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Title: When shock waves collide

Supersonic outflows from objects as varied as stellar jets, massive stars, and novae often exhibit multiple shock waves that overlap one another. When the intersection angle between two shock waves exceeds a critical value, the system reconfigures its geometry to create a normal shock known as a Mach stem where the shocks meet. Mach stems are important for interpreting emission-line images of shocked gas because a normal shock produces higher postshock temperatures, and therefore a higher-excitation spectrum than does an oblique shock. In this paper, we summarize the results of a series of numerical simulations and laboratory experiments designed to quantify how Mach stems behave in supersonic plasmas that are the norm in astrophysical flows. The experiments test analytical predictions for critical angles where Mach stems should form, and quantify how Mach stems grow and decay as intersection angles between the incident shock and a surface change. While small Mach stems are destroyed by surface irregularities and subcritical angles, larger ones persist in these situations and can regrow if the intersection angle changes to become more favorable. Furthermore, the experimental and numerical results show that although Mach stems occur only over a limited range of intersection angles and size scales,more » within these ranges they are relatively robust, and hence are a viable explanation for variable bright knots observed in Hubble Space Telescope images at the intersections of some bow shocks in stellar jets.« less
Authors:
 [1] ;  [2] ;  [3] ;  [3] ;  [4] ;  [2] ;  [5] ;  [5] ;  [4] ;  [6] ;  [5] ;  [7] ;  [6]
  1. Lawrence Livermore National Lab. (LLNL), Livermore, CA (United States)
  2. Rice Univ., Houston, TX (United States)
  3. Univ. of Rochester, Rochester, NY (United States)
  4. Los Alamos National Lab. (LANL), Los Alamos, NM (United States)
  5. AWE, Aldermaston, Reading Berkshire (United Kingdom)
  6. General Atomics, San Diego, CA (United States)
  7. Sandia National Lab. (SNL-CA), Livermore, CA (United States)
Publication Date:
OSTI Identifier:
1289387
Report Number(s):
LLNL-JRNL-698500; LA-UR-15-24971
Journal ID: ISSN 1538-4357
Grant/Contract Number:
AC52-07NA27344; NA0001944; NA0002037; NA0002722
Type:
Accepted Manuscript
Journal Name:
The Astrophysical Journal (Online)
Additional Journal Information:
Journal Name: The Astrophysical Journal (Online); Journal Volume: 823; Journal Issue: 2; Journal ID: ISSN 1538-4357
Publisher:
Institute of Physics (IOP)
Research Org:
Lawrence Livermore National Lab. (LLNL), Livermore, CA (United States); Los Alamos National Lab. (LANL), Los Alamos, NM (United States); Sandia National Lab. (SNL-CA), Livermore, CA (United States)
Sponsoring Org:
USDOE National Nuclear Security Administration (NNSA)
Contributing Orgs:
Rice Univ., Houston, TX (United States); Atomic Weapons Establishment (AWE), Berkshire (United Kingdom); Univ. of Rochester, NY (United States); General Atomics, San Diego, CA (United States)
Country of Publication:
United States
Language:
English
Subject:
42 ENGINEERING; 79 ASTRONOMY AND ASTROPHYSICS; Herbig-Haro objects; hydrodynamics; ISM: jets and outflows; methods: laboratory: atomic; shock waves; stars: jets; Herbig–Haro objects; jets and outflows; atomic laboratory methods; stars; jets