Galaxies• Collection of stars…millions and

billions of stars• Distances measured in light years

– Distance light travels in 1 year– 9.5 x 1015 m (6 trillion miles)

• Galaxies are in groups called clusters– ours is called the Local Group (>30

galaxies)• Clusters of clusters are called

superclusters• Classified by shape

Types of Galaxies• Spiral galaxies

– Have spiral arms made of gas and dust and stars

– Milky Way (our galaxy) is spiral– Our Sun is on a spiral arm about

26,000 ly from the center– Older stars tend to be at the center,

younger ones towards the outside

– Dust and gas called interstellar matter

•A picture of our galaxy from inside!

•Looking out towards the arm of the spiral

•It’s 100,000 ly across and 7,000 ly at the central bulge

Types of Galaxies• Elliptical

– No spiral arms– Spherical or egg shaped– Mostly older stars, very little interstellar

matter

Types of Galaxies• Irregular

– No regular shape

– Closest ones to Milky Way are irregular (Large and Small Magellanic Clouds)

– Mix of old and new stars

Quasars• Quasi-stellar objects• May be galaxies that are forming• May have a super massive black hole

at the center as matter enters the black hole, it is compressed and

gives off radio waves• Most distant objects in space

Galaxies change• Seem to start out as a quasar• Then take a spiral shape• Then lose the arms and become elliptical • Then lose shape and become irregular• This is just a guess (on the part of

scientists)• Change because of:

– Stars exploding– Use up gas and dust– Collisions (galaxy with galaxy)

Origin of Universe• Universe…all the space, energy and

matter that exists• Because things are so far from Earth,

and light takes so long to travel to us, when we look in the sky, we

look into the past• Most of space is empty … um …

space

Early thoughts• Steady State Theory: everything is

now as it always has been and nothing will ever change…stars, planets, galaxies are the same as they always have been and will never change

Early thoughts• Einstein…1916…theory of general relativity

redefines gravity and space to space/time– Implies that universe must be moving (not

static/unchanging), but doesn’t say expanding or contracting

• Lemaitre…1927…says universe should be expanding (observed red shift) and therefore once had a beginning

• People ignored Lemaitre in favor of Einstein until…

Edwin Hubble, 1929

• Noticed that light from stars is shifted towards red end of spectrum

• Means they’re moving away from us

• More it’s shifted, faster they’re moving

•Opposite is blue shift (means it’s moving towards us)

Edwin Hubble, 1929• Hubble noticed that most galaxies

are moving away from us and the farther they are, the faster they’re moving

• If go backwards, means everything was in a small point and exploded and is moving from that point out.

• Was called Big Bang to make fun of it and the name stuck!

Big Bang Theory• EVERYTHING (space, time, matter,

energy) was in one small point (singularity) that “blew up” and is still moving outwards today

• Not really an explosion, so much as a very rapid expansion…like

blowing up a balloon• About 13.7 billion years ago• Microwave radiation detected in the

1960’s supports this theory. It’s left over energy from the Big Bang

Penzias and Wilson

• In addition to Hubble’s evidence

• 1960’s discovered microwave radiation all throughout the universe, but couldn’t explain where it came from

• Only possible source is it’s left over from Big

Bang• Later shown not to be

“evenly spread”

WMAP…background radiation

Other evidence

• First elements to form should be simplest….Hydrogen and Helium, and that’s what most of the universe is (>99%)!

• Other heavier elements made by stars (fusion up to Iron) and supernovas (other heavier elements)

Timeline

• Inflationary period:– Rapid expansion, temperature billions of

degrees…way too hot even for atoms to exist!

• 10-43 sec after– .0000000000000000000000000000000000000

000001 seconds – 4 forces separate (electromagnetism, gravity,

weak nuclear, strong nuclear)– Rules of physics we know now start to

work

Timeline

• 10-35 seconds after– Protons and neutrons form– .00000000000000000000000000000000001

• 10-1 seconds after– Electrons form– .01 sec.

• 3 minutes after– 1st atomic nuclei form (H and He)– Temperature down to 1 billion degrees

• 300,000 years after– First atoms and light shines for first time

(CMBR)

What’s next?• Amount of mass will decide what’s going to

happen to the universe:– May continue expanding forever– May continue expanding and then stop at some

size– May expand to a point and then collapse and

explode again

• Hard to measure amt. to of mass. We see the effects (gravity) of some matter we can’t see, so we call it dark matter

(e.g. black holes)

What’s next?• Galaxies don’t seem to be slowing down (so

Big Crunch is doubtful, or we’re still in a period of expansion)

• Open universe: idea that not enough matter to keep it all together, and things keep expanding (like molecules from open jar)

• Closed universe: idea that enough mass to pull everything back in to Big Crunch

• Flat universe….expands to certain size andstops

• Oscillating Universe: Bang, Crunch, Bang, Crunch forever and ever