The galaxy was a normal spiral galaxy before it had a collision with a smaller galaxy about 200 million years ago. When the nearby galaxy passed through the Cartwheel Galaxy, the power of the collision sent a strong shock wave through the galaxy. Moving at high speed, the shock wave moved gas and dust. This made a starburst around the galaxy's center. This explains the blue colored ring around the center, bright section. It can be seen that the galaxy is beginning to take the shape of a normal spiral galaxy again. Spiral arms are spreading out from a central core.
There are other possible explanations of the ring-like appearance.
- Moore, Patrick 2000. The data book of Astronomy. CRC Press, 318. ISBN 0-7503-0620-3
- "Amazing Space - fast facts: Cartwheel Galaxy". Amazing Space. 2008. Retrieved 2009-07-03.
- Amram P.; et al. (1998). "The Hα kinematic of the Cartwheel galaxy". Astron Astrophys. 330: 881–93. Bibcode:1998A&A...330..881A.
- Zwicky F (1941). Theodore van Karman Anniversary volume: contribution to applied mechanics and related subjects. Pasadena, California: California Institute of Technology. p. 137.
- Griv E (2005). "Origin of the Cartwheel Galaxy: disk instability?". Astrophys Space Sci. 299 (4): 371–85. Bibcode:2005Ap&SS.299..371G. doi:10.1007/s10509-005-3423-5.
- Mayya YD; et al. (2005). "The discovery of spiral arms in the starburst galaxy M82". Ap J. 628 (1): L33. arXiv:astro-ph/0506275. Bibcode:2005ApJ...628L..33M. doi:10.1086/432644.
- That is, 200 million years before the image. We see the galaxy as it was 500 million years ago, and the collision took place 700 million years ago.
- "Cartwheel Galaxy". College of Southern Nevada. Retrieved 2009-07-03.
- Platt, Jane (2006). "Cartwheel galaxy makes waves in new NASA image". NASA. Retrieved 2009-05-15.