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

3. The Milky Way Galaxy
What do we know about the Milky Way, our own 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. 4

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. 5

7. This idea is known as 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. 7

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 bya.)
According to this theory, all matter and energy started in a space smaller than the nucleus of an atom. 9

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. 12

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 ?????