NGC 4567 and NGC 4568 (nicknamed the Butterfly Galaxies or Siamese Twins ) are a set of unbarred spiral galaxies about 60 million light-years away in the constellation Virgo. They were both discovered by William Herschel in 1784. They are part of the Virgo Cluster of galaxies. These galaxies are in the process of colliding and merging with each other, as studies of their distributions of neutral and molecular hydrogen show, with the highest star-formation activity in the part where they overlap. However, the system is still in an early phase of interaction. In about 500 million years the galaxies will coalesce into a single elliptical galaxy. Four supernovae have been observed in the Butterfly Galaxies: SN 1990B (type Ib, mag. 16), SN 2004cc (type Ic, mag. 17.5), SN 2020fqv (type IIb, mag. 19), and SN 2023ijd (type II, mag. 16.8).

Naming controversy

The two galaxies were nicknamed "Siamese Twins" because they appear to be connected. On August 5, 2020, NASA announced that they would not use that nickname in an effort to avoid systemic discrimination in their terminology.