using its Large Integral Field Unit (LIFU).

Lead researcher Dr. Marina Arnaudova from the University of Hertfordshire commented, “Since its discovery in 1877, Stephan's Quintet has fascinated astronomers because it represents a galactic crossroads, where past collisions have created a complex field of debris. Now, this dynamic activity has been reignited by a galaxy smashing through it at an incredible speed of over 2 million mph, causing a powerful shock similar to a sonic boom from a jet fighter.”

The international team uncovered a dual nature behind the shock front, previously unknown to astronomers. As the shock 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 strip electrons from atoms, leaving behind a glowing trail of charged gas. This phenomenon was captured by WEAVE.

However, when the shock moves through surrounding hot gas, it weakens, with the shock compressing the hot gas and generating radio waves, detected by radio telescopes like the Low Frequency Array (LOFAR), according to PhD student Soumyadeep Das from the University of Hertfordshire.

The WEAVE prime-focus corrector and positioner at the William Herschel telescope in La Palma, Spain

The new insights came from WEAVE’s LIFU, combining data from other advanced instruments such as LOFAR, the Very Large Array (VLA), and the James Webb Space Telescope (JWST).

Photo credit: University of Hertfordshire

WEAVE, a state-of-the-art super-fast mapping device, is connected to the William Herschel Telescope to analyze the composition of stars and gas within the Milky Way and in distant galaxies. It utilizes a spectroscope to reveal the elements stars are made of by generating a barcode-like pattern within a prism of colors from a light source.

WEAVE was designed and built through a multi-lateral agreement among France, Italy, and the countries of the Isaac Newton Group of Telescopes (the UK, Spain, and the Netherlands).

Astronomers hope that WEAVE will revolutionize the understanding of galaxy formation and offer unprecedented insights into the Universe.

Dr. Daniel Smith from the University of Hertfordshire stated, "It’s remarkable work by Marina and her large team, but this first WEAVE science paper represents just the beginning of what’s to come as WEAVE becomes fully operational."

Professor Gavin Dalton, WEAVE principal investigator at RAL Space and the University of Oxford, added, "It's fantastic to see the level of detail uncovered by WEAVE. These observations not only provide insights into the shock and unfolding collision in Stephan's Quintet but also offer a rare perspective on the formation and evolution of faint galaxies beyond current capabilities."

Dr. Marc Balcells, director of the Isaac Newton Group of Telescopes, concluded, “The data gathered at WEAVE’s first light already provide a high-impact result, and this is just an early example of the discoveries WEAVE will enable in the coming years.”

WEAVE decomposition of gas in Stephan's Quintet

Photo credit: University of Hertfordshire