Transcript Massive Objects at the Centers of Galaxies Roger Blandford KIPAC Stanford An History • … • 1961-2 Hoyle, Fowler - radio sources are powered by explosions involving.

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
• 1965 Dent - variability
More history
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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
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
– ?
M87
Halca
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 BoyerLindquist
Spin energy of a black hole
Irreducible Radius
Irreducible Mass
 A
rO  

4



1 2
 2mO
Specific Angular Momentum
a  r W  m;
Rotational Speed
  WrO  0.71
Gravitational mass
2
O
m
mO
1  2
; mO  0.71m
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
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
Luminosity vs Supply Rate
Brightest quasars
0
-2
L / LE
-4
Sgr A*
-6
-8
-4
-2
0
M’S / M’E
2
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 magneticallydominated [~ 1039 erg s-1]
Transition radius
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
Relativistic Ion-supported Torus
•Gyrentropic - S(L)
•Asymptotes to self-similar non-relativistic disk
•Similar discussion for transition to thin disk
Magnetic Field
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Magnetorotational Instability
Disk-Hole Connection
Magnetized Outflows
Extraction from Hole
BMW
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
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
3-D, adiabatic MHD model
DENSITY
PRESSURE
p,  Contours
similar:
BARYTROPIC
Hawley, Balbus & Stone 01
Rotation on cylinders:
Von Zeipel
(azimuthally averaged)
3-D, adiabatic MHD model
n~108cm-3
P ~ 1 Pa
Hawley & Balbus 02
NRMHD wind plus RMHD/EM jet
Pictor A
Sgr A* Jet?
B~100G,
F~3PV
I~300TA
LEM~1030W
Magnetically-pinched current?
Magnetic reservoir
Ohmic dissipation
W . B constant
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
Why is Sgr A* interesting?
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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?
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