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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.