Supernova in images of Greg Thorne and Nick McCaw

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Supernova in images of Greg Thorne and Nick McCaw
Image of spiral galaxy NGC 3938 taken on April 7
for 29050 lab partners Thorne and
McCaw. Discovery was reported only ten days
earlier on March 27 of SN2005ay.
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Black Holes

• Observed properties of black holes
• Gravitational energy
• Rotating black holes
• Eddington luminosity
• Accretion disks
• Jets

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Black Holes

• Fundamental properties of black holes
• Mass
• Spin
• Charge zero for astrophysical black holes

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Observed properties of black holes
Luminosity Orientation Jets
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Gravitational energy
The Hoover dam generates 4 billion kilowatt hours
of power per year. Where does the energy come
from?
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Gravitational energy
Water falling down to the generators at the base
of the dam accelerates to 80 mph. The same water
leaving the turbines moves at only 10 mph. The
gravitational energy of the water at the top of
the dam is converted to kinetic energy by
falling. The turbines convert kinetic energy to
electricity.
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Gravitational energy
Black holes generate energy from matter falling
into them.
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Compared to a non-rotating black hole of the same
mass, the event horizon for a rotating black is

• smaller
• larger
• the same
• blue

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Rotating black holes

• For non-rotating black holes
• - event horizon is at the Schwarzschild radius
• - inner edge of the disk is at 3 Schwarzschild
  radii
• For maximally rotating black holes
• - event horizon is at ½ Schwarzschild radius
• - inner edge of the disk is at ½ Schwarzschild
  radius
• Schwarzschild radius 3 km (M/MSun)

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Luminosity

• Gravitational energy is converted to kinetic
  energy as particles fall towards BH
• Efficiency of generators
• Chemical burning lt 0.000001
• Nuclear burning lt 1
• Non-rotating black hole 6
• Rotating black hole 42

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Accretion disk
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In Active Galaxies the disk is surrounded by a
dusty torus
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Accretion disks
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The light from a quasar is emitted from a region
10 light-days across. What does this tell us
about the quasar?

• The brightness will change every day.
• The brightness will change every 20 days.
• The brightness will not change in less than 10
  days.
• The brightness will not change in less than 100
  days.

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Varieties of Active Galaxies

• Radio Galaxies big jets, no obvious BH
• Quasars jets and BH
• Blazars mainly see the jet

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Orientation
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Eddington Luminosity
Limit on the brightness of a black hole
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Eddington Luminosity
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Accretion disks

• Disks form because infalling matter has angular
  momentum.
• Accretion leads to release of gravitational
  energy.
• Inner regions of disks rotate very rapidly near
  the speed of light.
• The luminosity of a black hole is limited by its
  mass.
• Accretion disks of solar-mass and supermassive
  BHs are similar.

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Review Questions

• What are fundamental versus observed properties
  of black holes?
• What is the efficiency of a BH for conversion of
  matter to energy?
• What is the maximum luminosity for a BH of a
  given mass?
• Are the different types of Active Galaxies
  fundamentally different?