Galaxies

Beyond the Milky Way

Types of GalaxiesThere 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 subtypesTypical (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)

ToLoose 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)

starsPerhaps 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.