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

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1 The Center for Astrophysical Thermonuclear Flashes New Insights into Type Ia Supernova Explosions from Large-Scale Simulations Don Q. Lamb DOE NNSA ASC ASAP Flash Center University of Chicago Physics Colloquium Chicago, IL 1 November 2007 An Advanced Simulation and Computation (ASC) Academic Strategic Alliances Program (ASAP) Center at

2 People Who Have Done the Work Management Group Lamb (Director / PI) Cattaneo, Dupont, Lusk (Associate Directors) Dubey (Applications) Dupont (Validation) Eder (Administrator) Fisher (Astrophysics) Graziani (Statistics) Papka (CS/Viz) Applications Dubey, Lead Brune* Daley Lee Reid Rich Riley Weide Baron Hauschildt Kasen Malony Shende CS/Viz Papka, Lead Alford Bair Beckman Chan Foster Gallager Glendenin* Hereld Hudson Kumuran Lusk Norris, J Ross Stevens SN Ia Validation Fisher, Lead Simulations Observations Brown Blondin Graziani Frieman Hearn Kessler Hicks* Kirshner Jordan Miknaitis Khokhlov Phillips Kravtsov Suntzeff Lamb Wang Meakin Wood-Vasey Seitenzahl* Townsley Truran ZuHone* Predictive Science Methodologies Graziani, Lead Anitescu Hovland Lamb Loredo Norris, B. Reid Stein Laboratory Validation Dupont, Lead Abarzhi Anderson Bonazza Cattaneo Constantin Hearn Kadanoff Oakley Ryzik * Student Subcontractor Current Flash Center Staff External Collaborator Current External Collaborator Simulations Baron Branch Cooray Hauschildt Heitmann Holz Kasen

3 FLASH Capabilities Span a Broad Range Shortly: Relativistic accretion onto NS Wave breaking on white dwarfs The FLASH code Compressed turbulence 1. Parallel, adaptive-mesh refinement (AMR) Type code Ia Supernova 2. Block Gravitational structured collapse/jeans AMR; instability a block is the unit of computation 3. Designed for compressible reactive flows 4. Can solve a broad range of (astro)physical problems 5. Portable: runs on many massively-parallel systems Development of the FLASH code was made possible by nearly a decade of funding andsupport by NNSA ASC Academic Strategic Alliance Program 6. Scales and performs well Laser-driven shock instabilities Nova outbursts on white dwarfs Rayleigh-Taylor instability 7. Fully modular and extensible: components can be combined to create many different applications Flame-vortex interactions Intracluster interactions Magnetic Rayleigh-Taylor Cellular detonation Helium burning on neutron stars Orzag/Tang MHD vortex Richtmyer-Meshkov instability

4 QuickTime and a TIFF (Uncompressed) decompressor are needed to see this picture. Italy Canada FLASH Is Being Used by Groups Throughout the World Germany QuickTime and a TIFF (Uncompressed) decompressor are needed to see this picture. US US FLASH is being used by nearly 300 scientists around the world to 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 Monthly Notices of the Royal Astronomical Society Volume 355 Issue 3 Page December 2004 doi: /j x Netherlands UK Quenching cluster cooling flows with recurrent hot plasma bubbles The Claudio ASC/Alliances Dalla Vecchia Center 1, Richard for G. Astrophysical Bower 1, Tom Theuns Thermonuclear 1,2, Michael L. Flashes Balogh 1, Pasquale Mazzotta The University 3 and Carlos of S. Chicago Frenk 1 Canada Germany

5 What Are Type Ia Supernovae? QuickTime and a YUV420 codec decompressor are needed to see this picture. Supernova Cosmology Project

6 What Are Type Ia Supernovae? Peak luminosities of most Type Ia SNe are similar -- making them excellent cosmic yardsticks QuickTime and a YUV420 codec decompressor are needed to see this picture. Supernova Cosmology Project

7 Calibration Using Empirical Correlation Between Peak Brightness and Duration Peak brightnesses of Type Ia supernovae vary by roughly 2 mag = factor 5 Using empirical correlation between peak brightness and duration, variation can be reduced to about 15%

8 Discovery of Dark Energy Distant Type Ia supernovae appear dimmer than is possible for any Universe with non-zero Ω Λ. This led to the discovery that rate of expansion of universe is accelerating and thus to discovery of dark energy.

9 Constraints on Cosmological Models Currently three sources of information constrain cosmological models: Cosmic Microwave Background: Type Ia supernovae: Galaxy clustering and dynamics: Ω Μ + Ω Λ Ω Μ Ω Λ Ω Μ

10 Concordance Cosmological Model All three sources of information are consistent with Ω M ~ 0.3 Ω Λ ~ 0.7. We live in a low mass, flat, accelerating universe dominated by Dark Energy.

