Tour: Galaxy Clusters on Course to Crash Again, NASA's Chandra Finds

New observations from NASA’s Chandra X-ray Observatory and other telescopes have captured a powerful cosmic event: two galaxy clusters have collided and are now poised to head back for another swipe at each other.

Galaxy clusters are some of the largest structures in the Universe. Held together by gravity, they are monster-sized collections of hundreds or thousands of individual galaxies, massive amounts of superheated gas, and invisible dark matter.

The galaxy cluster — known as PSZ2 G181 for short — is about 2.8 billion light-years from Earth. Previously, radio observations from the LOw Frequency Array, or LOFAR, spotted parentheses-shaped structures on the outside of the system. LOFAR is an antenna network of radio telescopes in the Netherlands.

These structures are probably shock fronts — similar to those created by jets that have broken the sound barrier — likely caused by disruption of gas from the initial collision about a billion years ago. Since the collision they have continued traveling outwards and are currently separated by about 11 million light-years, the largest separation of these kinds of structures that astronomers have ever seen.

Now, data from NASA’s Chandra and ESA’s XMM-Newton is providing evidence that PSZ2 G181 is poised for another collision. Having a first pass at ramming each other, the two clusters have slowed down and begun heading back toward a second crash.

Astronomers want to study galaxy cluster collisions because they are an important way that these giant structures grow and evolve, helping them better understand how the Universe changes over cosmic time.