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Galaxies

Galaxies. Collection of stars…millions and billions of stars Distances measured in light years Distance light travels in 1 year 9.5 x 10 15 m (6 trillion miles) Galaxies are in groups called clusters ours is called the Local Group (>30 galaxies)

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Galaxies

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  1. 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

  2. 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

  3. 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

  4. Types of Galaxies • Elliptical • No spiral arms • Spherical or egg shaped • Mostly older stars, very little interstellar matter

  5. 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

  6. 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

  7. 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)

  8. 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

  9. 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

  10. 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…

  11. 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

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

  13. 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!

  14. 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

  15. 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”

  16. WMAP…background radiation

  17. 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)

  18. Timeline • Inflationary period: • Rapid expansion, temperature billions of degrees…way too hot even for atoms to exist! • 10-43 sec after • .0000000000000000000000000000000000000000001 seconds • 4 forces separate (electromagnetism, gravity, weak nuclear, strong nuclear) • Rules of physics we know now start to work

  19. 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)

  20. 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)

  21. 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 and stops • Oscillating Universe: Bang, Crunch, Bang, Crunch forever and ever

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