This beautiful but very small object's structure can only be appreciated in images like the Hubble.  I thought it would be interesting to process this using the techniques I use for planetary nebulae to see if I could pick up some of the unusual ring structure now that I have clean sky at SRO..  So here is the object in the original L image then processed with BlurX, NoiseX and GHS.  You can then discern the double ring structure.  If I did not have the Hubble and Wikipedia image, might have guessed it was an artifact.

Wikipedia:  Hoag's Object is an unusual ring galaxy in the constellation of Serpens Caput.[4]  It is named after Arthur Hoag who discovered it in 1950 and identified it as either a planetary nebula or a peculiar galaxy.[5]  The galaxy has approximately eight billion stars, and is roughly 120,000 light years across.[6]  A nearly perfect ring of young hot blue stars circles the older yellow nucleus of this ring galaxy c. 600 million light-years away in the constellation Serpens.

The ring structure is so perfect and circular that it has been referred to as "The most perfect ring galaxy".[7]  The diameter of the 6 Arc" inner core of the galaxy is about 17±0.7 kly (5.3±0.2 kpc) while the surrounding ring has an inner 28 Arc″ diameter of 75±3 kly (24.8±1.1 kpc) and an outer 45 Arc″ diameter of 121±4 kly (39.9±1.7 kpc).[2]  The galaxy is estimated to have a mass of 700 billion suns.[8]  By comparison, the Milky Way galaxy has an estimated diameter of 150-200 kly and consists of between 100 and 500 billion stars and a mass between 800 billion and 1.54 trillion suns.[9][10]  The gap separating the two stellar populations may contain some star clusters that are almost too faint to see.

Though ring galaxies are rare, another more distant ring galaxy (SDSS J151713.93+213516.8)[11] can be seen through Hoag's Object, between the nucleus and the outer ring of the galaxy, at roughly the one o'clock position in the image shown here.  Noah Brosch and colleagues showed that the luminous ring lies at the inner edge of a much larger neutral hydrogen ring.[7]