The Milky Way and other galaxies

Orion: star formation

Galaxy

• A collection of millions or billions of stars

• 100 billion galaxies or more may exist (1010 galaxies, each with 1010 stars)

We live in the Milky Way galaxy

Galaxy M73

The Milky Way

• Our solar system is near the outer edge of the milky way galaxy

• Because we are inside the Milky Way we can not see what it looks like from the outside.

Clusters

• Gravity pulls galaxies together

• Our ‘Local Group’

contains the Milky Way, Andromeda, and 30 other galaxies

Superclusters : the largest structure in the Universe, 1 million light years across

3 Types of galaxies• Spiral: has a bulge in

the center, with radiating arms and older stars are in the center, younger stars in arms

• Elliptical: spherical or egg- shaped, mostly older stars, reddish color

• Irregular: don’t have a defined structure

How galaxies begin

• The deeper into space we look, the farther back in time we see.

• Quasars, the most distant and radiant objects in space, may be the centers of young galaxies.

• They may have black holes at their centers

• Younger galaxies are blue

• Colors change as the gas and dust are consumed, and the stars cool

• Galaxies can collide,

changing their shape and generating new stars

• Older galaxies are red

I Zwicky 18 : young galaxy

How galaxies evolve

How galaxies age

Colliding galaxies

• NGC 6242 are galaxies that are circling each other.

• The colored centers are black holes

• At some point, they will merge

Photo by Keck observatory

Relative sizes of galaxies

Review

1. What are clusters?

2. What are the 3 types of galaxies?

3. What may be at the center of young galaxies?