Hubble image of Arp 224, also known as NGC 3921.
NGC 3921 is a pair of interacting disk galaxies that are in the late stages of a merger. The history of this merger is recorded in the tails and loops that surround the center.
The galaxies were about the same mass and likely collided about 700 million years ago.
Credit: ESA, NASA, J. Schmidt
Source: https://esahubble.org/images/potw1537a/