Simulating Black Hole Lighthouses

05/16/2008 -
1:30pm to 2:30pm
Scott Noble
Speaker affiliation: 
Johns Hopkins
RIT, 78-2015

Accretion disks can be found around black holes of almost any size: from
galactic 1-10 solar mass black hole X-ray binaries to active galactic
nuclei  with black holes the mass of 10^6 - 10^9 suns.  Since
self-gravity of matter near the hole is often insignificant, the
hole's mass (in the absence of mass scales set by radiative processes)
is the only length scale in the problem and one can justifiably study
a whole class of objects simultaneously. I will present new simulation
results of 3D magnetohydrodynamic disks on a stationary curved background
using a recently developed 3D version of the energy-conserving HARM code. 
Since the code captures all energy dissipated in 3D disks as heat
and does not assume an isentropic equation of state, our new calculations
represent the most accurate picture to-date of a disk's thermodynamics near a
black hole.  In order to verify the validity of the standard radiative
efficient models by Novikov and Thorne, we implement a cooling function
to approximate losses from prompt emission.  We find that the
disk's local luminosity profile closely follows the Novikov-Thorne model
up to the radius of the innermost stable circular orbit (ISCO).
Within the ISCO  we find the luminosity increases steadily to the
horizon with no significant deviation from the average power-law profile.
Also, I will show comparisons between the cooled run and an otherwise
equivalent uncooled run; these comparisons are the first to show how
GRMHD disks change with disk thickness.  If time permits,
I will also present work on modeling the sub-millimeter emission from
plasma circling the supermassive black hole at the center of
our galaxy, Sgr A*.

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