With the advent of high-energy-density (HED) experimental facilities, such as high-energy lasers and fast Z-pinch, pulsed-power facilities, millimeter-scale quantities of matter can be placed in extreme states of density, temperature, and/or velocity. This has enabled the emergence of a new class of experimental science, HED laboratory astrophysics, wherein the properties of matter and the processes that occur under extreme astrophysical conditions can be examined in the laboratory. Areas particularly suitable to this class of experimental astrophysics include the study of opacities relevant to stellar interiors, equations of state relevant to planetary interiors, strong shock-driven nonlinear hydrodynamics and radiative dynamics relevant to supernova explosions and subsequent evolution, protostellar jets and high Mach number flows, radiatively driven molecular clouds and nonlinear photoevaporation front dynamics, and photoionized plasmas relevant to accretion disks around compact objects such as black holes and neutron stars.

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Experimental astrophysics with high power lasers and Z pinches

Rayleigh–Taylor and Richtmyer-Meshkov instability induced flow, turbulence, and mixing. II

Astrophysical research has traditionally been divided into observations and theoretical modeling or a combination of both. A component sometimes missing has been the ability to quantitatively test the observations and models in an experimental setting where the initial and final states are well characterized. Intense lasers are now being used to recreate aspects of astrophysical phenomena in the laboratory, allowing the creation of experimental test beds where observations and models can be quantitatively compared with laboratory data. Experiments are under development at intense laser facilities to test and refine our understanding of phenomena such as supernovae, supernova remnants, gamma-ray bursts, and giant planets.

http://science.sciencemag.org/content/sci/284/5419/1488.full.pdf

Modeling astrophysical phenomena in the laboratory with intense lasers

Spherically symmetric (ID) and two-dimensional (2D) supernova simulations for progenitor stars between 11 M ⊙ and 25 M ⊙ are presented, making use of the PROMETHEUS/VERTEX neutrino-hydrodynamics code, which employs a full spectral treatment of neutrino transport and neutrino-matter interactions with a variable Eddington factor closure of the O(v/c) moments equations of neutrino number, energy, and momentum. Multi-dimensional transport aspects are treated by the "ray-by-ray plus" approximation described in Paper I. We discuss in detail the variation of the supernova evolution with the progenitor models, including one calculation for a 15 M ⊙ progenitor whose iron core is assumed to rotate rigidly with an angular frequency of 0.5 rad s -1 before collapse. We also test the sensitivity of our 2D calculations to the angular grid resolution, the lateral wedge size of the computational domain, and to the perturbations which seed convective instabilities in the post-bounce core. In particular, we do not find any important differences depending on whether random perturbations are included already during core collapse or whether such perturbations are imposed on a ID collapse model shortly after core bounce. Convection below the neutrinosphere sets in 30-40 ms after bounce at a density well above 10 12 g cm -3 in all 2D models, and encompasses a layer of growing mass as time goes on. It leads to a more extended proto-neutron star structure with reduced mean energies of the radiated neutrinos, but accelerated lepton number and energy loss and significantly higher muon and tau neutrino luminosities at times later than about 100ms after bounce. While convection inside the nascent neutron star turns out to be insensitive to our variations of the angular cell and grid size, the convective activity in the neutrino-heated postshock layer gains more strength in better resolved models. We find that low (l = 1, 2) convective modes, which require the use of a full 180 degree grid and are excluded in simulations with smaller angular wedges, can qualitatively change the evolution of a model. In case of an 11.2 M ⊙ star, the lowest-mass progenitor we investigate, a probably rather weak explosion by the convectively supported neutrino-heating mechanism develops after about 150ms post-bounce evolution in a 2D simulation with 180 degrees, whereas the same model with 90 degree wedge fails to explode like all other models. This sensitivity demonstrates the proximity of our 2D calculations to the borderline between success and failure, and stresses the need to strive for simulations in 3D, ultimately without the constraints connected with the axis singularity of a polar coordinate grid.

