Observations by the Chandra X-ray Observatory and other telescopes have recorded a rare cosmic phenomenon: two previously collided clusters of galaxies are preparing to collide again.
Galactic clusters are some of the largest structures in the Universe. Held together by gravity, they are giant clusters containing hundreds or thousands of individual galaxies, vast amounts of superheated gas, and invisible dark matter.
One such cluster is PSZ2 G181.06+48.47 (abbreviated PSZ2 G181), located 2.8 billion light-years from Earth. Earlier radio astronomical observations made with the LOFAR (LOw Frequency ARray) antenna network recorded bracket-shaped structures on the outside of the system. They are shock fronts – similar to those created by jets breaking the sound barrier.
The shock waves are most likely evidence of a collision between two separate galactic groups that happened about a billion years ago. After the impact, they continued to move outward and are currently separated by a distance of about 11 million light-years. This is the largest distance between structures of this kind that astronomers have ever observed.
However, this is not yet the most interesting part. Data obtained by ESA’s Chandra and XMM-Newton telescopes proved that the clusters composing PSZ2 G181 are preparing for a “second round”. After the first collision, they slowed down and began their return. Astronomers made detailed X-ray observations and detected three shock fronts. They are aligned on the axis of impact. Researchers believe these are early signs of an impending second collision.
Astronomers are still trying to determine how much mass each colliding cluster contains. But regardless, their total mass is less than that of other systems in which galaxy clusters have collided. This makes PSZ2 G181 a very rare and interesting object to study.
Earlier, we told you about how Chandra discovered a “fracture” in the Milky Way.
Provided by Chandra.si.edu
