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What are the two types of spiral galaxies?

Spiral galaxies have three parts:



  • Bulge: The bulge is a spherical structure located at the center of the galaxy.


  • Disk: The disk forms the "arms" of the galaxy and is composed of dust, gas, and younger stars.


  • Halo: The halo is a spherical structure surrounding the bulge and part of the disk. It contains old clusters of stars.

Spiral galaxies can be classified into two groups:



  • Barred: In barred spiral galaxies, the arms emerge from a bar of material that runs through the bulge. Barred spiral galaxies are designated by the letters "SB". 


  • Ordinary: In ordinary spiral galaxies, the arms emerge directly from the bulge. Ordinary spiral galaxies are designated by the letters "SA".

Lower case letters are used to further classify spiral galaxies by the tightness of their arms.

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