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Massive Objects at the Centers of Galaxies

Massive Objects at the Centers of Galaxies. Roger Blandford KIPAC Stanford. An History. … 1961-2 Hoyle, Fowler - radio sources are powered by explosions involving superstars 1963 Hazard, Schmidt - quasars 1963 Kerr metric 1964 Zel’dovich & Novikov, Salpeter et al - black holes

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Massive Objects at the Centers of Galaxies

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  1. Massive Objects at the Centers of Galaxies Roger Blandford KIPAC Stanford

  2. An History • … • 1961-2 Hoyle, Fowler - radio sources are powered by explosions involving superstars • 1963 Hazard, Schmidt - quasars • 1963 Kerr metric • 1964 Zel’dovich & Novikov, Salpeter et al - black holes • 1965 Dent - variability

  3. More history • 1966 Rees - superluminal expansion • 1968 Wheeler - Black Hole • 1969 - Whitney….. - SLE measured • 1969 Lynden-Bell - dead quasars, disks • 1974 Balick & Brown, Lynden Bell & Rees • 1975 Kellermann Cygnus A - pc scale collimation => black hole

  4. Observational Evidence • Accretion disks • NGC 4258 masers => Keplerian • Molecular disks • Stellar Orbits • Velocity dispersion and rotation • Individual, disruption? • X-rays from inner disks • MCG 6-30-15 Fe =>maximal rotation? • Comptonized, synchrotron, inverse Compton • Variability • Blazar jets • Disks? • Winds • BALQ • ?

  5. M87 Halca

  6. Black Holes • Kerr Metric (not Kerr-Newman) • Mass m=M8AU=500M8s[=5Gm=17s] • Spin W = a / 2mr+ • Ergosphere • Reducible mass • Shrink smallest stable circular orbit • GR untested • Black hole is strongly curved space(time) outside horizon - not just the horizon • Use infalling coordinate systems not just Boyer-Lindquist

  7. Spin energy of a black hole Irreducible Radius Irreducible Mass Specific Angular Momentum Rotational Speed Gravitational mass

  8. Kerr Spacetime • Dragging of inertial frames • Physics of ergosphere very important • Need numerical simulation - MHD • Thin disk efficiency probably irrelevant to real disks; binding energy curve very shallow • Accretion Gap • Proper distance between horizon and marginally stable orbit 7m - 2m as a -> m

  9. Modes of Accretion and Sgr A* • LE ~1046M8 erg s-1 [~3 x 1044 erg s-1] • M’E ~1025M8 g s-1[~3 x 1023 g s-1] • Mass supply • M’ < 0.1 M’E : Thick, ion-supported disks [~1021 g s-1] • Mass accretion << Mass supply[~1018g s-1] • 0.1 M’E < M’ < 10 M’E : Thin, radiative disks • 10M’E < M’ : Thick, radiation-dominated disks

  10. Luminosity vs Supply Rate Brightest quasars 0 -2 L / LE -4 -6 Sgr A* -8 -4 -2 0 2 M’S / M’E

  11. Ion-Supported Thick Disks • Low mass supply and efficient angular momentum transport, low radiative efficiency • Adiabatic/altruistic/demand-limited accretion (ADIOS) • Most mass escapes in a wind carrying off the energy liberated by the accreting gas • Wind may be matter-dominated or magnetically-dominated [~ 1039 erg s-1] Transition radius

  12. Self-similar disk models • Gas dynamical model • Convective Disk • Gyrentropic structure • S(L), B(L) • Meridional circulation • Thermal Front • Mass, momentum, • energy conserved • Outflow carries off energy • Centrifugal funnel

  13. Relativistic Ion-supported Torus • Gyrentropic - S(L) • Asymptotes to self-similar non-relativistic disk • Similar discussion for transition to thin disk

  14. Magnetic Field • Magnetorotational Instability • Disk-Hole Connection • Magnetized Outflows • Extraction from Hole BMW

  15. Emission from Ion Torus • Trans-sonic, Alfvenic, relativistic differentially-rotating flow • =>particle acceleration easy! • =>Nonthermal emission • X-rays not thermal bremsstrahlung • cm emission from outer disk (jet?) • Radio/mm polarization

  16. Jets and Radio Sources • Energy (+ mass, angular momentum) exhausts • Fluid • Ions • Hydromagnetic • Relativistic MHD / Electromagnetic • Disordered • Ordered • Jets highlight the current flow • Sgr A* jet ? • Evolution of mass, momentum, energy along jet • Entrainment, dissipation and radiation

  17. 3-D, adiabatic MHD model DENSITY PRESSURE p,  Contours similar: BARYTROPIC Rotation on cylinders: Von Zeipel (azimuthally averaged) Hawley, Balbus & Stone 01

  18. 3-D, adiabatic MHD model n~108cm-3 P ~ 1 Pa NRMHD wind plus RMHD/EM jet Centrifugal force important Hawley & Balbus 02

  19. Pictor A Sgr A* Jet? B~100G, F~3PV I~300TA LEM~1030W Magnetically-pinched current? Magnetic reservoir Ohmic dissipation W . B constant

  20. Ultrarelativistic Jets • Powerful compact radio sources • Superluminal jets V ~ 0.99 c • Variable GeVg-ray source • eg 3C 279 - Lg ~ 1049 f erg/s >> Lrad • MKN 421 - 30 min variability at 1 TeV! • Intraday variability => V ~ 0.999(9) c • Refractive scintillation • Coherent emission? • Gyrocyclotron by mildly relativistic electrons? • Sgr A*may be a TeV source

  21. Why is Sgr A* interesting? • Very dark energy! • Why is the sun interesting? • Extreme accretion mode • Quantitative?! • Stellar dynamics • Cradle to grave • Things unseen • Complexity • Molecular gas, orientation, IRS13, SNR, magnetic environment….. • Black holes - strong field test of GR • (Sub)mmVLBI for black hole shadow • Periodicities?

  22. Summary • Sgr A* paradigm for slow accretion • Detailed MHz - TeV observation • Possibly best (and cheapest) laboratory for strong field GR • Radio astronomers have produced almost all the good, quantitative affirmations of weak field relativity. Why stop now? • Complexity of circum-nuclear gas flow, stellar dynamics

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