Spiral Galaxies

Spiral galaxies are those galaxies which appear like flattened disks with a central bulge, usually with arms. There are three main types or classes of Spirals based on their shapes.

Spiral Galaxy Types

Spirals

Classes

  • Sa, Sb, Sc

Descriptions

  • Central Bulge, Arms. Class depends on how tight or loose the arms are.
Image of Andromeda Galaxy appears like a flattened disk with a central bulge.
Public Domain | Image courtesy of NASA.Image courtesy NASA

Barred Spirals

Classes

  • SB

Descriptions

  • An elongated bar of stars across the Central Bulge. Is the bar tearing the galaxy apart?
Image of NGC 613, a Barred spiral galaxy, appears like an elongated bar of stars across the Central Bulge.
NGC 613, Barred SpiralPublic Domain | Image courtesy of NASA.

Lenticular Spirals

Classes

  • S0
  • SB0

Descriptions

  • No Spiral Arms, but disk-shaped.Appear to be old when compared to other spirals
Image of NGC 2787, Lenticular Spiral galaxy is disk-shaped with no spiral arms.
NGC 2787, Lenticular SpiralPublic Domain | Image courtesy of NASA.