Electromagnetic and Radiative Processes Near Black Hole Event Horizon

Kinwah Wu (MSSL, University College London)Steven Von Fuerst (KIPAC, Stanford University) Warrick Ball (P&A, University College London)

Living with black holes - artists’ impression

(images from http://www.musemessenger.com)

Black holes are very simple objects

What do black hole have?

- a singularity - an event horizon

Schwarzschild radius

Do black hole exist? Who knows …… but ……

Astrophysical zoo of “black holes” ………

1. Stellar mass black holes

- dead corpses of very massive stars

2. Supermassive black holes

- monsters at the centres of galaxies

3. Intermediate mass black holes (?)

- “the new kids on the block”

ultra-luminous X-ray sources (ULX)

4. Primordial black holes

- fossils of the distant past(image from science@nasa)

a ULX in the starburst galaxy M82

What we have seen .… what we are believing ….

(image from http://chandra.harvard.edu/photo/2004/rxj1242)

Observational images

Artists’ production based on astrophysicists’ interpretation

X-ray lines from accretion disks around black holes

Time-averaged line profiles of Fe K alpha emission from the AGN MCG-6-30-15 obtained by the ASCA satellite.

from Fabian et al. (2000)

Relativistic energy shift in ray tracing: “Usual” line emission calculations

The standard recipe: - define the metric and calculate the geodesic - make a Keplerian thin disk (i.e. velocity profile of the emitters)- determine the energy shift relative to the observed at each disk pixel - sum the contribution of emission from each pixel

But, …. how about radiative transfer effects? … Absorption? Scattering? Also, ….. what if the disk is not geometrically thin or Keplerian? …

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Formulating general relativistic radiative transfer

Liouville’s Theorem

BoltzmannEquation Radiative Transfer

Equation in a Covariant Form

General Relativity

(Fuerst & Wu 2004, 2007; Wu et al. 2006)

- phase-space volume conservation - particle number conservation in the comoving frame

BBGKY Hierarchy

no scattering

Resonant scattreing in the relativistic frame work

constraints (conservation and covariant resonant conditions):

Juetter distribution

Fuerst & Wu (2004)

General relativistic radiative transfer- absorption and emission

Profiles of absorption and emission lines from thin accretion disks around Schwarzschild and Kerr black holes with a = 0.998, viewed at inclinations of 45o and 85o (top and bottom rows respectively). (Fuerst & Wu 2004)

General relativistic radiative transfer- angle dependent emission

Accretion-disk images showing the pitch angles of photons (in the local emitters’ frame) that can reach a distant observer. The disk images are viewed at inclination angles of 45o (left panels) and 85o (right panels). Disks around a Schwarzschild black hole are on the top row, and disks around a Kerr black hole (a = 0.998) are on the bottom row.

Wu et al. (2006)

Emission from 3D objects around a black hole

Fuerst and Wu (2007)

Profiles of emission lines from opaque relativistic accretion tori with an aspect ratio set by a velocity law, with index n = 0.232 and rk = 8rg as indicated in MRI accretion disk simulations

energy-shift torus image

i = 45o

i = 85o

Emission optically thick accretion tori

Fuerst and Wu (2007)

Energy-shift images of tori (n = 0.2) around Kerr black holes (a = 0.998), with a large aspect ratio such that the inner boundary of the emission surface reaches the black-hole event horizon. Viewing inclination angle i = 15o, 45o and 85o (panels in top row, from left

to right).

Emission from semi-opaque accretion tori

Wu et al. (2008)

Lines with different energies can resonate in semi-transparent tori

Time-dependent calculations

Synchrotron and free-free emission from accretion inflows and outflows in the vicinity of a Kerr black hole (obtained by GRMHD simulations).

Fuerst et al. (2007)

General relativistic radiative transfer in the presence of scattering

the radiative transfer equation in stationary space-time

first-order tensor moment equation

the energy “Doppler” shift factor

tensor moment function

+ higher-order moment equations …

General relativistic transfer in the presence of scattering - a global integral equation instead of a local differential equation

Fuerst (2005), Wu et al. (2008)

Scattering dominated accretion tori around a black hole

(Fuerst 2005, PhD Thesis)

Seeing is believing imaging black hole and shadowing

Ball and Wu (2008)

Shadows of background sky cast by a Schwarzschild black hole with spherical (left) and gaussian (right) planar matter distributions

Can all black holes be imaged by shadowing?

black hole

incident electro-magnetic plane waves

There are always some big photons which cannot be fit inside a black hole!

Black holes as particle scatterer

At infinity

Near the event horizon

Klein-Gordon plane waves

Black hole scattering

- Plane wave-like behaviour at infinity and near the black hole event horizon

Potential scattering:

One can define the emission and absorption coefficient of black hole. (cf radiative processes of atomic matter)

Black holes are not black after all … They are actually gray holes in disguise.

Event horizon revisited

- boundary of no return - surface of infinite red-shift- surface at which waves piled up ……

Making black hole event horizon in the laboratory

optical fibre

The first laser pulse to modify the property of the optical fibre

The second pulse, at a different wavelength, as the probing wave

an artificial event horizon (photon trapped surface) is developed at the leading edge of the first laser pulse

laser

Leohardt et al. (2007)

Electrodynamics near black hole event horizon

My own questions: How do information transfer near the event horizon? Can we have a classical treatment?What is the role of gravity?

My thought experiment: Suppose that we thread the optical fibre with a magnetic field, do the magnetic field on the left side and the right side of the laser induced event horizon communicate (classically)?

optical fibrelaser

What do we know about the black hole event horizon?What do we know about black holes?

?? ?

I want to believe ……

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