Modeling type Ia supernovae and quark novae
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odeling Type Ia Supernovae and Quark Novae1 F. K. Röpke Zentrum für Astronomie der Universität Heidelberg, Institut für Theoretische Astrophysik, Philosophenweg 12, D69120 Heidelberg, Germany Heidelberg Institute for Theoretical Studies, SchlossWolfsbrunnenweg 35, D69118 Heidelberg, Germany email: friedrich.roepke@hits.org Abstract—Compact astrophysical objects can change their structure and composition in combustionlike pro cesses. In the case of white dwarfs, thermonuclear burning can even lead to an explosion as a Type la supernova. We give a brief account of the physical concepts of combustion and of methods to model this phenomenon in largescale numerical simulations. As examples for application we discuss thermonuclear explosions of white dwarfs and to hypothetical “quark novae” transforming neutron stars into strange quark stars. DOI: 10.1134/S1063779615050251
1.1 INTRODUCTION: COMBUSTION IN ASTROPHYSICAL COMPACT OBJECTS Combustion is the burning of material in a single reaction or a sequence of reactions that produces heat and leads to the conversion of species. In certain situ ations, this process is restricted to a part of the total volume of the system and it propagates. Then, the phenomenon is called a flame. In contrast to terrestrial combustion, the astrophysical situation usually does not involve chemical reactions but rather results from nuclear physics processes. Thus, an “oxidizer” is not needed and it resembles the case of “premixed” com bustion. Another important distinction of astrophysi cal combustion processes is that they proceed under extreme conditions—densities and temperatures are orders of magnitude higher than in terrestrial systems. Therefore the state of matter is very different and the choice of the appropriate equation of state requires special consideration. Two astrophysical situations that feature combus tionlike processes are the nuclear burning of degener ate white dwarf matter leading to thermonuclear supernovae and the hypothetical burning of hadronic neutron stars into strange quark stars. Although the details of the microphysical conversion and transport processes are very different, a description on large scales (i.e. the numerical simulation of the process involving the entire stellar object) can be achieved by employing the same concepts of flame modeling. Of course, apart from these examples, combustion phe nomena are observed in several other astrophysical objects, such as stars, novae, Xray bursts etc. Thermonuclear burning in carbon/oxygen white dwarf material starts out with the fusion of 12C—a reaction that is extremely sensitive to temperature. In the regime of interest, the corresponding reaction rate 1 The article is published in the original.
scales with ~T 20. Consequently, burning is restricted to a narrow region in space and proceeds in thin fronts, called flames or combustion waves. These possess an internal width on the order of millimetres to centime tres only [1], which is tiny compared to the scales of white dwarf stars. Therefore, it
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