Presented By: Paul Grenning

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22 Φεβ 2014 (πριν από 3 χρόνια και 6 μήνες)

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Presented By: Paul
Grenning


Deflagration is the ignition and combustion


Gasoline deflagrates when lit with a match


Detonation is the explosive force or shock compression


Dynamite detonates


Created by White Dwarf Stars


Final stage in a stars life


Super dense stars with the approximate energy of our
sun but the size of our earth.


The White Dwarf reaches the ignition temperature for
carbon fusion


White Dwarf merges with a second star it will exceed
the temperature required for nuclear fusion and
release enough energy to create the
Ia

Supernova


Releases as much energy as our sun emits over its
entire life span


Cal Jordan


Robert Fisher


D. M.
Townsley


A. C. Calder


C.
Graziani


S.
Asida


D. Q. Lamb


J. W.
Truran


The primary theme of my
research is the fundamental
physics of turbulent flows,
and its application to a
variety of astrophysical
phenomena.


Interstellar Medium and
Star Formation


Computational Physics


Works at Dartmouth
college in MA in the
department of physics


My research interests lie
in refining stellar physics
via its application to
novel and dynamic
astrophysical systems


Visiting professor at
University Of Chicago


Assistant Professor at the
University Of Alabama in
the Department of
Physics and Astronomy


Their work is being done at the University of
Chicago's Center for Astrophysical
Thermonuclear Flashes


The scientists and engineers are using
Argonne’s super computer Blue Gene/P to
create the simulations


GCD (Gravitationally Confined Detonation)



To show the detonation conditions in a three
dimensional simulation in the GCD model is possible


In the past, extensive two
-
dimensional cylindrical
simulations have shown that detonation conditions are
robustly reached in the GCD model for a variety of
initial conditions


They believe that the conditions to create this type of
supernova can be better viewed in 3D rather than 2D


Type
Ia

Supernovae are “Standard Candles”


These types of supernovae have revealed that the rate at
which the universe is expanding is accelerating


This has led to the discovery of “dark energy”


The biggest concern is that we do not know the causes of
these supernovae


Current models include


Pure Deflagration (PD)


Deflagration To Detonation Transition (DDT)


Pulsational

Detonation (PD)


Gravitationally Confined Detonation (GCD)


Only one to show the detonation arise naturally


Simulations use FLASH 3.0


An adaptive mesh hydrodynamics code for modeling
astrophysical thermonuclear flashes (such as
Supernovae, X
-
Ray Bursts, and classical Novae)


Uses the (advection
-
diffusion
-
reaction)ADR flame
model


Numerically quieter


More stable


Exhibits smaller curvature effects


Leaves out nuclear burning outside the flame because
with it there would be too much overhead to show
such a robust simulation


Size of the flame bubble or thermonuclear flame
containing iron and other elements


Amount of iron and other elements


Resolution


Offset of the flame bubble from the center


Calculations based on fluid dynamics


Use the Rayleigh
-
Taylor instability model


Instability of and interface between two fluids of
different densities which occurs when the lighter fluid
pushes the heavier fluid


Often creates a mushroom shape as the fluids merge and
pass through each other and become R
-
T unstable


Initially stationary thermonuclear flame at some measured offset
from the center


The flame produces hot ash


Velocity increases due to buoyancy and a mushroom like bubble
appears.


Velocity is much slower at the center due to the intense
gravitational pull


Velocity continues to increase as it moves to the surface of the
star and spreads rapidly over the surface.


Prior to hitting the surface, the bubble is carrying a range of
densities of iron and other elements


The ash breaks out of but remains gravitationally bound to the
surface of the star


Collides at a point on the opposite side of the star from the
breakout location and incinerates the star



http://www.youtube.com/watch?v=5tjd9KAPais


The blue shows the approximate surface of the star and
the orange shows the interface between the star and
the hot ash produced by the flame.


http://www.youtube.com/watch?v=DBNy4WVm3D4


In the animation, green represents the approximate
surface of the star and the colors mark regions of high
temperature in the billions of degrees Kelvin.


They ran 7 simulations for this paper


Different starting parameters


Conservative conditions necessary for detonation are
achieved in all cases


Ran more simulations with higher resolution and
farther offsets from the center and received similar
results



Computationally the results were similar with their
previous 2D simulation.


The result is based on their conclusion that buoyancy
driven nuclear burning is dependent on fluid
dynamics on large scales.


It is the kinetic energy originating from the breakout
of the bubble of hot ash imparted to the
unburnt

surface layers of the star by the inwardly moving jet
generated by collision of the surface flows, that causes
the
unburnt

material to achieve the conditions for
detonation


Explosions produced large amounts of Nickel and
small amounts of other elements


Different mass stars could explain the high levels of
Nickel


The conditions are only for high
-
luminosity Type
Ia

supernovae


Multiple ignitions near the center of the star


Produces a lower luminous explosion


Jordan, Cal., Fisher, Robert., and
Townsley
, Dean, et al.
“Three Dimensional Simulations Of The Deflagration
Phase of the Gravitationally Confined Detonation
Model of Type
Ia

Supernovae.”
The Astrophysical
Journal.

681.2, (July 2008): 1448
-
1457


Fryxell
, B., Olson, K., and Ricker, P., et al. “FLASH: An
Adaptive Mesh Hydrodynamics Code for Modeling
Astrophysical Thermonuclear Flashes.”
The
Astrophysical Journal Supplement Series.

131.1,
(November, 2000): 273
-
334


http://en.wikipedia.org/wiki/Type_Ia_supernova