Massive Objects at the Centers of Galaxies

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Massive Objects at the Centers of Galaxies

• Roger Blandford
• KIPAC
• Stanford

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An History

• 1961-2 Hoyle, Fowler - radio sources are powered
  by explosions involving superstars
• 1963 Hazard, Schmidt - quasars
• 1963 Kerr metric
• 1964 Zeldovich Novikov, Salpeter et al - black
  holes
• 1965 Dent - variability

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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
  gt black hole

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Observational Evidence

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

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Black Holes

• Kerr Metric (not Kerr-Newman)
• Mass mM8AU500M8s5Gm17s
• 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

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Spin energy of a black hole
Irreducible Radius Irreducible Mass
Specific Angular Momentum
Rotational Speed
Gravitational mass
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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 -gt m

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Modes of Accretion and Sgr A

• LE 1046M8 erg s-1 3 x 1044 erg s-1
• ME 1025M8 g s-13 x 1023 g s-1
• Mass supply
• M lt 0.1 ME Thick, ion-supported disks 1021
  g s-1
• Mass accretion ltlt Mass supply 1018g s-1
• 0.1 ME lt M lt 10 ME Thin, radiative disks
• 10ME lt M Thick, radiation-dominated disks

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Luminosity vs Supply Rate
Brightest quasars
0
-2
L / LE
-4
-6
Sgr A
-8
-4
-2
0
2
MS / ME
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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
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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

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Relativistic Ion-supported Torus

• Gyrentropic - S(L)
• Asymptotes to self-similar non-relativistic disk
• Similar discussion for transition to thin disk

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Magnetic Field

• Magnetorotational Instability
• Disk-Hole Connection
• Magnetized Outflows
• Extraction from Hole

BMW
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Emission from Ion Torus

• Trans-sonic, Alfvenic, relativistic
  differentially-rotating flow
• gtparticle acceleration easy!
• gtNonthermal emission
• X-rays not thermal bremsstrahlung
• cm emission from outer disk (jet?)
• Radio/mm polarization

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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

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3-D, adiabatic MHD model
DENSITY
PRESSURE
p, ? Contours similar BARYTROPIC
Rotation on cylinders Von Zeipel
(azimuthally averaged)
Hawley, Balbus Stone 01
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3-D, adiabatic MHD model
n108cm-3 P 1 Pa
NRMHD wind plus RMHD/EM jet Centrifugal force
important
Hawley Balbus 02
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Pictor A
Sgr A Jet? B100G, F3PV I300TA LEM1030W
Magnetically-pinched current? Magnetic
reservoir Ohmic dissipation W . B constant
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Ultrarelativistic Jets

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

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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?

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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