NGC 7331

NGC 7331 (also known as Caldwell 30) is a spiral galaxy about 40 million light-years (12 Mpc) away in the constellation Pegasus. It was discovered by William Herschel in 1784. NGC 7331 is the brightest member of the NGC 7331 Group of galaxies.

The galaxy is similar in size and structure to the galaxy we inhabit, and is often referred to as "the Milky Way's twin", although recent discoveries regarding the structure of the Milky Way may call this similarity into doubt.

Retrograde bulge

In spiral galaxies the central bulge typically co-rotates with the disk but the bulge in the galaxy NGC 7331 is rotating in the opposite direction to the rest of the disk. The current bulge may have formed from infalling material, however if it has been there since the formation of the galaxy then it would be difficult to explain how such a situation arose.

Supernova

SN 1959D, a Type IIL supernova, is the only supernova that has been identified within NGC 7331. The supernova was discovered by Milton Humason and H. S. Gates in a survey at Palomar Observatory.