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