Astrophysical radiative shocks: From modeling to laboratory experiments

Abstract

Radiative shock waves are observed around astronomical objects in a wide variety of environments, for example, they herald the birth of stars and sometimes their death. Such shocks can also be created in the laboratory, for example, by using energetic lasers. In the astronomical case, each observation is unique and almost fixed in time, while shocks produced in the laboratory and by numerical simulations can be reproduced, and investigated in greater detail. The combined study of experimental and computational results, as presented here, becomes a unique and powerful probe to understanding radiative shock physics. Here we show the first experiment on radiative shock performed at the PALS laser facility. The shock is driven by a piston made from plastic and gold in a cell filled with xenon at 0.2 bar. During the first 40 ns of the experiment, we have traced the radiative precursor velocity, that is showing a strong decrease at that stage. Three-dimensional~3D! numerical simulations, including state-of-art opacities, seem to indicate that the slowing down of the precursor is consistent with a radiative loss, induced by a transmission coefficient of about 60% at the walls of the cell. We infer that such 3D radiative effects are governed by the lateral extension of the shock wave, by the value of the opacity, and by the reflection on the walls. Further investigations will be required to quantify the relative importance of each component on the shock properties.

2D numerical study of the radiation influence on shock structure relevant to laboratory astrophysics

“…It can study a wide variety of astrophysical problems ). Furthermore, it was used to develop and analyze a laboratory experiment of radiative shocks (González et al 2006b). This cross-validation between experiment and simulation illustrates the relevance of HERACLES to both laboratory astrophysics and classical astrophysical situations.…”

“…The modeling of these radiative shocks is difficult because of the nonlocal coupling between hydrodynamics and radiation, of the different scales important to radiation and hydrodynamics (Zel'dovich & Raizer 1967;Sincell et al 1999a,b), and of multidimensional effects (Leygnac et al 2006;González et al 2006b). …”

“…The study of radiative shocks on Earth thus require different gases and physical conditions, which can be recreated by high energy installations such as laser or pulsed electric installations (Remington et al 2006). Radiative shock experiments have been performed with high power lasers (Bozier et al 1986(Bozier et al , 2000Keiter et al 2002;Reighard et al 2006;Bouquet et al 2004;González et al 2006b;Busquet et al 2006Busquet et al , 2007. Typically, a 200 J laser in about 1 ns can launch a shock at about 60 km s −1 in targets of millimeter size (Bouquet et al 2004) filled with xenon at pressures of some fractions of bars, whereas supercritical shocks at 100 km s −1 in SiO 2 aerogel, argon, and xenon have been produced at the OMEGA laser (5 kJ).…”

“…Studies of the dynamics of the precursor of xenon radiative shocks by interferometry (Bouquet et al 2004), and shadowgraphy (González et al 2006b), and of its topology by instantaneous X-ray imaging (Vinci et al 2006) indicate that multi-dimensional effects can affect the shock wave, and, in particular, its precursor. This was attributed to the lateral radiation losses (through the walls of the shock tube), which reduce the amount of radiation heating the precursor and thus affect its structure (Leygnac et al 2006;González et al 2006b).…”

“…Studies of the dynamics of the precursor of xenon radiative shocks by interferometry (Bouquet et al 2004), and shadowgraphy (González et al 2006b), and of its topology by instantaneous X-ray imaging (Vinci et al 2006) indicate that multi-dimensional effects can affect the shock wave, and, in particular, its precursor. This was attributed to the lateral radiation losses (through the walls of the shock tube), which reduce the amount of radiation heating the precursor and thus affect its structure (Leygnac et al 2006;González et al 2006b). Keilty et al (2000), Shigemori et al (2000), Edwards et al (2001), Calder et al (2002, and Laming & Grun (2002) focused their studies on the spherical, radiative, blast waves, which are similar to those studied in the previous 1D cases, in terms of the development of radiative precursor, but also exhibit strong differences, such as the importance of radiative cooling and the development of various instabilities.…”