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Two-dimensional hydrodynamic core-collapse supernova simulations with spectral neutrino transport II. Models for different progenitor stars

We have performed two-dimensional simulations of core collapse supernovae that encompass shock revival by neutrino heating, neutrino-driven convection, explosive nucleosynthesis, the growth of Rayleigh-Taylor instabilities, and the propagation of newly formed metal clumps through the exploding star. A simulation of a type II explosion in a 15 M blue supergiant progenitor is presented, that confirms our earlier type II models and extends their validity to times as late as 5.5 hours after core bounce. We also study a type Ib-like explosion, by simply removing the hydrogen envelope of the progenitor model. This allows for a first comparison of type II and type Ib evolution. We present evidence that the hydrodynamics of core collapse supernovae beyond shock revival diers markedly from the results of simulations that have followed the Rayleigh-Taylor mixing starting from ad hoc energy deposition schemes to initiate the explosion. We find iron group elements to be synthesized in an anisotropic, dense, low-entropy shell that expands with velocities of17 000 km s 1 shortly after shock revival. The growth of Rayleigh-Taylor instabilities at the Si/ Oa nd (C+O)/He composition interfaces of the progenitor, seeded by the flow-structures resulting from neutrino-driven convection, leads to a fragmentation of this shell into metal-rich "clumps". This fragmentation starts already 20 s after core bounce and is complete within the first few minutes of the explosion. During this time the clumps are slowed down by drag, and by the positive pressure gradient in the unstable layers. However, at t 300 s they decouple from the flow and start to propagate ballistically and subsonically through the He core, with the maximum velocities of metals remaining constant at3500 5500 km s 1 . This early "clump decoupling" leads to significantly higher 56 Ni velocities at t= 300 s than in one-dimensional models of the explosion, demonstrating that multi-dimensional eects which are at work within the first minutes, and which have been neglected in previous studies (especially in those which dealt with the mixing in type II supernovae), are crucial. Despite comparably high initial maximum nickel velocities in both our type II and our type Ib-like model, we find that there are large dierences in the final maximum nickel velocities between both cases. In the "type Ib" model the maximum velocities of metals remain frozen in at3500 5500 km s 1 for t 300 s, while in the type II model they drop significantly for t > 1500 s. In the latter case, the massive hydrogen envelope of the progenitor forces the supernova shock to slow down strongly, leaving behind a reverse shock and a dense helium shell (or "wall") below the He/H interface. After penetrating into this dense material the metal-rich clumps possess supersonic speeds, before they are slowed down by drag forces to1200 km s 1 at a time of 20 000 s post-bounce. While, due to this deceleration, the maximum velocities of iron-group elements in SN 1987 A cannot be reproduced in case of the considered 15 M progenitor, the "type Ib" model is in fairly good agreement with observed clump velocities and the amount of mixing inferred for type Ib supernovae. Thus it appears promising for calculations of synthetic spectra and light curves. Furthermore, our simulations indicate that for type Ib explosions the pattern of clump formation in the ejecta is correlated with the structure of the convective pattern prevailing during the shock-revival phase. This might be used to deduce observational constraints for the dynamics during this early phase of the evolution, and the role of neutrino heating in initiating the explosion.

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Non-spherical core collapse supernovae. I. Neutrino-driven convection, Rayleigh-Taylor instabilities, and the formation and propagation of metal clumps

Numerical simulations using the SN hydrodynamics code PROMETHEUS are carried out to study the difference between growth of two-dimensional versus three-dimensional single-mode perturbations at the He-H and O-He interfaces of SN 1987A. We find that in the rest frame of an unperturbed one-dimensional interface, a three-dimensional single-mode perturbation grows ≈30%-35% faster than a two-dimensional single-mode perturbation, when the wavelengths are chosen to give the same linear stage growth in the planar limit. In simulations where we impose single-mode density perturbations in the O layer of the initial model and random velocity perturbations in the postshock fluid near the He-H interface, we find that both axisymmetric O spikes and three-dimensional O spikes penetrate significantly further than two-dimensional O spikes. The difference between two dimensions and three dimensions predicted by our calculations is not enough to account for the difference between observed 56Co velocities in SN 1987A and the results of previous two-dimensional simulations of SN 1987A, but our results suggest that the real three-dimensional hydrodynamics are noticeably different than the two-dimensional simulations predict.

