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Dark Matter, Dark Energy, and the Fate of the Universe

Dark Matter, Dark Energy, and the Fate of the Universe. Mass within Sun’s orbit: 10 11 M Sun Observable stars and gas clouds: ~few 10 9 M Sun. Dark matter and dark energy.

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Dark Matter, Dark Energy, and the Fate of the Universe

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  1. Dark Matter, Dark Energy, and the Fate of the Universe

  2. Mass within Sun’s orbit: 1011MSun Observable stars and gas clouds: ~few 109MSun

  3. Dark matter and dark energy Dark Matter: An undetected form of mass that emits little or no photons, but we know it must exist because we observe the effects of its gravity Dark Energy: An unknown form of energy that is causing the universe to expand faster over time

  4. What is the Universe made of? • “Normal” Matter: ~ 4.4% • Normal Matter inside stars: ~ 0.6% • Normal Matter outside stars: ~ 3.8% • Dark Matter: ~ 25% • Dark Energy ~ 71%

  5. Spiral galaxies all tend to have flat rotation curves indicating large amounts of dark matter

  6. The visible portion of a galaxy lies deep in the heart of a large halo of dark matter

  7. measure the velocities of galaxies in a cluster from their Doppler shifts Mass is 50 x larger than the mass in stars!

  8. Clusters contain large amounts hot gas: emits x rays Temperature of hot gas tells us cluster mass: 85% dark matter 13% hot gas 2% stars

  9. Gravitational lensing of background galaxies also tells us the mass

  10. What is dark matter made of? • Ordinary Dark Matter (MACHOS) • Massive Compact Halo Objects: dead or failed stars in halos of galaxies • Extraordinary Dark Matter (WIMPS) • Weakly Interacting Massive Particles: mysterious neutrino-like particles The Best Bet

  11. MACHOs do not cause enough lensing events to explain all the dark matter

  12. Why Believe in WIMPs? • There’s not enough ordinary matter • WIMPs could be left over from Big Bang • Models involving WIMPs explain how galaxy formation works

  13. Gravity of dark matter is what caused protogalactic clouds to contract early in time

  14. WIMPs don’t contract to center because they don’t emit photons, so they can not radiate away their orbital energy

  15. Maps of galaxy positions reveal extremely large structures: superclusters and voids

  16. WIMP models agree better with observations

  17. Fate of universe depends on the amount of dark matter Critical density of matter Lots of dark matter Not enough dark matter

  18. Amount of dark matter is ~25% of the critical density suggesting fate is eternal expansion Not enough dark matter

  19. But expansion appears to be speeding up! Dark Energy? Not enough dark matter

  20. Brightness of distant white-dwarf supernovae tells us how much universe has expanded since they exploded

  21. Accelerating universe is best fit to supernova data

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