List of ring galaxies
Name Catalogue number Distance Notes
Cartwheel Galaxy ESO 350-40 , PGC 2248 500 Mly lenticular galaxy
NGC 6028 NGC 6028 , NGC 6046 , PGC 56716 203 Mly barred lenticular galaxy
Hoag 's Object PGC 54559 , PRC D-51 600 Mly
SDSS J151713.93+213516.8 This galaxy can be seen behind Hoag 's Object
AM 0644-741 AM 0644-741 300 Mly
NGC 1291 NGC 1291 , NGC 1269 , PGC 012209 33 Mly
NGC 1512 PGC 14391 38 Mly Galaxy exhibits a double-ring structure
NGC 1533 NGC 1533 , PGC 14582 62 ± 4 Mly
NGC 2859 UGC 5001 , PGC 26649 82.8 Mly lenticular galaxy with ring structure
NGC 1350 PGC 013059 87.4 Mly spiral galaxy with ring structure
NGC 4622 PGC 42701 200 Mly unbarred spiral galaxy with ring
NGC 4777 NGC 4777 , PGC 43852
NGC 7217 UGC 11914 , PGC 68096 50 Mly unbarred spiral galaxy with ring
II Zw 28 Zw II 28 , 2MASX J05014205+0334278
Mayall 's Object Arp 148 , VV 032 , MCG+07-23-019 , APG 148 450 Mly collisional ring galaxy
I Zw 045 I Zw 045 , NGC 4774 collisional ring galaxy
VII Zw 466 VII Zw 466 , UGC 07683 collisional ring galaxy
Arp 10 Arp 10 , UGC 01775 , 2MASX J02182639+0539139 collisional ring galaxy
Arp 147 IC 298 interacting pair
NGC 4650A PGC 42951 polar ring galaxy
List
This is a list of ring galaxies. A ring galaxy, as the name suggests, is a disc or spiral galaxy with its galactic disc structured or distorted into a ring or torus-like appearance. Hoag's Object, discovered by Art Hoag in 1950, is the prototypical example of a ring galaxy. Ring galaxies are theorized to be formed through multiple possible situations- 
1. Bar instability - a phenomenon where the rotational velocity of the bar in a barred spiral galaxy increases to the point of spiral spin-out. Under typical conditions, gravitational density waves would favor the creation of spiral arms. When bar instability occurs, these density waves are instead migrated out into a ring-structure by the pressure, force, and gravitational influence of the byronic and dark matter furiously orbiting about the bar. This migration forces the stars, gas and dust found within the former arms into a torus-like region, forming a ring, and often igniting star formation. 2. Galactic collisions- another observed way that ring galaxies can form is through the process of two or more galaxies colliding. The cartwheel galaxy, galaxy pair AM 2026-424, and Arp 147 are all examples of ring galaxies believed to be formed from this process. In pass-through galactic collisions, an often smaller galaxy will pass through the disc of an often larger spiral, causing an outward push of the arms, as if dropping a rock into a pond of still water.