In an extraordinary discovery, astronomers using NASA’s Chandra X-ray Observatory and other telescopes have found evidence that two galaxy clusters—huge groups of galaxies held together by gravity—are on course to collide for a second time.
This rare cosmic event is taking place about 2.8 billion light-years from Earth in a system called PSZ2 G181.06+48.47, or PSZ2 G181 for short.
Galaxy clusters are among the largest structures in the universe.
Each one can contain hundreds or even thousands of galaxies, vast clouds of superheated gas, and mysterious dark matter.
When two clusters collide, the event releases enormous energy and leaves behind traces that astronomers can detect, such as shock waves rippling through the gas.
The first collision between the clusters in PSZ2 G181 likely occurred around a billion years ago. At that time, powerful shock fronts—like the shock waves created by jets breaking the sound barrier—were formed.
These shock fronts, shaped like parentheses, were first spotted by a radio telescope network in the Netherlands called LOFAR (LOw Frequency ARray).
In new images, data from multiple telescopes have been combined: X-rays from Chandra and ESA’s XMM-Newton, radio signals from LOFAR, and visible light from the Pan-STARRS telescope.
The shock fronts from the original crash are still moving outward and are now separated by about 11 million light-years—the widest distance ever recorded between such structures. But the story doesn’t end there.
New observations show that the two galaxy clusters have slowed down, reversed direction, and are now heading back toward each other for a second, dramatic collision.
Scientists have also found three new shock fronts aligned with the path of the previous impact. These features are likely early signs that the second collision is on the way.
While astronomers are still working to calculate the exact masses of each cluster, they have already noted that this is one of the lighter systems known to undergo such a double collision, making it even more unusual.
The findings were published in The Astrophysical Journal in a series of three papers led by researchers from the Center for Astrophysics | Harvard & Smithsonian and Yonsei University in South Korea.
This rare chance to observe galaxy clusters crashing twice gives scientists an incredible opportunity to study how these giant structures interact, evolve, and shape the universe around them.
Source: KSR.
