Simulations of astrophysical hydrodynamics: Supernova remnant evolution and star formation.
详细信息
- 作者：Truelove ; John Kelly.
- 学历：Doctor
- 年：1997
- 导师：McKee, Christopher F.
- 毕业院校：University of California
- 专业：Physics, Astronomy and Astrophysics.;Computer Science.
- ISBN：0591794829
- CBH：9827126
- Country：USA
- 语种：English
- FileSize：7971269
- Pages：276
文摘
Many problems in astrophysical hydrodynamics are analytically intractable. In such cases, numerical simulation can provide valuable insight into the nature of the solution. We consider two such problems: the interaction of stellar ejecta and ambient gas in an evolving supernova remnant (SNR), and the collapse and fragmentation of molecular clouds to form stars.;We first study the dynamics of SNR evolution from the ejecta-dominated stage through the Sedov-Taylor stage, the stages which precede the onset of dynamically significant radiative losses. We emphasize that all nonradiative SNRs of a given power-law structure evolve according to a unified solution, and we discuss this general property in detail. We present 1-D numerical simulations of the flow and use these to aid the development of approximate analytic solutions for the motions of the SNR shocks. We elucidate the dependence of the evolution on the ejecta power-law index n by developing a general trajectory for all n and explaining its relation to the solutions of Chevalier (1982) & Nadyozhin (1985) for $n > 5$ and Hamilton & Sarazin (1984) for $n = 0.$ These solutions should be valuable in describing relatively young SNRs at intermediate points of nonradiative evolution.;We then turn to 3-D simulation of star formation using adaptive mesh refinement (AMR). We demonstrate that perturbations arising from discretization of the equations of self-gravitational hydrodynamics can grow into artificial fragments. This can be avoided by ensuring the ratio of cell size to Jeans length, which we call the Jeans number, $J \equiv\Delta x/\lambda\sb{J},$ is kept below 0.25. We refer to the constraint that $\lambda\sb{J}$ be resolved as the Jeans condition. We find that it is not possible a priori to have confidence that results of calculations which employ artificial viscosity to halt collapse are relevant to the astrophysical problem.;Finally, we describe our new AMR code in detail. This code employs multiple grids at multiple levels of resolution and dynamically configures them to maintain adequate resolution. Since fragments involving large dynamic ranges in length scale can form at unpredictable locations, this adaptivity is crucial. We present illustrative applications employing the Jeans condition and set new benchmarks on each problem we consider. We find that the uniformly rotating, spherical clouds treated here first collapse to disks in the equatorial plane and then, in the presence of applied perturbations, form filamentary singularities that do not fragment while isothermal. Our results provide numerical confirmation of recent work by Inutsuka & Miyama (1992, 1997).