Extracting Energy from a BHmorsony/150/lectures/lecture22... · • Mass distribution must be...
Transcript of Extracting Energy from a BHmorsony/150/lectures/lecture22... · • Mass distribution must be...
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Extracting Energy from a BH
• Rotational energy stored in ergosphere – Can be extracted
• Penrose process: – mass falls in, splits in two – Half falls in, half falls out
with more energy
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Extracting Energy from a BH
• Blandford-Znajek process: – Magnetic field threads ergosphere – Plasma travels along field lines, is accelerated
in ergosphere
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Gravitational Waves
• Gravitational radiation • Binary inspiral • Evidence for gravity waves • Methods for direct detection
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Gravitational Radiation
• Gravity moves at the speed of light • Change is how mass is arranged
communicated out at speed of light
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Electromagnetic Radiation
• When charge is accelerated, it produces light
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Gravitational Radiation
• Only one charge in gravity, so no dipole radiation
• But, quadrupole moment can change and produce gravitational radiation
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Gravitational Radiation
• Only one charge in gravity, so no dipole radiation
• But, quadrupole moment can change and produce gravitational radiation
• Mass distribution must be asymetric
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Sources of gravitational waves
• Supernovae – asymmetric explosion
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Sources of gravitational waves
• Supernovae – asymmetric explosion • Binary stars, neutron stars, black holes
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Sources of gravitational waves
• Supernovae – asymmetric explosion • Binary stars, neutron stars, black holes • Merging neutron stars, black holes
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Sources of gravitational waves
• Merging neutron stars
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Sources of gravitational waves
• Merging neutron stars
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Sources of gravitational waves
• Merging black holes
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Sources of gravitational waves
• Merging black holes
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Gravitational Waves
• Gravitational waves carry away energy and angular momentum
• Eventually gravitational radiation will cause a binary to merge
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Evidence for gravitational waves
• Pulsar binaries • Pulsar in orbit with a neutron star of white
dwarf • Pulse period changes due to doppler shift as
it orbits
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Evidence for gravitational waves
• Pulsar binaries • Pulsar in orbit with a neutron star of white
dwarf • Pulse period changes due to doppler shift as
it orbits
• Over time, orbit gets closer, orbital period decreases
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Evidence for gravitational waves
• PSR B1913+16
• Discovered by Russell Hulse and Joseph Taylor in 1974
• Won Nobel Prize in 1993
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Direct detection
• As gravitational waves goes by, is stretches space
• Distance between points changes
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Methods for direct detection
• Need something of fixed size you can measure changes in
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Methods for direct detection
• Need something of fixed size you can measure changes in
• Gravitational waves will set off vibrations in a solid mass
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Methods for direct detection
• Need something of fixed size you can measure changes in
• Laser interferometer: – 2 beams of fixed length, at 90 degrees to each
other – Interference pattern will change if length of
arms changes
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LIGO
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LIGO
• 2 detector – Louisiana and Washington – 3000 km apart
• 4 km arms
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LISA
• Space interferometer
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LISA
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LISA