Mitch Begelman & Eric Coughlin JILA, University of Colorado ARE RELATIVISTIC JETS ALWAYS MAGNETIC?
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.
Mitch BegelmanJILA, University of Colorado
ACCRETING BLACK HOLES and their jets
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
3 FOCUS AREAS
• Accretion physics• Jet physics • Demographics (formation + feedback)
ACCRETION PHYSICS
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
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
ACCRETION PHYSICS• Super-Eddington (hyper-) accretion … when
disks look like stars
SS433: A CLASSIC CASE OF HYPERACCRETION
Strong wind from large R
gtrap
Ein
RR
MM
3
3
10~
10 ~
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
• 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
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)
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
ACCRETION PHYSICS• Super-Eddington (hyper-) accretion … when disks
look like stars
• Highly magnetized disks
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!
•Spectral “states”
•Follows a specific sequence
•Two-dimensional cycle = “hysteresis”
Fender, Belloni & Gallo 2004
LOW-HARD
HIGH-SOFT INTERMED.
QUIESCENT
X-ray Binary Evolution
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
ACCRETION DISK DYNAMO
4poloidal 10
Salvesen et al. 2015
ACCRETION DISK DYNAMO
3poloidal 10
Salvesen et al. 2015
ACCRETION DISK DYNAMO
2poloidal 10
Salvesen et al. 2015
JET PHYSICS
JET PHYSICS• Magnetic vs. radiative propulsion
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
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
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
geff
MRI
Buoyant loops of B form inward corona
geff
Reconnection
MRI
Reconnection converts energy to radiation
geff
Reconnection
MRI
Entrainment (by rad’n force)
Mass-loading, collimation and acceleration
geff
Reconnection
MRI
Entrainment (by rad’n force)
Self-shielding (from drag) few~
Self-shielding from radiation drag
• 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
JET PHYSICS• Magnetic vs. radiative propulsion
• Dissipation: shocks vs. reconnection
• 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
Mechanisms of Jet Dissipation
Particle-dominated
Poyntin Current-driven instabilities + reconnection
Internal shocks + Fermi acceleration
Shear instab. (KH, CD) + reconnection
Poynting-dominated
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
SYNCHROTRON
INVERSECOMPTON
(Buehler+2012)
>100 MeV! Apr.
2011
• Synchrotron emission• h > 160 MeV E > B, not shock acceleration
375 MeV!
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.
RECONNECTION RENAISSANCE
• All reconnection is fast!
Time evolution of reconnection
Current sheet breaks up into small-scale plasmoids
RECONNECTION RENAISSANCE
• All reconnection is fast! • Robust predictions of particle acceleration
4.1ddN
Werner et al. 14
Extremely flat spectra: syn 0 for
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
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)
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
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)
B. Cerutti & G. Werner
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
Compilation of spin constraints
04/21/23 Extremes of BH Accretion 47
Reynolds (2014)Vasudevan et al. (2015)
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
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
A KILLER APP?
FINDING BLACK HOLES IN THEIR YOUTH