Mitch Begelman JILA, University of Colorado ACCRETING BLACK HOLES and their jets.
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Transcript of Mitch Begelman JILA, University of Colorado ACCRETING BLACK HOLES and their jets.
![Page 1: Mitch Begelman JILA, University of Colorado ACCRETING BLACK HOLES and their jets.](https://reader030.fdocuments.net/reader030/viewer/2022033103/5697c0031a28abf838cc3883/html5/thumbnails/1.jpg)
Mitch BegelmanJILA, University of Colorado
ACCRETING BLACK HOLES and their jets
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WHY ACCRETING BLACK HOLES ARE INTERESTING
• Most efficient means of energy liberation in nearby universe
• Strong GR effects• Behavior of extremely relativistic plasmas• Liberated energy strongly affects galaxy
evolution
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3 FOCUS AREAS
• Accretion physics• Jet physics • Demographics (formation + feedback)
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ACCRETION PHYSICS
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4 FACTORS INFLUENCE ACCRETION• Angular momentum
– almost always too large to fall straight in – liberated energy transferred outward by torque
• Radiative efficiency– energy accumulates unless large fraction is radiated– low efficiency pressure forces dominate accretion flow
• Magnetic flux– Poloidal flux conserved: hard to accumulate– Catalyzes angular momentum transport – Global dynamics: magnetically arrested + supported disks– Drives jets
• Black hole spin– all spin energy extractable by magnetic fields– up to 29% of gravitating mass perceived at
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BLACK HOLE ACCRETION
l > GM/cl < GM/c
Radial (Bondi) Centrifugally choked
NO YESRadiatively efficient?
(Ṁ/ṀE)
RIAF Thin Disk
Nearly Keplerian?
Rotation important?
YESNO
SLIM DISKADAFADIOS
STARLIKE w/ narrow funnel
BH spin, Mag. flux?
Jets
YES
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ACCRETION PHYSICS• Super-Eddington (hyper-) accretion … when
disks look like stars
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SS433: A CLASSIC CASE OF HYPERACCRETION
Strong wind from large R
gtrap
Ein
RR
MM
3
3
10~
10 ~
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l/lKep
disk
ope
ning
ang
le
const.M
rM 0.74 0.88
• Gyrentropes: s(l)• Quasi-Keplerian
Inflates to axis when l ~ 0.74-0.88 lKep
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• Radiatively inefficient • Too much ang. mom. to fall straight in, not
enough to form a disk
• Density/pressure profiles steepen runaway accretion (>> LEdd), must produce jets or blow up
DISKLIKE STARLIKE ACCRETION
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EXAMPLES of STARLIKE ACCRETION
• (some) Tidal Disruption Events – fallback of debris from tidally disrupted star– evolution from super-Eddington sub-Eddington
• Gamma-Ray Bursts– mass supply from collapse of stellar envelope– enormously super-Eddington (> 1010)– fastest known jets ( ~ 102 - 103)
• SMBH seeds– hyper-accretion from inflated envelope (quasi-star)
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Super-Eddington TDE Swift J1644+57
Edd100~ L
Edd~ L
Tchekhovskoy et al. 2014
•Swift + Chandra light curves•L corrected for beaming•Radio “re-brightening” after ~ 4 months
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ACCRETION PHYSICS• Super-Eddington (hyper-) accretion … when disks
look like stars
• Highly magnetized disks
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A lot of thin disk theory doesn’t “fit”…
• Thermal/viscous instability not seen • Evidence for ultra-compact coronae • No explanation for hysteresis of XRB state transitions• Disks thicker and hotter than predicted• Inflow speeds faster than predicted• Quasars exist (!) despite predictions of disk self-gravity
HIGH DISK MAGNETIZATION A POSSIBLE SOLUTION!
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•Spectral “states”
•Follows a specific sequence
•Two-dimensional cycle = “hysteresis”
Fender, Belloni & Gallo 2004
LOW-HARD
HIGH-SOFT INTERMED.
QUIESCENT
X-ray Binary Evolution
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MAGNETIC DISK PHENOMENA• Poloidal flux accumulation
– advection from environment – buildup through stochastic fluctuations
• Viscous parameter correlated with poloidal field– the “second parameter” needed for hysteresis?
• Magnetically arrested disk (MAD)– Coupling to BH spin, jets
• Accretion disk dynamo
HIGH
LOW
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ACCRETION DISK DYNAMO
4poloidal 10
Salvesen et al. 2015
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ACCRETION DISK DYNAMO
3poloidal 10
Salvesen et al. 2015
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ACCRETION DISK DYNAMO
2poloidal 10
Salvesen et al. 2015
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JET PHYSICS
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JET PHYSICS• Magnetic vs. radiative propulsion
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Are jets always propelled by coherent magnetic fields?
