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Galaxies: Shapes and Types

Let's start with what holds galaxies together. Galaxies are gravitationally bound systems of stars. Most are held together by a supermassive black hole. The center of our Milky Way is Sagittarius A, which has a mass 4 million times greater than the Sun. The Milky Way is 100,000 light years in diameter and is 2.5 million light years away from the nearest galaxy, the Andromeda Galaxy. Our galaxy has around 100-400 billion stars.

Type/Morphology Characteristics Examples Picture
Elliptical Ellipsoidal profile, low interstellar matter, largest type of galaxy, denoted by E Maffei 1
Spiral Spiral arms extending from center, dense interstellar matter, denoted by S Pinwheel Galaxy
Spiral Barred Central bar structure in center of galaxy, spiral arms extend from bar, denoted by SB Milky Way Galaxy
Lenticular In between elliptical and spiral, have a disk shape but no arms extending from center, denoted by SB0 or S0 Spindle Galaxy
Irregular No distinct shape, may have some structure or no structure, denoted by Irr-I or Irr-II NGC 1427A
Ring Mostly empty space, center with little matter, ring with many stars, denoted by S(r) Hoag's Object

Milky Way Galaxy
Type Diameter Contents Age
The Milky Way Galaxy is a spiral-barred galaxy. It has spiral arms extending from its core but it also has a defined bar reaching out from its center. Our galaxy is between 150,000 to 200,000 light years wide. The Milky Way contains 100-400 billion stars and 100 billion planets. It may also contain 10 billion white dwarfs, 1 billion neutron stars, and 100 million black holes. It is approximately 13.51 billion years old and could have been born as early on as possible.