(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
and Hoag also considered gravitational lensing,
i.e., an Einstein ring,
which redshift measurements of the center and ring discount.
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