Spiral Galaxy
Type of galaxy in the Hubble sequence which is characterized by the following physical properties:
NGC 628 (also known as M74) presents a face-on view of its spiral arms. It contains about 100 billion stars, 30 million light-years away toward the constellation Pisces.
- A considerable total angular momentum
- Composed of a central bulge surrounded by a disk
- The bulge resembles an elliptical galaxy, containing many old, so-called "Population II" stars, and usually a supermassive black hole at its center.
- The disk is a flat, rotating assembly consisitng of interstellar matter, young "Population" stars and open star clusters.
The disks of spiral galaxies tend to be surrounded by large spheroid halos of Population II stars, many of which are concentrated in globular clusters that orbit the galactic center.
Our galaxy, the Milky Way, is a spiral, with a Hubble sequence classification of Sbc (possibly SBb).
External Link:
Spiral Galaxies, SEDS Messier pages