https://iopscience.iop.org/article/10.1086/308220/pdf

Two-dimensional versus three-dimensional supernova hydrodynamic instability growth

Solid-state dynamics experiments at very high pressures and strain rates are becoming possible with high-power laser facilities, albeit over brief intervals of time and spatially small scales. To achieve extreme pressures in the solid state requires that the sample be kept cool, with Tsample 103 GPa (10 Mbar), on the National Ignition Facility (NIF) laser at Lawrence Livermore National Laboratory.

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Materials science under extreme conditions of pressure and strain rate

Supernova (SN) 1987A focused attention on the critical role of hydrodynamic instabilities in the evolution of supernovae. To test the modeling of these instabilities, we are developing laboratory experiments of hydrodynamic mixing under conditions relevant to supernovae. Initial results were reported in J. Kane et al., Astrophys. J.478, L75 (1997) The Nova laser is used to shock two-layer targets, producing Richtmyer-Meshkov (RM) and Rayleigh-Taylor (RT) instabilities at the interfaces between the layers, analogous to instabilities seen at the interfaces of SN 1987A. Because the hydrodynamics in the laser experiments at intermediate times (3-40 ns) and in SN 1987A at intermediate times (5 s-10{sup 4} s) are well described by the Euler equations, the hydrodynamics scale between the two regimes. The experiments are modeled using the hydrodynamics codes HYADES and CALE, and the supernova code PROMETHEUS, thus serving as a benchmark for PROMETHEUS. Results of the experiments and simulations are presented. Analysis of the spike and bubble velocities in the experiment using potential flow theory and a modified Ott thin shell theory is presented. A numerical study of 2D vs. 3D differences in instability growth at the O-He and He-H interface of SN 1987A, and the design for analogous laser experiments are presented. We discuss further work to incorporate more features of the SN in the experiments, including spherical geometry, multiple layers and density gradients. Past and ongoing work in laboratory and laser astrophysics is reviewed, including experimental work on supernova remnants (SNRs). A numerical study of RM instability in SNRs is presented.

https://deepblue.lib.umich.edu/bitstream/handle/2027.42/69672/PHPAEN-6-5-2065-1.pdf?sequence=2&isAllowed=y

Scaling supernova hydrodynamics to the laboratory

Supernova (SN) 1987A focused attention on the critical role of hydrodynamic instabilities in the evolution of supernovae. To test the modeling of these instabilities, we are developing laboratory experiments of hydrodynamic mixing under conditions relevant to supernovae. Initial results were reported by Kane et al. in a recent paper. The Nova laser is used to generate a 10-15 Mbar shock at the interface of a two-layer planar target, which triggers perturbation growth, due to the Richtmeyer-Meshkov instability, and to the Rayleigh-Taylor instability as the interface decelerates. This resembles the hydrodynamics of the He-H interface of a Type II supernova at intermediate times, up to a few times 103 s. The experiment is modeled using the hydrodynamics codes HYADES and CALE, and the supernova code PROMETHEUS. Results of the experiments and simulations are presented. We also present new analysis of the bubble velocity, a study of two-dimensional versus three-dimensional difference in growth at the He-H interface of SN 1987A, and designs for two-dimensional versus three-dimensional hydro experiments.

/pdf/supernova-experiments-on-the-nova-laser-3n2qc95t7n.pdf

G. Bazan

Papers

Two-dimensional versus three-dimensional supernova hydrodynamic instability growth

Materials science under extreme conditions of pressure and strain rate

Scaling supernova hydrodynamics to the laboratory

Supernova Experiments on the Nova Laser