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Explore the mysteries of dark matter and dark energy in the universe and their critical role in the fate of the cosmos. Learn about the composition of the universe, the significance of dark matter and dark energy, and the latest research on WIMPs and MACHOs. Discover how observational evidence sheds light on the existence of dark matter and the accelerating expansion of the universe, shaping its ultimate destiny.
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Mass within Sun’s orbit: 1011MSun Observable stars and gas clouds: ~few 109MSun
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
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%
Spiral galaxies all tend to have flat rotation curves indicating large amounts of dark matter
The visible portion of a galaxy lies deep in the heart of a large halo of dark matter
measure the velocities of galaxies in a cluster from their Doppler shifts Mass is 50 x larger than the mass in stars!
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
Gravitational lensing of background galaxies also tells us the mass
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
MACHOs do not cause enough lensing events to explain all the dark matter
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
Gravity of dark matter is what caused protogalactic clouds to contract early in time
WIMPs don’t contract to center because they don’t emit photons, so they can not radiate away their orbital energy
Maps of galaxy positions reveal extremely large structures: superclusters and voids
Fate of universe depends on the amount of dark matter Critical density of matter Lots of dark matter Not enough dark matter
Amount of dark matter is ~25% of the critical density suggesting fate is eternal expansion Not enough dark matter
But expansion appears to be speeding up! Dark Energy? Not enough dark matter
Brightness of distant white-dwarf supernovae tells us how much universe has expanded since they exploded
