The Antennae Galaxies.

Image Credit: NASA, ESA, and the Hubble Heritage Team (STScI/AURA)-ESA/Hubble Collaboration

Two spiral galaxies, drawn together by gravity, started to interact a few hundred million years ago. The Antennae Galaxies are the nearest and youngest examples of a pair of colliding galaxies. They are currently going through a starburst phase, in which the collision of clouds of gas and dust, with entangled magnetic fields, causes rapid star formation.

Source: NASA