1. Chapter 21 Galaxy Evolution and Black Holes

2. We still can’t directly observe the earliest galaxies

3. What do observations show?
HST has photographed many lumps which may be the precursors to modern galaxies.
Observations show that the first galaxies formed as little as one billion years after the Big Bang.

4. Very young objects on the left. Family album of galaxies over time.

5. How did galaxies form?
Successful models of galaxy formation show that galaxies were born when gravity of pulled together denser regions of the universe
These smaller irregularly shaped regions merged to form protogalaxies.
Early in time gas is the U is almost uniformly distributed
Gravity draws gas into the denser regions of space as time passes
Protogalactic clouds form in the densest regions and go on to become galaxies

6. Why do galaxies differ?

8. Formation of a Spiral Galaxy

9. Formation of an Elliptical Galaxy

10. Stellar Birthrate and Galaxies

11. Collisions were more likely in the past because galaxies were closer together
Collisions may explain why ellipticals are found where galaxies are closer together

12. Modeling Collisions & HST

13. Are supermassive black holes and galaxies related?

14. Examples: Radio galaxies, Seyfert galaxies, Quasars and Blazars
The center of an unusually bright galaxy is called an active galactic nucleus (AGN)
Examples: Radio galaxies, Seyfert galaxies, Quasars and Blazars
Active Nucleus in M87

15. The type of AGN we see depends on viewing angle

16. Quasars are the most luminous AGN

17. Characteristics of AGNs
Super bright(L >1012 LSun)
Rapid changes (light from region smaller than SS)
Emit energy across a wide range of wavelengths (contains matter with wide temperature range)
Jets of plasma moving at near light speed

18. Accretion of gas onto a supermassive black hole appears to be the only way to explain all the properties

19. Jets come from twisting of magnetic field in inner part of accretion disk

21. Black Holes in Galaxies
Many nearby galaxies – maybe all– have supermassive black holes at their centers
These black holes seem to be dormant AGN’s
All galaxies may have passed through a quasar-like stage earlier in time

22. Galaxies and Black Holes
Mass of a galaxy’s central black hole is closely related to mass of its bulge