NGC 4567 and NGC 4568 Butterfly Galaxies
NGC 4567 and NGC 4568, nicknamed the Butterfly Galaxies or the Siamese Twins, are a pair of unbarred spiral galaxies located in the constellation Virgo and are members of the Virgo Cluster of galaxies. Discovered by William Herschel in 1784, the pair lies roughly 60 million light-years away and is caught in the early stages of a slow collision and merger, with their centers separated by only about 20,000 light-years.
Studies of the galaxies' neutral and molecular hydrogen show the highest rate of star formation occurring where the two disks overlap, though their overall spiral structures remain largely intact at this early stage of interaction. Over the next several hundred million years, gravitational forces are expected to draw NGC 4567 and NGC 4568 together until they coalesce into a single elliptical galaxy.
Another galaxy, NGC 4564, is visible in the image at the top right. It is an eliptical galaxy about 57 million light-years distant.