Signatures of Shocks and Particle Acceleration from Novae in our Galaxy

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1. A nova eruption is a dramatic increase in energy output caused by runaway thermonuclear burning of hydrogen on the surface of a white dwarf star. Ordinarily, a white dwarf (a star with the mass of our Sun crammed into a volume about the size of the Earth) contains little or no hydrogen. If it has an ordinary star as a companion, however, a white dwarf can sometimes accumulate hydrogen from the companion onto its surface. As little as a few ten-thousandths of the mass of our Sun can be enough to trigger the thermonuclear "burning" of this hydrogen fuel. Runaway hydrogen burning produces the observed nova outburst and violently ejects mass from the white dwarf. Recent spacecraft observations have revealed gamma-ray emission during nova outbursts. These observations demonstrate that hydrodynamic shocks occur in novae. This research aims to use computer simulations to study the origin, appearance, and implications of these shocks. The work will greatly improve the understanding of emission at many different wavelengths during nova outbursts. It will also improve scientists? understanding of the acceleration of ions and electrons to extremely high energies. The Intellectual Merit of the work comes from such advances. The involvement of undergraduate students in the research and public outreach through movies and an interactive website are good Broader Impacts of the research.2. Novae are sudden outbursts of energy powered by runaway thermonuclear burning on the surface of a white dwarf that has accreted matter from a stellar companion. The recent discovery of GeV gamma rays emitted during nova outbursts provides a striking indicator that hydrodynamic shocks occur in these systems. This project will employ hydrodynamic calculations to study the origin, appearance, and implications of shocks in novae. The work will also investigate the efficiency of shock acceleration of electrons and ions as well as magnetic-field amplification at the shock. In addition, the combination of numerical simulations and multi-wavelength modelling will be used to constrain various shock parameters. The Intellectual Merit of the research derives from improved understanding of emission from novae and of a mechanism of particle acceleration in astrophysics. The results will also inform both radio and optical surveys for transient phenomena. The Broader Impacts of the work will involve not only research opportunities for undergraduates but also public outreach through an interactive website, color movies, and a workshop for high school teachers.