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March 14, 2007
Alan Calder
SUNY collaborators: M. Zingale, J. Lattimer, D. Swesty
The Physics of Type Ia supernovae
orThe Hows and Whys of Blowing up Stars
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Understanding Exploding Stars Helps Us Understand:
How big is the Universe?
Where are complex atoms produced?
What will be the final fate of the Universe?
What happens when stars die?
High-Z Supernova Search Team
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Outline
• Introduction to supernovae
• Taxonomy
• Observational
• Theoretical (two classifications)
• Thermonuclear Supernovae
• The problem
• Role of Rayleigh-Taylor Instability (basic physics)
• A new mechanism for igniting the detonation
• Studies of Rayleigh-Taylor Instability
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Astronomical Appearance
P. Nugent (LBNL)
Observations: light
curve, the observed
intensity of light, and
spectrum.
Spectrum provides
information about the
elements produced
during the event.
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Fairly Recent Galactic Supernovae
• SN 185 (RCW 86 is remnant?)
• 393 et al. observed by Chinese
• SN 1006 (SNR 327.6+14.6)
• SN 1054 (Crab Nebula)
• SN 1181 (pulsar 3C58?)
• SN 1572 Tycho’s Supernova
• SN 1604 Kepler’s supernova
• SN 1987a in Mangelanic Clouds
NASA/CXC/SAO
Tycho’s Supernova
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We observe remnants
NASA/CXC/Rutgers/J.Hughes et al
SN 1006 (SNR 327.6+14.6)
7NOT/Wein/Nowotny et al
SN 1054 (Crab)
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Crab in X-rays (left) and optical (right)
X-ray: NASA/CXC/ASU/J.Hester et al.; Optical: NASA/HST/ASU/J.Hester et al.
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Supernova Taxonomy (Observers)
SN IIn
“Abnormal” SNII
SN IIpec
M. Montes
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Supernova Taxonomy (Theorists)
• Core collapse
• Thermonuclear
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Supernova Taxonomy (Theorists)
• Core collapse:
• requires massive stars (m > 8-10 Msolar).
• Degenerate iron core exceeds Chandrasekhar limit.
• Protons absorb electrons and release neutrinos (electron capture)
• Leaves behind a remnant neutron star or black hole
• Associated with other events: GRBs, collapsars, hypernovae.
• SN II, Ib, Ic
• Thermonuclear:
• involves a white dwarf (or two).
• Thermonuclear burning incinerates the star.
• No compact remnant.
• SN Ia
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Type Ia Supernovae
• Brightness rivals that of the host galaxy-
L ~ 1043 erg/s
• Large amounts of radioactive 56Ni
produced- radioactivity powers the light
curve
• Occur less frequently than core-collapse
• No compact remnant
• Robust lightcurve- variations can be
described by a single-parameter function.
Allows for use as standard candles!
• Likely event- the thermonuclear
explosion of a C/O white dwarf.
Kim et al.
Chandra Obs.
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Favored SN Ia Scenario
• Mass accretes from a companion
onto a white dwarf that then ignites
thermonuclear burning.
• Nature of that burning has been the
fundamental problem for 30+
years.
• Is it a deflagration (subsonic
flame)?
• Is it a detonation (supersonic
flame)?
• Will all of star burn? Burn to
what?
• Can models reproduce observed
nuclear abundances and light
curves?
• Why is the light curve so uniform?
Is it really?
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Accretion• stellar evolution code with accretion/binary evolution code
Smoldering• subsonic convection in core of white dwarf• low Mach number flow solver• conductive heat transport
Flame/Explosion• initial deflagration• DDT or expansion/recollapse• FLASH (compressible module) with subgrid model for flame.
Light curve• free expansion of envelope
• multi-group (non-LTE) radiation transport
>108 yr~ seconds
~ 1000 yr
Mark A. Garlick P. Garnavich/CfA
Modeling SN Ia’s
ignition
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• Studying SN Ia requires large-scale (~1000s of processors for days) fluid
dynamics simulations for any hope of progress!
