Two galaxy clusters 2.8 billion lightyears from Earth have collided and are on course to do so again, and astronomers have a front-row seat.
The two galaxy clusters, each containing hundreds or even thousands of galaxies, vast quantities of dark matter and superheated gas, are not only colliding, but are poised for a rematch.
More amazing Chandra observations
This encounter, involving galaxy cluster PSZ2 G181.06+48.47 (or PSZ2 G181), is one of the most dramatic events of its kind ever captured by scientists.
Observations using NASA’s Chandra X-ray Observatory, ESA’s XMM-Newton, the LOw Frequency ARray (LOFAR) and Pan-STARRS reveal stunning detail of the aftermath of the initial collision, and the early signs of an imminent second.
Shockwaves through the cosmos
A composite image created from this multi-observatory study shows crescent-shaped structures surrounding the system.
These, say the astronomers, are likely shock fronts: massive, sonic boom-like disturbances in the superheated gas between galaxies.
Similar to the wake of a supersonic jet, these shock fronts were likely formed by the high-speed impact caused when the clusters first collided about a billion years ago.
Now separated by 11 million lightyears, meaning a ray of light would take 11 million years to travel the distance between the two, these shock fronts are the largest ever seen from a galaxy cluster collision.
Yet despite their enormous distance, the galaxy clusters are gravitationally bound, and slowly turning back for another high-speed impact.
Second crash incoming...
Chandra and XMM-Newton’s X-ray vision has been crucial in revealing what's next for PSZ2 G181.
Astronomers identified three distinct shock fronts aligned with the direction of the clusters’ motion.
This alignment shows the two clusters, having slowed from their first encounter, are beginning to fall back toward one another, setting the stage for a second crash.
Lead author of the study Andra Stroe of the Center for Astrophysics | Harvard & Smithsonian says this second encounter offers scientists the chance to observe a lower-mass system undergoing the kind of large-scale violence typically seen in more massive clusters.
Key science takeaways
Galaxy cluster collisions are some of the most energetic events in the Universe.
They shape cosmic structures and can provide insights into the mysterious unseen substance known as dark matter, as well as galaxy evolution.
PSZ2 G181 is a lower-mass system compared to others that have undergone similar events, giving astronomers the chance to see how these collisions unfold under different conditions.
Read the full paper at iopscience.iop.org/article/10.3847/1538-4357/adb731
