Understanding Thermal Stability of Radiation-Dominated Disks
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Understanding Thermal Stability of Radiation-Dominated Disks and Radiative Efficiency of Global Relativistic Disks. with Omer Blaes, Shigenobu Hirose Scott Noble, John Hawley, Kris Beckwith. Understanding Thermal Stability of Radiation-Dominated Disks. =. =. 1. 6. 2. 1. 2. 2. 1. =.

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With omer blaes shigenobu hirose scott noble john hawley kris beckwith

Understanding Thermal Stability of Radiation-Dominated DisksandRadiative Efficiency of Global Relativistic Disks

with

Omer Blaes, Shigenobu Hirose

Scott Noble, John Hawley, Kris Beckwith


Understanding thermal stability of radiation dominated disks

Understanding Thermal Stability of Radiation-Dominated Disks


Radiation dominance is the natural state of the interesting portions of bright disks

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Radiation-Dominance Is the Natural State of the Interesting Portions of Bright Disks

Radiation pressure exceeds gas pressure for

That is, for the most interesting parts of all bright accretion disks around black holes


Yet a model predicts thermal instability when p r p g

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Yet a – Model Predicts Thermal Instability When pr > pg

$\int dz Q \propto p_r h$$

Energy conservation gives

The a model asserts

When radiation pressure dominates,

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Dissipation and pressure are correlated

Dissipation and Pressure Are Correlated

So why doesn’t the thermal instability take place ?


What does dimensional analysis really imply

What Does Dimensional Analysis Really Imply?

Pressure and stress are comparable, but does that mean pressure controls stress?

Orbital shear does work on magnetic field, magnetic field dissipates, heat becomes radiation----so magnetic energy and stress drive the pressure, not the other way around!


Evidence from simulation data

Evidence from Simulation Data

Magnetic leads

Radiation leads

Magnetic Energy vs. Radiation Energy


Explore with toy model

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Explore with Toy Model

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Results strongly resemble simulations

Results Strongly Resemble Simulations

Without any intrinsic pressure-stress correlation: n=s=0


Including a pressure magnetic energy correlation after the fact

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Including a Pressure/Magnetic Energy Correlation --- After the Fact

Thermal balance means

Independent of n


Which variables really control the stress

Which Variables Really Control the Stress?

As suggested by the structure of shearing-box simulations, S and W are the truly fundamental variables wherever the inflow time is the longest timescale.

Magnetic field intensity, and secondarily, the pressure, follow, with dissipation of magnetic energy driving the pressure, as regulated by the radiative loss rate.


Radiative efficiency of global relativistic disks

Radiative Efficiency of Global Relativistic Disks


Origin of traditional efficiency numbers the novikov thorne model

Origin of Traditional Efficiency Numbers:the Novikov-Thorne model

  • Full GR

  • Time-steady, axisymmetric, vertically-integrated

  • Energy and angular momentum conservation

  • Boundary conditions—

    energy: prompt radiation carries off dissipation

    angular momentum: zero-stress at ISCO

h = ut(ISCO)


Mhd stresses don t know to stop at the isco

MHD Stresses Don’t Know to Stop at the ISCO

(Thorne 1974): “In the words of my referee, James M. Bardeen (which echo verbal warnings that I have received from Ya. B. Zel’dovich and V.F. Schwartzman), ‘It seems quite possible that magnetic stresses could cause large deviations from circular orbits in the very inner part of the accretion disk….’”

It follows that the Novikov-Thorne radiative efficiency numbers may not be the last word when magnetic stresses are important.


Numerical procedure

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Numerical Procedure

  • Extend HARM (GR/MHD, total-energy, conservative) from 2-d axisymmetric to 3-d

  • Introduce toy-model optically thin cooling function:

    (1) rapidly radiates (almost) all the heat generated

    (2) allows aspect ratio regulation


A first result

A First Result

a/M = 0.9

H/r = 0.1

T = 15000 GM/c3


Surface brightness in the fluid frame

Surface Brightness in the Fluid Frame

averaged over 10000—12000M


Preliminary summary

Preliminary Summary

  • There is noticeable radiation beyond N-T

  • Dependence on H/r, a/M to be explored


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