Astronomers have observed a cosmic collision traveling at 3.2 million km/h (2 million mph). Using a new instrument, they have detected a galaxy speeding through a group of others, creating a shock wave that is transforming the entire region.
Stephan’s Quintet consists of five galaxies closely located in the sky, initially discovered by French astronomer Édouard Stephan in 1877. Despite its serene name and appearance, this structure is witnessing a slow-motion collision.
The collision in Stephan’s Quintet resembles glass and metal scattered on a road after a car crash. Four galaxies have already collided, flinging their material into a debris field, and are gradually merging back together to form a single giant galaxy.
Despite the galaxies traveling at incredible speeds, the merger process will take several million years to complete on a cosmic scale. From our perspective, it appears frozen in time.
Interestingly, although it’s called a quintet, only four galaxies are involved in the collision. The lighter galaxy in the upper-left corner of the image is actually more than 200 million light-years closer to Earth than the rest of the group. It is merely photobombing the scene, unbeknownst to Stephan in the 19th century.
Recent observations with advanced instruments have provided more insight into the collision. Contrary to appearances, this moment in time is not tranquil, as one galaxy is actively colliding with the others.
The discovery was made with WEAVE, a new spectrograph attached to the William Herschel Telescope in Spain, in collaboration with LOFAR, James Webb, and the Very Large Array. Over 60 astronomers from different countries measured the impact on the system.
The main galaxy responsible for the collision is NGC 7318b, visible as the bright upper spot in the center of the image. This galaxy is approaching the group from behind, appearing to head straight towards us from Earth’s perspective.
The team determined that NGC 7318b is moving at an astonishing speed of over 3.2 million km/h (2 million mph), generating a strong shock wave in the neighboring galaxies. This shock wave exhibits different characteristics as it moves through various types of gas regions.
“As the shock advances through cold gas pockets, it travels at hypersonic speeds – several times faster than sound in Stephan’s Quintet’s intergalactic medium – causing electrons to separate from atoms, leaving a trail of charged gas seen with WEAVE,” explained Dr. Marina Arnaudova, the lead researcher.
The team anticipates that these findings will enhance our understanding of galaxy dynamics, formation, and evolution over time. This successful experiment marks WEAVE’s inaugural operation, promising further significant insights in the future.
The study was published in the Monthly Notices of the Royal Astronomical Society.
Source: Royal Astronomical Society
