new insights into type ia supernova explosions from large...

An Advanced Simulation and Computation (ASC) Academic Strategic Alliances Program (ASAP) Center

at The University of Chicago

The Center for Astrophysical Thermonuclear Flashes

SciDAC 2007Boston, MA, 27 June 2007

Don Q. LambNNSA ASC ASAP Flash Center

University of Chicago

New Insights into Type Ia Supernova Explosions from Large-Scale Simulations

The ASC/Alliances Center for Astrophysical Thermonuclear FlashesThe University of Chicago

NNSA Advanced Simulation and ComputingAcademic Strategic Alliance Program

ASC Academic Strategic AllianceCenters:

Focus on problems that involvecomplex multi-scale, multi-physicssimulations that require integrationof a number of academic disciplinesand software componentsAddress the difficult problems ofverification and validation of thesimulationsEducate and train students andyoung researchers in computationalscience


FLASH Capabilities Span a Broad Range…

Cellular detonation

Compressed turbulence

Helium burning on neutron stars

Richtmyer-Meshkov instability

Laser-driven shock instabilitiesNova outbursts on white dwarfs Rayleigh-Taylor instability

Flame-vortex interactions

Gravitational collapse/Jeans instability

Wave breaking on white dwarfs

Shortly: Relativistic accretion onto NS

Orzag/Tang MHDvortex

Type Ia Supernova

Intracluster interactions

MagneticRayleigh-Taylor



Cellular detonation










Type Ia Supernova



The FLASH code1. Parallel, adaptive-mesh refinement (AMR) code2. Block structured AMR; a block is the unit of

computation3. Designed for compressible reactive flows4. Can solve a broad range of (astro)physical problems5. Portable: runs on many massively-parallel systems6. Scales and performs well7. Fully modular and extensible: components can be

combined to create many different applications



Cellular detonation










Type Ia Supernova



The FLASH code1. Parallel, adaptive-mesh refinement (AMR) code2. Block structured AMR; a block is the unit of

computation3. Designed for compressible reactive flows4. Can solve a broad range of (astro)physical problems5. Portable: runs on many massively-parallel systems6. Scales and performs well7. Fully modular and extensible: components can be

combined to create many different applications

Development of the FLASH code was

made possible by nearly a decade of

funding and support by NNSA ASC

Academic Strategic Alliance Program


FLASH Is Being Used by Groups Throughout the World

US

Canada

US

GermanyItaly

Canada

Germany

Monthly Notices of the Royal Astronomical SocietyVolume 355 Issue 3 Page 995 - December 2004doi:10.1111/j.1365-2966.2004.08381.x

Quenching cluster cooling flows with recurrent hot plasma bubblesClaudio Dalla Vecchia1, Richard G. Bower1, Tom Theuns1,2, Michael L. Balogh1, Pasquale Mazzotta3 and Carlos S. Frenk1

UK

QuickTime™ and aTIFF (Uncompressed) decompressor

are needed to see this picture.



Netherlands


FLASH Is Being Used by Groups Throughout the World

US

Canada

US

GermanyItaly

Canada

Germany

Monthly Notices of the Royal Astronomical SocietyVolume 355 Issue 3 Page 995 - December 2004doi:10.1111/j.1365-2966.2004.08381.x

Quenching cluster cooling flows with recurrent hot plasma bubblesClaudio Dalla Vecchia1, Richard G. Bower1, Tom Theuns1,2, Michael L. Balogh1, Pasquale Mazzotta3 and Carlos S. Frenk1

UK





Netherlands

FLASH is being used by nearly 300

scientists around the worldto do

simulations in computational fluid

dynamics, astrophysics, cosmology,

plasma physics, ...; to

do scaling

studies, software development, etc.

in CS; and is a key acceptance test

for the IBM BG/P at ANL


What Are Type Ia Supernovae?

Supernova Cosmology Project

QuickTime™ and aYUV420 codec decompressor



What Are Type Ia Supernovae?

Supernova Cosmology Project



Peak luminositiesof most Type Ia SNeare similar -- making

them excellent“cosmic yardsticks”


Joint Dark Energy Mission

SNAP


Type Ia Supernovae

Accretion• Stellar binary evolution code with accretion

Smoldering• Subsonic convection

in core of white dwarf• Conductive heat

transport

Flame• Initially compressible

deflagration phase• DDT or expansion/recollapse• Conductive heat transport

Lightcurve• Free expansion of star • Multi-group (non-LTE)

radiation transport>108 yr

~seconds

~1000 yr

Ignition

Image copyrighted by Mark A. Garlick Image credit P. Garnavich/CfA


Type Ia Supernovae




transport





~seconds

~1000 yr

Ignition


Nuclear energy

powers the explosion


Type Ia Supernovae




transport





~seconds

~1000 yr

Ignition


Nuclear energy

powers the explosion

Radioactive decay of 56 N

heats expanding gas and

makes explosion visible


Central Ignition(single or multiple

Ignition points)

Off-Center Ignition(single or multiple

Ignition points)

Four Different Explosion Mechanisms Have Been Proposed

PureDeflagration

DeflagrationTo Detonation

Transition (DDT)

