UGC 1597, an irregular galaxy
from the SDSS
Most galaxies fit one of the three previously described types, but about 3% of the galaxies we observe are very different.
These so-called “irregular galaxies” do not have a lot of common features. Many of them are the results of galaxy collisions or near misses. One type of irregular galaxy is called a “starburst galaxy.” Starburst galaxies shine brightly as many new stars are born in a short period of time.
Irregular galaxies are usually found in groups or clusters, where collisions and near-misses between galaxies are common. In a few irregular galaxies, astronomers can’t figure out why they look so strange!
Irregular galaxies are denoted by the letters Irr.