Hoag's Object

Hoag's Object is an unusual ring galaxy. Though it can be classified by appearance as a ring galaxy, it defies the common theories of ring-galaxy formation, suggesting it is different kind of object and its formation remains a topic of interest. The object was discovered in 1950 by Arthur Hoag, who initially theorized it to be either an odd galaxy or a planetary nebula. It is positioned so we have a face-on view of the ring. Hoag himself also considered it could result from gravitational lensing, i.e., an Einstein ring, which is now discounted, given redshift measurements of the center compared with those of the ring.