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

Dark Matter, Dark Energy, and the Fate of the Universe. Dark matter and dark energy. Dark Matter: An undetected form of mass that emits little or no photons (particles of light) , but we know it must exist because we observe the effects of its gravity

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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. Dark matter and dark energy Dark Matter: An undetected form of mass that emits little or no photons (particles of light), 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

  3. 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%

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

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

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

  7. 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

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

  9. Gravitational Lensing: • distribution of matter (such as a cluster of galaxies) between a distant light source and an observer, that is capable of bending the light from the source as the light travels towards the observer

  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 -Neutrino-a neutral subatomic particle with a mass close to zero 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 proto-galactic 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 -Orbital energy is based on a sum of the potential and kinetic energy divided by the reduced mass (treating 2 objects as 1)

  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. Re-collpasing, Critical and Coasting • Recollapsing (or closed) universe • If the mass density is greater than the critical density, the gravitation pull will eventually pull all the matter back. • critical (or flat) universe • If we have just the right amount of mass per unit volume (the critical density), the universal expansion will eventually stops.

  19. coasting (or open) universe • If the mass density is less than the critical density, then universe will expand forever

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

  21. But expansion appears to be speeding up! Is this caused by Dark Energy??? Not enough dark matter

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

  23. Accelerating universe is best fit to supernova data

  24. Crash Course in Astronomy • Dark Matter • Dark Energy and Matter • Neil deGrasse Tyson Dark Energy and Matter

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