(peculiar ring galaxy)
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.
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