A long time ago gravity drew the two galaxies together into the chaotic state we now observe. Stars from within both of the original galaxies now follow new trajectories caused by the new gravitational effects. However, actual collisions between stars themselves are very rare as stars are very small relative to the distances between them (most of a galaxy is empty space). Eventually things will settle down and one day the two galaxies will have fully merged to form a single, stable galaxy. Our own galaxy, the Milky Way, will undergo a similar collision in the future with our nearest galactic neighbor, the Andromeda Galaxy. Although this is not expected to happen for around 4 billion years so there is nothing to worry about just yet. This object was previously observed by Hubble with its old WFPC2 camera. That image was released in 2015.
