A galaxy traveling at a blistering two million miles per hour (3.2 million km/h) has torn through five neighboring galaxies, creating one of the most powerful intergalactic shock waves ever observed.
The intense event unfolded in Stephan’s Quintet, a galactic cluster initially identified nearly a century and a half ago. The collision was documented and published in the Monthly Notices of the Royal Astronomical Society by an international team at the William Herschel Telescope Enhanced Area Velocity Explorer (WEAVE) wide-field spectrograph in La Palma, Spain.
This collision triggered by the galaxy NGC 7318b has fundamentally altered Quintet’s dynamics. The galaxy’s violent passage through the group has illuminated new aspects of galactic interactions and provided an unprecedented glimpse into the chaotic processes that govern the universe.
Galactic Shock Waves and Plasma Trails
Stephan’s Quintet, located in the constellation Pegasus about 290 million light-years from Earth, has long captivated astronomers. It represents a laboratory for studying how galaxies interact, merge, and evolve. The Quintet is an area where cosmic-grade gravitational forces clash, resulting in debris remnants, the birth of new stars, and intricate flows of ionized gas.
Marina Arnaudova, the lead researcher from the University of Hertfordshire, described Stephan’s Quintet as “a galactic crossroads” where past collisions and mergers have shaped its structure.
“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.”
This recent upheaval shows just how violent the universe can be. The crash unleashed a colossal shock wave—similar to the roar of a supersonic jet magnified to an extraordinary degree. This wave possessed the strength to strip electrons from atoms, resulting in luminous plasma trails astronomers can chart with WEAVE.
The shock wave ended up exhibiting a dual nature.
One of the study’s key findings was the behavior of the shock wave as it moved through different types of gas. In regions of cold gas, the shock travels at hypersonic speeds, tearing apart atomic structures and leaving behind luminous ribbons of charged particles. These regions glow brightly in hydrogen-alpha light, observed using WEAVE’s Large Integral Field Unit.
However, as the shock wave penetrates regions of heated gas, its behavior changes significantly.
“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,” Arnaudova said.
This discovery has opened new avenues to study how galaxy collisions distribute energy and matter over enormous scales, offering insights into how similar processes might unfold in more distant, less accessible systems.
“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,” said Gavin Dalton, WEAVE principal investigator at RAL Space and the University of Oxford.
