NGC 520 is a pair of colliding spiral galaxies about 105 million light-years away in the constellationPisces. They were discovered by astronomer William Herschel on 13 December 1784.

Halton Arp called this the second-brightest very disturbed galaxy in the sky, and it is as bright in the infrared and radio bands as the Antennae Galaxies. Simulations indicate this object consists of two galactic disks that began interacting about 300 million years ago. The system is still in an early stage of its merger, showing two separate velocity systems in the spectra, and two small tails. Two galactic nuclei have been detected, and one is an H II nucleus.