Bloody StonesBloody Stones

Towards an understandingTowards an understanding

of AGN enginesof AGN engines

Mike J. CaiASIAA, NTHU

April 4, 2003

What’s with the title?What’s with the title?

OutlineOutline

Introduction to Active Galactic Introduction to Active Galactic NucleiNuclei

Physics of accretion disksPhysics of accretion disks Black holesBlack holes General Relativistic General Relativistic

Magnetohydrodynsmics and jetsMagnetohydrodynsmics and jets

Basic Properties of AGNBasic Properties of AGN

High luminosity (10High luminosity (1043~4843~48erg serg s-1-1)) LLnucleusnucleus~L~Lgalaxygalaxy Seyfert galaxySeyfert galaxy LLnucleusnucleus~100 L~100 Lgalaxygalaxy QuasarQuasar

Very small angular sizeVery small angular size Short variability time scaleShort variability time scale Apparent superluminal motionApparent superluminal motion A lot more AGN’s at z>2.5A lot more AGN’s at z>2.5

Unified Model of AGN

Seyfert 1

Unified Model of AGN

Seyfert 2

Unified Model of AGN

Blazar

Accretion DiskAccretion Disk Disk geometryDisk geometry

Matter needs to lose angular momentum Matter needs to lose angular momentum to reach central black hole.to reach central black hole.

Interaction of different orbits will mix Interaction of different orbits will mix angular momentum.angular momentum.

Scale height is roughly h~r cScale height is roughly h~r css/v/vorborb.. The inner region is well The inner region is well

approximated by a perfect plasma.approximated by a perfect plasma. Unstable to rotation if d(rUnstable to rotation if d(r22)/dr<0.)/dr<0.

Angular Momentum Angular Momentum TransportTransport

Viscosity?Viscosity? Friction between adjacent rings can transport Friction between adjacent rings can transport

angular momentum outangular momentum out disk – hide our ignorancedisk – hide our ignorance

MHD WindsMHD Winds Magneto-centrifugal acceleration (bead on a wire)Magneto-centrifugal acceleration (bead on a wire)

Magnetic Turbulence (Balbus-Hawley Magnetic Turbulence (Balbus-Hawley instability)instability)

Gravitational RadiationGravitational Radiation

30 when unstable

2

12

022

0

0eff

r

r

zr

r

r

GM

Schwarzschild Black HolesSchwarzschild Black Holes

Static and spherically symmetric Static and spherically symmetric metric.metric.

ggrrrr=∞ defines horizon (r=∞ defines horizon (rSchSch=2M).=2M). Circular photon orbit at rCircular photon orbit at rphph=3M =3M

(independent of l).(independent of l). Last stable orbit at rLast stable orbit at rmsms=6M (l=6M (l22=12M=12M22).). Maximal accretion efficiency ~ 5.7%.Maximal accretion efficiency ~ 5.7%.

Kerr Black HolesKerr Black Holes Stationary and axisymmetric metricStationary and axisymmetric metric

Dragging of inertial frames (gDragging of inertial frames (gtt≠0).≠0). ggtttt=0 defines ergosphere.=0 defines ergosphere. ggrrrr=∞ defines horizon (M<r=∞ defines horizon (M<rHH<2M).<2M).

Circular photon orbitCircular photon orbit rrphph=M (prograde), 4M (retrograde) for a=M=M (prograde), 4M (retrograde) for a=M

Last stable orbitLast stable orbit rrmsms=M (prograde), 9M (retrograde) for a=M=M (prograde), 9M (retrograde) for a=M

Maximal accretion efficiency ~ 42%.Maximal accretion efficiency ~ 42%.

An Ant’s Impression of a Kerr Black HoleAn Ant’s Impression of a Kerr Black Hole

cos1

sinsep

How to Power AGN JetsHow to Power AGN Jets

Accretion onto a supermassive Kerr Accretion onto a supermassive Kerr black hole that is near maximum black hole that is near maximum rotationrotation

Extraction of the rotational energy of Extraction of the rotational energy of the black hole via Penrose or the black hole via Penrose or Blandford-Znajek processBlandford-Znajek process

Magnetocentrifugal accelerationMagnetocentrifugal acceleration Collimation of outflow by magnetic Collimation of outflow by magnetic

fields (through hoop stress)fields (through hoop stress)

Extracting Rotational Extracting Rotational Energy of a Black HoleEnergy of a Black Hole

A rotating black hole has an A rotating black hole has an ergosphere where all particles have to ergosphere where all particles have to corotate with the black hole.corotate with the black hole.

Penrose process: explosion puts Penrose process: explosion puts fragments into negative energy and fragments into negative energy and angular momentum orbits.angular momentum orbits.

Blandford-Znajek process: magnetic Blandford-Znajek process: magnetic field pulls particles into negative field pulls particles into negative energy and angular momentum orbits.energy and angular momentum orbits.

GRMHDGRMHD MHD assumption MHD assumption FFuu=0, =0, FF==dAdA

LLuuFF = 0 = 0 Field freezingField freezing

T = TT = Tfluidfluid++TTEMEM

Stationarity and axisymmetryStationarity and axisymmetryLL= ∂= ∂tt or or ∂∂

= invariant flux= invariant flux

Isothermal equation of state, p = Isothermal equation of state, p = Conservation of stress energy, TConservation of stress energy, T

0 0

GRMHDGRMHD Conserved quantitiesConserved quantities

= - A= - A0,0,/A/A,, (isorotation, no sum) (isorotation, no sum) E, L (energy & angular momentum)E, L (energy & angular momentum) n un uPP (injection parameter) (injection parameter)

uuTT = 0= 0 11stst law of thermodynamics law of thermodynamics

BBPPTT = 0= 0 uu2 2 = -1 (algebraic wind = -1 (algebraic wind

equation)equation) QQPPTT

= 0 = 0 Scalar Grad-Shafranov equation, Scalar Grad-Shafranov equation, determines field geometry (ugly)determines field geometry (ugly)

Open QuestionsOpen Questions

Do all galaxies go through an AGN phase?Do all galaxies go through an AGN phase?

How are AGNs fueled from their How are AGNs fueled from their environment?environment?

Bar driven inflow?Bar driven inflow?

Interacting galaxies?Interacting galaxies?

Where do supermassive black holes come Where do supermassive black holes come from?from?

Is GRMHD the ultimate answer to jets?Is GRMHD the ultimate answer to jets?

Can stones actually bleed?Can stones actually bleed?