A giant galaxy cluster once thought to be one of the calmest places in the universe is now revealing signs of a violent past.
Astronomers studying the galaxy cluster Abell 2029 have discovered evidence that it collided with a smaller cluster billions of years ago.
Although the cluster looks peaceful today, new observations show that the enormous crash left behind swirling gas, shock waves, and other dramatic structures that are still visible after roughly 4 billion years.
The research is based on the deepest X-ray observations ever taken of Abell 2029 using NASA’s Chandra X-ray Observatory.
The study was led by scientists from Boston University and the Center for Astrophysics | Harvard & Smithsonian.
Galaxy clusters are the largest structures in the universe held together by gravity. They contain hundreds or even thousands of galaxies, along with huge amounts of dark matter and extremely hot gas. This gas reaches temperatures of millions of degrees and glows brightly in X-rays.
For years, Abell 2029 was considered unusually “relaxed” because its hot gas appeared smooth and undisturbed. But the new Chandra observations tell a very different story.
The scientists found a giant spiral-shaped structure hidden inside the hot gas. The spiral stretches about two million light-years across, making it one of the largest sloshing spirals ever seen in a galaxy cluster.
Researchers believe this structure formed when a smaller galaxy cluster crashed through Abell 2029 long ago. The collision disturbed the hot gas and caused it to slosh back and forth, similar to wine swirling around inside a glass after it is shaken.
The team also discovered several other features linked to the ancient collision. One is a huge splash-like region of cooler gas that may have formed as material was thrown outward during the impact. Another possible feature is a shock wave moving through the hot gas, similar to the sonic boom created by a supersonic aircraft.
The researchers also identified a mysterious structure called a “bay.” They think this may have formed where the outer edge of the spiral overlaps with gas stripped away from the smaller cluster during the collision.
Computer simulations suggest the smaller cluster was about ten times less massive than Abell 2029. According to the simulations, the smaller cluster first passed through the larger one, pulling its gas sideways with gravity. It later slowed down and fell back toward the larger cluster again, creating additional disturbances and shock waves.
To reveal these hidden structures, the researchers used a special imaging technique. Most of the cluster’s hot gas forms a smooth oval shape. By digitally removing this smooth background from the X-ray images, the unusual features became much easier to see.
The discovery helps astronomers better understand how galaxy clusters grow and evolve over billions of years. It also shows that even the most peaceful-looking regions of the universe may hide evidence of ancient cosmic violence.
Source: KSR.
