Spiral galaxySpiral 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.
Spiral galaxies are so named due to the bright arms of star formation
within the disk that extend—roughly logarithmically
—from the bulge. Though sometimes difficult to discern, such as in flocculent spirals, these arms distinguish spiral galaxies from their lenticular
counterparts, which exhibit a disk structure but no evident spiral.
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).
Spiral Galaxies, SEDS Messier pages