Stephan's Quintet, a group of five galaxies discovered nearly 150 years ago, is a cosmic meeting point where past galactic collisions have left a debris-filled environment. The recent event, driven by the passage of the galaxy NGC 7318b, triggered a shockwave described as similar to "a sonic boom from a jet fighter."

The discovery, made using the William Herschel Telescope's new WEAVE wide-field spectrograph in La Palma, Spain, has provided extraordinary insights into the dynamics of galactic collisions. This euro 20 million ( Pounds 16.7 million) instrument is expected to reveal details about the Milky Way's formation and the broader universe over billions of years.

Dr. Marina Arnaudova of the University of Hertfordshire, the lead researcher, remarked: "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 2 million mph (3.2 million km/h), leading to an immensely powerful shock, much like a sonic boom from a jet fighter."

The collision's shockwave, moving at hypersonic speeds, ionizes cold gas by stripping electrons from atoms and leaving behind a luminous trail of charged gas. "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 rip apart electrons from atoms, leaving behind a glowing trail of charged gas, as seen with WEAVE," added Dr. Arnaudova.

In contrast, as the shock encounters hot gas, it weakens significantly. Soumyadeep Das, a PhD student at the University of Hertfordshire, explained: "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)."

This discovery was made possible by combining WEAVE data with information from other advanced instruments, including the LOFAR, the Very Large Array (VLA), and the James Webb Space Telescope (JWST). WEAVE uses spectroscopic analysis to study the elemental composition of stars and gas, revealing the light "bar codes" of celestial objects with unparalleled precision.

Built through a collaboration involving France, Italy, and members of the Isaac Newton Group of Telescopes (the UK, Spain, and the Netherlands), WEAVE promises to revolutionize the study of galaxy formation and evolution.

Dr. Daniel Smith of the University of Hertfordshire commented: "It's really neat work that Marina has put together with this large team, but this first WEAVE science paper also represents just a taste of what is to come over the next five years now that WEAVE is becoming 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 here by WEAVE. As well as the details of the shock and the unfolding collision that we see in Stephan's Quintet, these observations provide a remarkable perspective on what may be happening in the formation and evolution of the barely resolved faint galaxies that we see at the limits of our current capabilities."

Dr. Marc Balcells, director of the Isaac Newton Group of Telescopes, expressed optimism about the instrument's future contributions: "I'm excited to see that the data gathered at the WEAVE first light already provide a high-impact result, and I'm sure this is just an early example of the types of discoveries that will be made possible with WEAVE on the William Herschel Telescope in the coming years."

Related Links
Royal Astronomical Society
Stellar Chemistry, The Universe And All Within It