1. GALAXIES
A Place where stars hang out

2. Galaxy A large collection of stars held together by gravity Contain
Dust
Gas
Astronomers believe that there are about 50 billion (50,000,000,000) in the universe
Each galaxy contains billions/trillions of stars
Galaxy

4. Spiral galaxies # shaped like pin wheel 2nd most common type of galaxy
#Centeral bulge (nucleus) that stars revolve around filled with old stars and little material for stars to form
# Arms that extend from central area filled with gasses and dust for stars to form
It is now believed that in the center of all spiral galaxies is a Super Massive Black Hole
Spiral galaxies

5. Spiral galaxies

6. Pin wheel Galaxy

7. Sombrero galaxy - spiral

8. Elliptical galaxies smooth and featureless with round or oval shapes
Stars seem to move around a central location
very little gas and dust
Filled with older stars
Most galaxies in the universe are elliptical
Elliptical galaxies

12. Courtesy Hubble web site

13. Irregular galaxies Do not have a uniform (no regular shape) appearance
Filled with a lot of gas and dust
Lots or star formation
Young hot stars

14. Two Irregular companions: The Large and Small Magellinic Clouds

18. Evolution of galaxies Galaxies change over time
1. Irregular galaxies are believed to be forming
Filled with huge amounts of gas and dust and new young stars
2. Spiral Galaxies are believed to have formed from Irregulars
Area in center has little gas and dust a lot of older stars
arms are filled with regions of gas and dust and new stars forming
3. Elliptical galaxies seem to be the oldest
Filled with old stars and little evidence that any new stars can form the gases and dust have been used up

20. Colliding galaxies
Small galaxy believed to be colliding with the milky way

21. Milky Way Galaxy: our home
100,000 light years across
15,000 light years thick
Named by Greeks – whitish strips looked like split milk
On a very clear dark night it looks like a wide hazy strip stretching across the sky. This is a side way look at another spiral arm stretching thousands of light years across the sky

23. Milky way facts
Home to about 400 billion stars including our Sun and solar system
The Milky Way does not sit still, but is constantly rotating.
The Sun and the solar system moves with the arms as they rotate. The solar system travels at an average speed of 515,000 miles per hour
It will take our Solar System about 230 million years to travel all the way around the Milky Way.