Galaxies Beyond the Milky Way

Types of Galaxies There are Three main types of Galaxies: 1.Spiral (like the Milky Way) 2. Elliptical (Round without internal Structure) 3. Irregular (No structure at all, usually small)

Spiral Galaxies have a structure similar to the Milky Way. There are two subtypes Typical (S type) Have multiple arms Barred Spirals (SB type) With only two arms that are often partially straight

Spiral Galaxies vary from: Tight arms and a big bulge (Like the Sa type below) To Loose arms and a small bulge (like the Sd type above)

Ellipticals Ellliptical vary in shape from more spherical (E0) to very flattened (E7), to disk-like (S0)

Other differences between galaxy types Spiral Galaxies tend to be Of about the same size Full of interstellar dust and gas Composed of both younger (population 1) and Older (popualtion 2) stars Elliptical Galaxies Vary significantly in size have less interstellar gas and dust. Have only older (pop 2) stars Perhaps because they lack the gas and dust needed to form new stars

Hubble’s “Tuning Fork” Hubble thought that galaxies started as elliptical (E0) and changed into S types evolving into Spiral S types and then into an Irregular (Irr) type… we no longer believe that is so.