• Progenitor model
• Multi-physics:
• Reactive Euler equations with self-gravity
• Equation of state for degenerate matter
• Nuclear Energetics: 12C+12C; burn to Nuclear Statistical Quasi-
equilibrium (Si group); burn to Nuclear Statistical Equilibrium (Fe group).
• Flame model (width/radius < 10-9)
• Emission of ν’s result in energy loss, ∆Ye (neutronization)
• Eventually models must include:
• Realistic progenitor models
• Rotation
• Magnetic fields
Physics of Type Ia Supernovae
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Rayleigh-Taylor Instabilities (Basic Physics)
g
Light fluid
(hot ash)
Dense fluid
(cold fuel)
Density schematic:
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Aside: Mesh Adaptivity and R-T Instability
AMR allows an increased
range of scales in a
simulation by adding
resolution where it is
needed.
Calder, et al.
RTI increases the area
of the flame, thereby
boosting the burning
rate.
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Fluid Instability in a Type Ia Supernova
RTI accelerates the flame.
But is a deflagration alone
enough to produce an
explosion?
Subgrid model should
capture effects of RTI
on unresolved scales.
Note: Even with AMR, the
disparate scales of Ia
necessitate use of a model
flame and a sub-grid-scale
model for turbulent
combustion.
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• Physics of turbulent flames (deflagration)
• Rayleigh-Taylor instability growth vs. fire polishing
• Effects of shear (local and global – rotation)
Type Ia Supernovae as a Combustion Problem
Three-dimensional
reactive flow modeling
needed to get correct
physical behavior of the
system. � Realistic
subgrid model.
M. Zingale
1.5 x 107 g/cm3 1.0 x 107 g/cm3 6.67 x 106 g/cm3
Carbon mass fraction
fuel
ash
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Integrated Simulation of and Octant (3-d)
INCITE
Volume rendering
of flame front
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Deflagration Models: Incomplete Burning
Khokhlov (2001)
• Energy of explosion is too small
• Significant mass of unburned C+O
• No composition stratification:
complete mixing of Ni, Si, C+O
throughout the star
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3-D Delayed Detonation Model
Average chemical composition as function of radius
3-D pure deflagration
3-D deflagration followed by detonation
Ignited “by hand” at the center of the
pre-expanded star.
C/ONi
Mg
Si
Gamezo et al. (2003)
Resulting stratified compositions
are in better agreement with
observations!
NiC/O
Si
Mg
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Whole Star (3-d)
INCITE
Very different result from octant simulation!
Volume rendering
of flame front
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Off-Center Deflagration Simulation
• Entire 3-d star
• Effective resolution of grid:
122883
• Resolution: 4.0 km.
• 50 km radius ignition region offset
by 12 km
• Run on ~1000 processors of
ALC (LLNL)
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Off-Center Evolution: Expanding Ash Bubble
Bay Area Photos
Windows to the Universe
DOE
ASCI Flash
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Gravitationally Confined Detonation
• Run on IBM BG/L at Watson
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Recent Confirmation of (Some) Results
• Röpke, Woosley, Hillebrandt (astro-
ph/0609088) recently confirmed
many of these results.
• Found 2-d results more likely to
detonate.
• Despite this agreement, they
maintain that collisions of material
(GCD) “cannot serve as a robust
model for SNe Ia.”
• Future 3-d simulations will confirm or
refute this conclusion.
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…and that leads us to
QUESTIONS AND DISCUSSION
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Bibliography
• Flash Code:
• Fryxell et al., ApJS, 131, 273, 2000
• Calder, et al. proc SC2000 (Gordon Bell Prize)
• Antypas et al. in proc. Parallel CFD 2005, Deane et al. eds. , Elsevier
2006
• SN Ia and Flames:
• Calder et al. astro-ph/0405162
• Plewa, Calder, & Lamb ApJL 612, 37, 2004
• Brown, et al. Nuc. Phys. A 758, 451, 2005
• Vladimirova, Weirs, & Ryzhik, Combust Theory and Modeling 10,
727 (2006)
• Calder, et al. ApJ 635, 313, 2007.
• Townsley et al. in prep.