11 Effects of Dark Energy Primary effect of Dark Energy is on the expansion rate of the universe:. (R/R) 2 = H(z) 2 = H 02 [Ω M (1+z) 3 + Ω DE (1+z) 3(1+w) ] -- assuming a flat universe so that Ω DE = 1 Ω M

12 Values of w and w Predicted by Models of Dark Energy Courtesy of Michael Turner

13 Current Constraints on Properties of Dark Energy Data consistent with QuickTime and and aa TIFF (Uncompressed) decompressor are are needed to to see see this this picture. Ω M ~ 0.3 Ω Λ ~ 0.7 w ~ -1 We live in a low-mass, flat accelerating universe dominated by Dark Energy that behaves a lot like a vacuum energy. Tegmark et al. (2003)

14 DOE Dark Energy Mission SNAP

15 Type Ia Supernovae Image copyrighted by Mark A. Garlick Accretion Stellar binary in which main sequence star transfers mass onto white dwarf Smoldering Subsonic convection in core of white dwarf Heat transport is by electron conduction >10 8 yr Radioactive decay of 56 N heats expanding gas and makes explosion visible ~1000 yr Ignition Image credit P. Garnavich/CfA Lightcurve Free expansion of star Radioactive decay of nickel heats the ejecta This causes the ejecta to glow, which makes the supernova visible ~seconds Nuclear energy powers the explosion Flame Nuclear burning initially due to laminar flame Buoyancy driven turbulence increases nuclear burning rate Transition from deflagration to detonation occurs, causing the star to explode

16 Impact of Pre-Expansion on Nucleosynthetic Yield of Supernova Intermediate-Mass Nuclei Intermediate-Mass Nuclei Nickel and Other Iron-Peak Nuclei Nickel and Other Iron-Peak Nuclei Products of nuclear burning essentially depend only on density at which burning occurs -- iron-peak nuclei at high densities, intermediate mass nuclei at lower densities

17 Scales in Type Ia Supernova Problem Type Ia supernovae are a multi-scale problem: Spatial scales from 10-3 to cm Temporal scales from to 10 6 sec Temperatures from to 10 4 K Densities from 10 9 to 10-3 g/cc

18 Key Physical Processes in Type Ia Supernovae Equation of state of plasma at high ρ and T Convection during pre-supernova smoldering phase Rayleigh-Taylor-driven mixing Turbulent nuclear burning Detonation produced by converging shock Radiation transfer in high-t, high-velocity plasma

19 Four Different Explosion Mechanisms Have Been Proposed Central Ignition (single or multiple Ignition points) Pure Deflagration Off-Center Ignition (single or multiple Ignition points) Gravitationally Confined Detonation Deflagration To Detonation Transition (DDT) Reineke et al. (1999, 2002); Schmidt et al. (2006) Plewa, Calder, Lamb (2004); Townsley et al. (2007); Jordan et al. (2007) Pulsationally Driven DDT Khokhlov (1991); Gamezo et al. (2004, 2005) Khokhlov (1991)

20 Deflagration Phase of GCD Model of Type Ia Supernovae Jordan et al. (2007)

21 Deflagration Phase of GCD Model QuickTime and a YUV420 codec decompressor are needed to see this picture.

22 Initiation of a Detonation Wave QuickTime and a decompressor are needed to see this picture. Seitenzahl et al. (2007)

23 Images of 2-D Simulations of Detonation Phase of GCD Model Inwardly directed jet punches into the stellar surface, causing matter ahead of the jet to reach temperatures T > 3 x 10 9 K and densities > (1-2) x 10 7 g/cc in the jet Detonation starts in the high-t, high-density matter just ahead of the jet Meakin et al. (2007)

24 Images of 2-D Simulation of Detonation Phase of GCD Mechanism Meakin et al. (2007)

25 Deflagration Plus Detonation Phase of GCD Model QuickTime and a YUV420 codec decompressor are needed to see this picture.

26 Movie Showing Hot Ash for Case of Multiple Ignition Points QuickTime and a YUV420 codec decompressor are needed to see this picture. Jordan et al. (2007)

27 Movie Showing Hot Material for Case of Multiple Ignition Points QuickTime and a YUV420 codec decompressor are needed to see this picture. Jordan et al. (2007)

28 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

29 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 Light curves and spectra agree with observations Supernova SN 2001el GCD model can produce bright and dim Type Ia supernovae Comparison of spectra predicted by GCD model and obs. of Type Ia supernova SN 1994D Kasen and Plewa (2006)

30 Predictions of Pure Deflagration and DDT vs. GCD for Composition of Star Smoothly Stratified Composition Turbulently Mixed Inhomogeneous Composition Turbulently Mixed Inhomogeneous Composition Smoothly Stratified Composition Recent polarization (Wang et al. 2006, 2007) and spectroscopic observations (e.g., Gerardy et al. 2007) imply a compositional structure like this Pure Deflagration and DDT Models GCD Model

31 Goals of Flash Center for Predictive Science Motivated by the many things that the SN Ia problem and the Stockpile Stewardship Program have in common, and the importance of the SN Ia problem for Dark Energy, the three overarching goals of the Flash Center for Predictive Science are: To develop predictive science methodologies able to handle large, complex, and computationally demanding simulations that must be compared to large data sets, and incorporate these methodologies into SIMPI, a fully modular, extensible code To transform the SN Ia field through rigorous, systematic validation of current SN Ia models, using the SIMPI code, the integrated simulation pipeline (of which the FLASH code is the key component), and high-quality data from three world-class observing teams To educate and train young people in predictive science

