Cartwheel Galaxy
The Cartwheel Galaxy is a lenticular galaxy and ring galaxy about 500 million light-years away in the constellation Sculptor. It is a D₂₅ isophotal diameter of 44.23 kiloparsecs, and has a mass of about 2.9–4.8 × 10⁹ solar masses; its outer ring has a circular velocity of 217 km/s. It was discovered by Fritz Zwicky in 1941. Zwicky considered his discovery to be "one of the most complicated structures awaiting its explanation on the basis of stellar dynamics." An estimation of the galaxy's span resulted in a conclusion of 150,000 light years, which is slightly smaller than the Andromeda Galaxy. The Third Reference Catalogue of Bright Galaxies measured a D₂₅ isophotal diameter for the Cartwheel Galaxy to be about 60.9 arcseconds, which gives it a diameter of 44.23 kiloparsecs based on a redshift-derived distance of 132.2 megaparsecs. The large Cartwheel galaxy is the dominant member of the Cartwheel galaxy group, which consists of four physically associated spiral galaxies.