cLJ
22
~
Magnetic flux threading Magnetic flux threading engineengine
Angular velocity of Angular velocity of engineengine
Jet power limited by amount of flux available
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Transient accretion events have access to a fixed amount of flux…
Tidal Disruption Event candidate Swift J1644+57:
Jet power: Lj > 1045 erg s-1 ~ 100 LE
Flux needed: > 1030 G-cm2
Flux available: ~ 1025 B3 (R/R)2 G-cm2
Collapsar Gamma-Ray Burst:
Jet power: Lj > 1050 erg s-1 ~ 1011 LE
Flux needed: > 1028 G-cm2
Flux available: ~ 1025 B3 (R/R)2 G-cm2
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JET MAGNETIC PARADIGM REVISITED• PRO
– magnetocentrifugal mechanism – BZ coupling to BH spin– blazar jets: not enough radiation pressure– electron cooling can quench gas pressure– radiation drag limits
• CON– insufficient magnetic flux!– magnetic propulsion inefficient at >> 1– GRBs, TDEs, quasi-stars: plenty of radiation– gas pressure OK if ions decoupled from electrons– radiation drag easy to shield against
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geff
MRI
Buoyant loops of B form inward corona
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geff
Reconnection
MRI
Reconnection converts energy to radiation
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geff
Reconnection
MRI
Entrainment (by rad’n force)
Mass-loading, collimation and acceleration
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geff
Reconnection
MRI
Entrainment (by rad’n force)
Self-shielding (from drag) few~
Self-shielding from radiation drag
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• Radiation driven jets, opaque fastest⁻ Lorentz factor ~ (L/LE)small power (~1/4??)
⁻ GRBs: L/LE ~ 1011 ~ 100 – 1000
• Magnetically driven jets, tenuous slower ⁻ ~ few 10s (e.g., blazars)
⁻ Poynting flux persists to large r
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JET PHYSICS• Magnetic vs. radiative propulsion
• Dissipation: shocks vs. reconnection
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• Shocks⁻ “Cold,” weakly magnetized jets⁻ quenched when Poynting flux ~ K.E.⁻ “diffusive” particle acceleration
• Reconnection ⁻ Favored in highly magnetized regions⁻ Poynting flux persists to large r ⁻ nonlinear particle acceleration
WHY DO JETS SHINE?
BOTH PRODUCE NONTHERMAL SPECTRA
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Mechanisms of Jet Dissipation
Particle-dominated
Poyntin Current-driven instabilities + reconnection
Internal shocks + Fermi acceleration
Shear instab. (KH, CD) + reconnection
Poynting-dominated
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Gamma-Ray Flares in the Crab (AGILE, FERMI)
Apr 2011 Buehler+
• ~1/yr for t ~ 1 day • h > 300 MeV • extremely hard• Eiso ~ 4 x 1040 erg
EVIDENCE OF RECONNECTION
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SYNCHROTRON
INVERSECOMPTON
(Buehler+2012)
>100 MeV! Apr.
2011
• Synchrotron emission• h > 160 MeV E > B, not shock acceleration
375 MeV!
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Gamma-ray (TeV) flares in blazars• Few minutes compact region of high energy
density and/or strong beaming• Hard flaring spectrum• Internal pair opacity bulk ~ 50-100 (BL Lacs)• External pair opacity r ~ pc scales (FSRQs)
Infer: Localized, extremely beamed radiation far from jet source (jets-in-a-jet).
Natural consequence of reconnection in highly magnetized jet.
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RECONNECTION RENAISSANCE
• All reconnection is fast!
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Time evolution of reconnection
Current sheet breaks up into small-scale plasmoids
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RECONNECTION RENAISSANCE
• All reconnection is fast! • Robust predictions of particle acceleration
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4.1ddN
Werner et al. 14
Extremely flat spectra: syn 0 for
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RECONNECTION RENAISSANCE
• All reconnection is fast! • Robust predictions of particle acceleration• “Kinetic Beaming” and rapid variability
– beaming & bunching a function of particle energy– Eiso depends on photon energy
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Solid angle containing 50% flux:
Energy-dependent synchrotron anisotropyAitoff projectiont = 397 ωc
-1
Ω50%/4π = 0.35
Ω50%/4π = 0.18
Ω50%/4π = 0.04
(Cerutti+ 2013)
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High-energy variability from particle bunching and anisotropy
Beam of high-energy particles sweeps across the line of sight intermittently bright symmetric flares
Density of γ >10 particles
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RECONNECTION RENAISSANCE
• All reconnection is fast! • Robust predictions of particle acceleration• “Kinetic Beaming”
– beaming & bunching a function of particle energy– Eiso depends on photon energy
• “Extreme Acceleration”– electrons trapped in current sheet E>B– εsyn > 160 MeV (radiation reaction limit)
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B. Cerutti & G. Werner
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These issues and more feed into demographic campaigns…
• What do hyperaccreting BHs look like? • How should we interpret the
spectra/vaiability of jet? • Spin bias
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Compilation of spin constraints
04/21/23 Extremes of BH Accretion 47
Reynolds (2014)Vasudevan et al. (2015)
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Spin Bias
04/21/23 Extremes of BH Accretion 48
Higher spin higher efficiency more luminousExpect high spin sources to be over-represented
Vasudevan et al. (2015)… also Brenneman et al. (2011)
n(a)~const
n(a)~a
n(a)~a2
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3x2 for the 2020s• Demographics
– find the rapidly accreting “seed” SMBHs– relate GRBs/SNe to BH masses and spins
• Accretion physics– discover the origin of QPOs and state transitions– understand whether and when the Eddington limit
is a limit• Jet physics
– determine whether jets are powered by BH spin and how they are mass-loaded
– discover how jets shine and what their radiation tells us about their power and composition
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A KILLER APP?
FINDING BLACK HOLES IN THEIR YOUTH