32 Four Different Explosion Mechanisms Have Been Proposed Central Ignition (single or multiple Ignition points) Pure Deflagration Off-Center Ignition (single or multiple Ignition points) Gravitationally Confined Detonation Deflagration To Detonation Transition (DDT) Reineke et al. (1999, 2002); Schmidt et al. (2006) Plewa, Calder, Lamb (2004); Townsley et al. (2007); Jordan et al. (2007) Pulsationally Driven DDT Khokhlov (1991); Gamezo et al. (2004, 2005) Khokhlov (1991)

33 SN Ia Simulation Pipeline

34 Challenges to Validation of Type Ia Supernova Simulations Large, 3-D, multi-scale, multi-physics, integrated simulations Some key physical processes are not fully understood (e.g., turbulent burning during smoldering phase, buoyancy-driven burning during deflagration phase,ddt) Size of input parameter space is large (e.g., C/O ratio in core of WD, number of ignition points, location of ignition points, rotation) Size of output parameter space is large (e.g., light curves at ~10 wavelengths in UV, optical, and IR; 1Å resolution spectra covering 3,000-7,000 Å; continuum and line polarization) We cannot do experiments, so cannot select events nor instrument them; we therefore do not have key data High fidelity, 3-D, end-to-end simulations are expensive (~50-100K cpu-hours for moderate resolution simulations on current machines); therefore, we cannot afford as many as desired

35 Predictive Science Flow Chart

36 Validation Goals We plan to answer the following scientific questions: Which current Type Ia supernova models are consistent with observations? What values of model input parameters are consistent with observations and what are the associated uncertainties in them? How do Type Ia supernovae explode? What correlations exist among model output parameters? What are the properties of Dark Energy? We expect to predict important correlations among observational parameters that can be used to make Type Ia supernovae more accurate standard candles We have partnerships with SDSS Supernova Survey Project, Carnegie Supernova Survey Project, and CfA Supernova Group, who are providing us with high-quality photometric and spectroscopic data on nearby Type Ia supernovae

37 Computational Resources

38 Conclusions Flash Center has carried out a series of high-resolution, 3-D, whole star simulations of Type Ia supernovae These simulations were made possible by a decade of support for development of the FLASH code and of computational resources provided by the NNSA ASC Academic Strategic Alliance Program Significant computational resources were also provided by the Office of Science INCITE program They 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 the detonation 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 promising Flash Center has launched an effort to rigorously and systematically valid current Type Ia supernova models with the goal of helping to make them more accurate standard candles for determining the properties of Dark Energy

39 Rayleigh-Taylor--Driven Turbulent Nuclear Burning Zhang et al. (2007) Nuclear flame is ~ 0.1 mm thick while resolution of best simulations is 1 km -- a factor of 10 8 larger! A subgrid model of flame is therefore essential The burning rate -- and thus the 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

40 Convergence With Resolution Convergence with resolution is excellent through bubble breakout Jordan et al. (2007)

41 Importance of Verification and Validation of Type Ia Supernova Simulations Convection During Smoldering Phase Rayleigh-Taylor -- Driven Turbulent Nuclear Burning Deflagration To Detonation Transition Global Validation

42 Computational Demands of Type Ia SN Simulations Following turbulent nuclear burning requires ~ 1-10 km resolution, whereas radius of star is 10 9 km -- adaptive mesh refinement is therefore essential High-resolution, 3-D, whole star simulations require ~ 100K-300K cpu-hrs on current machines Each simulation ~ 200 MB/cpu-hr; i.e., ~ TB of data We will have used ~ 2M cpu-hrs on DOE ASC machines and ~ 5 M cpu-hrs on DOE Office of Science machines this year; expect to use ~ 50M cpu-hrs next year We will have generated ~ 1 PB of data this year; we expect to generate ~ 3-5 PB of data next year

43 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 x speed-up on BG/P Scaling to 300K-1M cores -- FLASH scales well to 65K cores (BG/L) and we expect the same to 128K cores, but 1M cores? Memory -- astro memory needs are large I/O -- high bandwidth parallel I/O crucial Data transfer Mbytes/cpu-hr generated Data storage -- many Petabytes, must be remote Scientific analysis pipeline -- must be remote Data archive -- Petabytes, must compress

44 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 x speed-up on BG/P Scaling to 300K-1M cores -- FLASH scales well to 65K cores (BG/L) and we expect the same to 128K cores, but 1M cores? Memory -- astro memory needs are large I/O -- high bandwidth parallel I/O crucial Data transfer Mbytes/cpu-hr generated Data storage -- many Petabytes, must be remote Scientific analysis pipeline -- must be remote Data archive -- Petabytes, must compress Astrophysical simulations are often discovery science: the phenomena arevery complicated and highly non-linear; we thereforedon t know all of the questions we want to ask before we see the data, so we must be able to explore it