GravitationallyConfined

Detonation

Plewa, Calder, Lamb (2004);Townsley et al. (2007);Jordan et al. (2007)

Reineke et al. (1999, 2002);Schmidt et al. (2006)

Khokhlov (1991)

Khokhlov (1991);Gamezo et al.(2004, 2005)

PulsationallyDriven DDT


Movie of 3-D Simulation of Deflagration Phase of GCD Model

Jordan et al. (2007)




Detonation Conditions Are Robustly Produced by Inwardly Directed Jet


Detonation Conditions Are Robustly Produced by Inwardly Directed Jet

GCD model is only model so far in

which detonation occurs naturally;

i.e., without being put in by hand


Movie of End-to-End Simulation of GCDModel Including Detonation Phase




Computational Demandsof Type Ia SN Simulations

Following turbulent nuclear burning requires ~ 1-10 km resolution, whereas radius of star is 104 km --adaptive mesh refinement is therefore essentialHigh-resolution, 3-D, whole star simulations require ~ 100K-300K cpu-hrs on current machinesEach simulation ~ 200 MB/cpu-hrs; i.e., ~ 20-60 TB of dataWe will have used ~ 2M cpu-hrs on ASC machines and ~ 5 M cpu-hrs on Office of Science machines this year; expect to use 20-30M cpu-hrs next yearWe will have generated ~ 1 PB of data this year; ~ 3-5 PB of data next year


Importance of Verification and Validationof Type Ia Supernova Simulations

ConvectionDuring

SmolderingPhase

Rayleigh-Taylor -- Driven Turbulent Nuclear Burning

DeflagrationTo Detonation

Transition

GlobalValidation


Rayleigh-Taylor--Driven Turbulent Nuclear Burning

Zhang et al. (2007)

Nuclear flame is ~ 1 mmthick while resolution of best simulations is 1 km -- a factor of 108 larger!

A subgrid model of flame is therefore essential

The burning rate -- and thusthe result -- depends on model

Correct model to use is controversial -- further verification and validation studies are badly needed

Verification simulations we have done indicate burning rate is dominated by largest scales


Convergence With Resolution

Jordan et al. (2007)

Convergence with resolutionis excellent through bubble

breakout


Global Validation of Light Curves and Spectra Predicted by GCD Model

Comparison of U, V, B, R light curves predicted by GCD model and obs. of Type Ia Supernova SN 2001el

Kasen and Plewa (2006)

Comparison of spectra predicted by GCD model and obs. of Type Ia supernova SN 1994D





Comparison of spectra predicted by GCD model and obs. of Type Ia supernova SN 1994DLight curves and spectra

agree with observations





Comparison of spectra predicted by GCD model and obs. of Type Ia supernova SN 1994DLight curves and spectra

agree with observations

GCD model can produce

bright Type Ia supernovae;

can it produce faint ones?


Challenges in Getting to Petascale Type Ia Supernova Simulations

Efficiency on multi-core chips -- FLASH achieved 1.9 x speed-up on BG/L; we expect 3.6-3.8 x speed-up on BG/PScaling to 300K-1M cores -- FLASH scales wellto 65K cores (BG/L) and we expect the same to 128K cores, but 1M cores?Memory -- astro memory needs are largeI/O -- high bandwidth parallel I/O crucialData transfer -- 200Mbytes/cpu-hr generatedData storage -- many Petabytes, must be remoteScientific analysis pipeline -- must be remoteData archive -- Petabytes, must “compress”


Challenges in Getting to Petascale Type Ia Supernova Simulations

Efficiency on multi-core chips -- FLASH achieved 1.9 x speed-up on BG/L; we expect 3.6-3.8 x speed-up on BG/PScaling to 300K-1M cores -- FLASH scales wellto 65K cores (BG/L) and we expect the same to 128K cores, but 1M cores?Memory -- astro memory needs are largeI/O -- high bandwidth parallel I/O crucialData transfer -- 200Mbytes/cpu-hr generatedData storage -- many Petabytes, must be remoteScientific analysis pipeline -- must be remoteData archive -- Petabytes, must “compress”

Astrophysical simulations are often “discovery

science:” the phenomena are very complicated

and highly non-linear; we therefore don’t know

all of the questions we want to ask before we

see the data, so we must be able to explore it


ConclusionsFlash Center has conducted extensive verification and validationstudies of physical processes in Type Ia SNeCenter has carried out a series of high-resolution, 3-D, whole star simulations of Type Ia SNeThese simulations were made possible by a decade of support for development of the FLASH code and of computational resourcesprovided by the NNSA ASC Academic Strategic Alliance ProgramSignificant computational resources were also provided by the Office of Science INCITE programThey led to the discovery of the “gravitationally confined detonation” (GCD) model of Type Ia SNe -- the only model so far that detonates “naturally” (i.e., without being put in by hand)While almost surely not the final story, the GCD model reproduces many key observed properties of Type Ia SNe and is therefore promisingPetascale Type Ia SN simulations will enable us to get control overkey physical processes, but getting there will be challenging!

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