1. Galaxies and the Universe
CHAPTER 30

2. Which galaxy do we live in?
Milky Way
Planet<Solar System<Galaxy<Local Group<Galaxy Cluser<Supercluster<Universe

3. Shape of the Milky Way The Milky Way is a spiral galaxy
It is thought that Supermassive Black Holes are at the center of most galaxies, Including the Milky Way
Because we are in it, we cannot see what it looks like.
Thought to look something like this one.
Can use radio waves to do almost an MRI of the galaxy
This is due to Radio Waves long wavelength.

5. Formation and Evolution of the Milky Way
Formed 13.2 billion years ago
Shortly after the Big Bang
Galaxy began as a spherical cloud in space
Rotation formed this into a disk-like shape

6. Dark Matter
Galaxies show evidence that there is an unknown substance, which is called Dark Matter
Made of a form of subatomic particle that interacts weakly with other matter

8. Types of Galaxies Spiral galaxies Elliptical galaxies Barred Spiral

9. The Local Group A small cluster of galaxies, including the Milky Way
Roughly 2 million ly across
About 40 known members
Milky Way and Andromeda are the largest

10. Groups of galaxies Large clusters (hundreds or thousands of galaxies)
Galaxies can collide

11. Supercluster
Larger cluster of galaxies

12. The Universe is expanding
Most galaxies have redshifts, meaning that they are moving away from us
Additionally, evidence shows that the further from us a galaxy is, the faster it is going.
Hubble’s Law
This shows us that the Universe is expanding in all directions.

13. Universe’s current age
13.7 billion years

14. Cosmology The study of the Universe and its evolution
Based on Einstein’s Theory of General Relativity
Lots and lots of math

15. The Big Bang Theory
The theory that the universe began tiny and has been expanding since
Scientific Theory=explanation with lots of evidence
Not an explosion
There was “nothing” before the Big Bang, because time itself did not yet exist
Time cannot exist without matter

16. What is the shape of the Universe?
The Universe is experiencing 2 opposite forces
The momentum of the outward expansion
The gravitational forces of the matter in the universe
What will happen will depend on which of these forces is stronger

17. Open Universe Expansion will never stop
This would happen if expansion > gravity

18. Closed Universe
If gravity > expansion, the universe will begin to contract
Will eventually collapse in on itself
Big Crunch

19. Flat Universe
If gravity=expansion, the rate of expansion will stop, and it will drift slowly apart forever.

20. How to determine which it is?
We need to know the Universe’s density
We don’t know this value
Most cosmologists think that the data is pointing to a flat universe
Good news?
Nope…
Will result in distant galaxies and stars disappearing, stars supernovaing and becoming black holes, and single atoms being stretched across lightyears.
When will this happen?
???

21. Cosmic Background Radiation
Electromagnetic Radiation left over from the Big Bang
If you turn a TV to a static station, about 1% of the “snow” is caused by the cosmic background radiation

22. Dark Matter and Dark Energy
Cosmologists estimate that the Universe is
21% Dark Matter
75% Dark Energy
Practically nothing is known about these materials.
Scientists know that they exist, but still do not know what they are or how they work.