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Lecture 24: Black holes: the Universe's ultimate lock box?

Lecture 24: Black holes: the Universe's ultimate lock box?. Hawking Radiation. Heisenberg uncertainty principle: D E D t S h/2 p Þ Energy need not be conserved over short periods, only on average

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Lecture 24: Black holes: the Universe's ultimate lock box?

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  1. Lecture 24:Black holes: the Universe's ultimate lock box?

  2. Hawking Radiation • Heisenberg uncertainty principle: DEDt S h/2p Þ Energy need not be conserved over short periods, only on average • Virtual particles: particle-antiparticle pairs created from vacuum energy fluctuations which quickly disappear • Virtual particles that can "steal" energy from elsewhere become real

  3. Hawking Radiation • Virtual pairs near a black hole can steal energy from the gravitational field • Tidal stresses accelerate one particle outward, one drops into event horizon • Energy of new particle comes from gravitational energy of BH, so BH mass must decrease • Black hole evaporates!

  4. Hawking Radiation • Energy for new particles comes from tidal stresses • Tidal effects must be large over short path lengths of virtual pairs • Smaller black holes have steeper gravitational gradients => Smaller black holes evaporate more quickly tevap = 1010(MBH /1012 kg)3 yr tevap(1Msolar) ~ 1065 yr

  5. Hawking Radiation • Black holes emit as black bodies • Temperature of black hole proportional to rate of radiation • TBH = 10-7 (Msolar / MBH) • T(1 Msolar) ~ 10-7 K • T(106 Msolar) ~ 10-13 K

  6. Exotica • White holes - a phenomenon analogous to a black hole from which light can only escape. No obvious way to make or power one • Wormholes - conduits between two points in spacetime. Unstable, difficult to avoid singularity without going faster than c, solutions with timelike paths only size of elementary particles. If they exist, probably not useful for travel since stable solutions require "exotic matter"

  7. A Practical Perspective • Two main types of black hole in the universe • Stellar mass black holes: created by the collapse of a massive star at the end of its life, ~3-100? Msolar • Supermassive black holes (SMBH): found in the centers of galaxies, power quasars and AGN, ~a few times 106 - 109 M

  8. Stellar Black Holes • Created from stars of more than ~30 Msolar • Detectable in binary systems • Normal or evolved star transfers mass to black hole via accretion disk • Measure orbital period and velocity of companion and use Kepler's laws to derive lower limits on mass • Neutron stars < 3 Msolar so any larger invisible companion must be black hole or unknown physics

  9. Stellar Black Holes

  10. Stellar Black Holes

  11. Stellar Black Holes • X-Ray Binaries • Viscosity (friction) of gas in disk heats up disk • A few to 40% of gravitational potential energy (= rest mass energy) liberated • Temperatures of ~105-106 K in inner disk • Spectrum peaks in soft x-rays • Optically thin material in corona or inner disk at >107 K gives hard x-ray emission • Some with relativistic jets • Luminosities of order 105 Lsolar

  12. Supermassive Black Holes • Active Galactic Nuclei (AGN) • Many types; most commonly discussed are radio galaxies, Seyferts, quasars, and QSOs • Large black holes at the centers of galaxies form at early epochs, possibly from collapse of dense stellar clusters, and grow by accretion over lifetime of universe • Luminosity from accretion disks as in X-ray binaries, but larger BH = lower temperature

  13. Supermassive Black Holes • AGN structure • Accretion disk at a few x 104 K, peak emission in UV (R ~ 100AU ~100 RS) • Hot, rarefied gas in x-ray halo or corona (R ~ 1-10 AU ~ RS) • Broad emission line region (BLR); clouds with velocities of 104 kms-1, indicate strong gravitational field (R ~ 0.01pc) • Dusty molecular torus in plane of disk (R ~ 0.1-1pc) IR emission

  14. Supermassive Black Holes • AGN structure continued • Narrow emission line region (NLR); clouds of ionized gas with widths of a few hundred kms-1 Seen in cones extending from ~50pc to 15kpc • Relativistic jets - accelerated by magnetic fields in disk to significant fraction of c. Looking head-on into quasar jets, see OVVs and BL Lacs • Jets in radio galaxies may extend ~1 Mpc

  15. Supermassive Black Holes

  16. Supermassive Black Holes

  17. Supermassive Black Holes

  18. Supermassive Black Holes

  19. Supermassive Black Holes • AGN characteristics • Emission over 21 orders of magnitude in frequency - from radio to g-rays • Range of luminosities, from barely discernable to > 1015 Lsolar, 10,000 times the luminosity of a bright galaxy • Radio quiet and radio loud • Often associated with starbursts, interacting galaxies, Luminous Infrared Galaxies (LIRGs, ULIRGs, HLIRGs)

  20. Supermassive Black Holes • Evidence • Kinematic evidence • Stellar motions in center of Milky Way • Stellar and gas motions in other galaxies • OH masers in NGC 4258 • All imply tremendous mass in a tiny area • Images of dusty torii and accretion disks • Only way of producing enough energy to make a quasar in so little space

  21. Supermassive Black Holes

  22. Supermassive Black Holes

  23. Supermassive Black Holes

  24. Supermassive Black Holes

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