Title: Dark Matter, Dark Energy, and the Fate of the Universe
1Dark Matter, Dark Energy, and the Fate of the
Universe
2 Mass within Suns orbit 1011 MSun
Observable stars and gas clouds few 109
MSun
3Dark 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
4What 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
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6Spiral galaxies all tend to have flat rotation
curves indicating large amounts of dark matter
7The visible portion of a galaxy lies deep in the
heart of a large halo of dark matter
8measure the velocities of galaxies in a cluster
from their Doppler shifts
Mass is 50 x larger than the mass in stars!
9Clusters contain large amounts hot gas emits x
rays Temperature of hot gas tells us cluster
mass 85 dark matter 13 hot gas 2
stars
10Gravitational lensing of background galaxies also
tells us the mass
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14What 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
15MACHOs do not cause enough lensing events to
explain all the dark matter
16Why Believe in WIMPs?
- Theres not enough ordinary matter
- WIMPs could be left over from Big Bang
- Models involving WIMPs explain how galaxy
formation works
17?
Gravity of dark matter is what caused
protogalactic clouds to contract early in time
18WIMPs dont contract to center because they dont
emit photons, so they can not radiate away their
orbital energy
19Maps of galaxy positions reveal extremely large
structures superclusters and voids
20WIMP models agree better with observations
21Fate of universe depends on the amount of dark
matter
Critical density of matter
Lots of dark matter
Not enough dark matter
22Amount of dark matter is 25 of the critical
density suggesting fate is eternal expansion
Not enough dark matter
23But expansion appears to be speeding up!
Dark Energy?
Not enough dark matter
24Brightness of distant white-dwarf supernovae
tells us how much universe has expanded since
they exploded
25Accelerating universe is best fit to supernova
data