Tour: Galaxy Cluster Relaxed Now, but was Wild in the Past
(Credit: NASA/CXC/A. Hobart)
[Runtime: 02:34]

With closed-captions (at YouTube)

The galaxy cluster Abell 2029 has sometimes been described as “the most relaxed cluster in the Universe.” This moniker does not arise from some sort of mellow vibe, but rather because of how calm and undisturbed the superheated gas that pervades the cluster appeared to be.

Now, new observations from NASA’s Chandra X-ray Observatory clearly show that Abell 2029 had a much more colorful history than its current disposition suggests. The latest study finds that Abell 2029 is still settling down after a raucous collision with another smaller cluster about four billion years ago.

Galaxy clusters are the largest structures in the Universe held together by gravity. They are made up of hundreds or even thousands of galaxies, dark matter detected only by its gravitational effects, and a huge amount of gas that fills in the space between the galaxies. This gas is typically heated to millions of degrees, which makes it glow in X-ray light.

The Chandra data reveal clear signs that this cluster did not have a mundane history. Evidence for the cluster’s previous shenanigans comes from the nautilus-like shape in the Chandra data. A team of researchers who analyzed the data think the spiral shape in the hot gas formed when gas in the cluster sloshed to the side because of the gravitational effects of the cluster collision — similar to how wine moves in a wine glass. The sloshing spiral in Abell 2029 is one of the longest ever seen, extending about two million light-years from the center of the cluster.

Computer simulations of the collision suggest that the smaller cluster was about ten times less massive than the larger cluster. The sloshing spiral formed when the smaller cluster made its first pass through the larger cluster, pulling its gas sideways. The gravity of the larger cluster then caused the other cluster to slow down and get pulled back in for a second collision. This drove a shock front and left behind a wake of material, forming the splash region.

Quick Look: Galaxy Cluster Relaxed Now, but was Wild in the Past
(Credit: NASA/CXC/A. Hobart)
[Runtime: 00:46]

With narration (video above with voiceover)

The Abell 2029 galaxy cluster appears calm now but apparently had a wild past.

This discovery was made using data from NASA’s Chandra X-ray Observatory.

A nautilus-like structure in the X-ray data is evidence for a collision 4 billion years ago.

The collision caused the gas to slosh around the cluster like wine in a glass.