1. Formation of Galaxies Spiral versus elliptical Young Universe Collisions and Interactions Starbursts Elliptical galaxies

2. Formation of a Spiral Galaxy

3. Formation of an Elliptical Galaxy

4. Stellar Birthrate in Galaxies

5. Formation of Galaxies This picture of galaxy formation is incomplete Mergers, collisions, and interactions between galaxies are very important in their formation, particularly in the early stages of the Universe (why?)

6. Expansion of the Universe The Universe is expanding This means that the Universe used to be smaller In the early stages of the Universe –there were more galaxies –they were closer together –therefore, they interacted more

7. Young Universe

11. In which type of galaxy are star’s orbits distributed in random directions? 1.elliptical galaxies 2.spiral galaxies 3.barred spiral galaxies 4.blue galaxies

12. Colliding galaxies

13. The Mice

14. Cartwheel galaxy

15. Seyfert’s Sextet

16. Interacting galaxies

18. Starburst galaxy – M82

20. Colliding galaxies Movie

21. Galaxy interactions Interactions can rip stars out of galaxies, producing tidal tails Interactions can disturb gas in and between galaxies, producing starbursts Collisions can randomize stellar orbits leading to the formation of elliptical galaxies

22. Formation of an Elliptical Galaxy Movie

23. Galaxy growth via interactions Galaxies initially form from mergers of several gas clouds Galaxies then are changed by interactions Galaxies grow gradually by galactic cannibalism Interactions disturb gas leading to starbursts Collisions can randomize stellar orbits leading to the formation of elliptical galaxies