Grad Student Discovers Shock Wave in Merging Galaxy Clusters, Confirms a Missing Link

Newswise — LEXINGTON, Ky. (June 16, 2022) — Arnab Sarkar, a graduate student in the University of Kentucky Department of Physics and Astronomy, will reveal data and images that — for the first time — confirm the existence of a shock wave created between two galaxy clusters early in the merging process.

The findings will be presented today during the American Astronomical Society’s (AAS) semiannual meeting, taking place in Pasadena, California this week.

Galaxy clusters are the most massive, gravitationally bound systems in the universe. When two galaxy clusters collide, theories predict that their first contact would create a shock wave between them. For the first time, Sarkar and his team detected such an axial shock between two clusters that are about to merge. 

Sarkar, who is also a predoctoral scholar with the Center of Astrophysics | Harvard & Smithsonian, says this is a very important confirmation in understanding the assembly of structures in the universe.

“With this discovery, we caught two sub-clusters of a galaxy cluster in a crucial early epoch of the merging process, with a strong shock between them, providing a missing link to the formation of the most massive structures in our universe,” he said.

The shock was detected using the Chandra X-Ray Observatory, in a galaxy cluster known as Abell 98, which lies more than 1,200 million light-years away from Earth. The strong shock wave Sarkar and his team detected travels at a speed of 4.5 million miles an hour between two sub-clusters, which is 20,000 times faster than the fastest Formula 1 cars.

Sarkar notes that catching galaxy clusters early in the merging process is very rare. Because they are millions of light years apart from each other. The axial shock waves predicted by the theory at the initial phase of their merger were never observed before. Detection of such a shock in an early- stage merging cluster was, therefore, a long-standing missing piece of the puzzle of galaxy cluster formation.

“This result is important because different computer simulations seem to be telling us different things about what we should observe early on in a galaxy cluster merger,” Sarkar said. “Here, we have a picture of what this process actually looks like, and that can be used to inform our theoretical models.”

Sarkar will present his findings at 10:15 a.m. PDT Thursday, June 16, during a briefing titled “Discovery of a Pre-merger Shock Wave in Abell 98: A Missing Piece in Building the Most Massive Structures in Our Universe.”

The study, “Discovery of a pre-merger shock in an intercluster filament in Abell 98,” has been submitted to the Astrophysical Journal Letters.

The press briefing may be watched live on AAS Press Office YouTube channel.

As the largest astronomy conference in the United States, the AAS meeting will bring together more than 2,000 astronomers, educators, students and journalists to highlight the nation’s most groundbreaking work in the fields of physics and astronomy.

The American Astronomical Society (AAS), established in 1899, is a major international organization of professional astronomers, astronomy educators and amateur astronomers. Its membership of approximately 8,000 also includes physicists, geologists, engineers and others whose interests lie within the broad spectrum of subjects now comprising the astronomical sciences. The mission of the AAS is to enhance and share humanity’s scientific understanding of the universe as a diverse and inclusive astronomical community, which it achieves through publishing, meetings, science advocacy, education and outreach, and training and professional development.

This material is based upon work supported by NASA under award number GO9-20112X. Any opinions, findings, and conclusions or recommendations expressed in this material are those of the author(s) and do not necessarily reflect the views of the National Aeronautics and Space Administration.