1. #23 Big Bang Theory The expanding universe and a quick galaxy review

3.  What do we know about the Milky Way, our own galaxy? The Milky Way Galaxy

4. The Central Black Hole Recent studies suggest that a black hole, with a mass of more than a million suns, probably exists at the very center of our galaxy.

5. The Expanding Universe  Late 1920s, Edwin Hubble discovered that the farther away a galaxy was, the faster it was moving away from Earth.  This concept came to be known as the expanding universe.

7. The Big Bang Theory  If the universe is expanding, it must have been smaller in the past than it is today.  Astronomers now believe the universe exploded outward from a single point.  This idea is known as the Big Bang Theory.

9. The Big Bang theory  The Big Bang theory says the universe began as a huge explosion between 10 billion and 20 billion years ago (most likely 13-14 bya.)  According to this theory, all matter and energy started in a space smaller than the nucleus of an atom.

11. Support for the BB theory:  cosmic background radiation  heat scattered from explosion  all of space same temp = -270ºC (only 3 above absolute 0)  universal expansion  all other galaxies are moving away from us & each other – ex) dots on balloon when inflating

12. More Evidence for the BB theory (We know the rate that stars convert Hydrogen to Helium thru nuclear fusion)  The proportion of H to He is consistent with the physics of the Big Bang.  If the universe were significantly older, there would be more heavy elements present compared to the % of H & He we see now.

15. This is the end …… Two main theories 1. Big crunch says lots of matter stop expanding due to gravity may start collapsing Big Bang could be a repeating pattern 2. Expansion forever* not enough matter ╚► so not enough gravity to stop expansion galaxies become more widely separated stars age & die universe will become cold & dark *recent observations suggest this one, but ?????