When a small galaxy cluster disturbs a larger one, giant waves emanate for millions of years.
Billions of years ago, a small galaxy made a flyby of the massive Perseus galaxy cluster. The flyby made a gravitational disturbance that caused a cosmic shock wave, which generated ripples of hot gas in Perseus roughly twice the size of our own Milky Way. NASA’s Chandra X-ray Observatory provided researchers with extremely detailed images of Perseus, which they compared to a computer simulation to better understand the initial disturbance. One feature they observed was a mysterious, curved feature known as the "bay.” According to the simulation, the smaller galaxy's flyby mixed the layers of hot and cool gas within Perseus. This caused the cooler gas to spiral outwards, producing giant waves that persist for hundreds of millions of years and forming the bay, whose “shore” is a profile view of the wave itself. Scientists were able to make extremely difficult measurements that clarified the relationship between the size of the waves and the strength of the cluster's magnetic field. Watch the video to see the giant ripples in action.