Electromagnetic and Radiative Processes Near Black Hole Event Horizon
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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)
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Living with black holes - artists’ impression
(images from http://www.musemessenger.com)
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Black holes are very simple objects
What do black hole have?
- a singularity - an event horizon
Schwarzschild radius
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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
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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
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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)
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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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QuickTime™ and a
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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
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Resonant scattreing in the relativistic frame work
constraints (conservation and covariant resonant conditions):
Juetter distribution
Fuerst & Wu (2004)
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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)
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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)
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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
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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).
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Emission from semi-opaque accretion tori
Wu et al. (2008)
Lines with different energies can resonate in semi-transparent tori
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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)
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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)
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Scattering dominated accretion tori around a black hole
(Fuerst 2005, PhD Thesis)
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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
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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!
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Black holes as particle scatterer
At infinity
Near the event horizon
Klein-Gordon plane waves
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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.
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Event horizon revisited
- boundary of no return - surface of infinite red-shift- surface at which waves piled up ……
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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)
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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
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What do we know about the black hole event horizon?What do we know about black holes?
?? ?
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I want to believe ……
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