Astrophysical environments can be characterized by extremes of temperature and density. Under such conditions, thermonuclear or pycnonuclear ignition of the available nuclear fuels can yield explosive release of energy in the form of a nuclear "flash." Three classes of events of this nature are being studied at the Flash Center. The accretion of hydrogen-rich matter onto the surface of a white dwarf in a binary stellar system yields hydrogen ignition conditions - that is, conditions for which the pressure is relatively insensitive to the temperature. A violent hydrogen thermonuclear "runaway" ensues: a "classical nova" event. In a similar manner, the accumulation of a helium layer on the surface of a neutron star can result in a helium thermonuclear runaway: an "X-ray burst." On an even more impressive scale, the ignition of carbon fuel in the deep interior of a white dwarf at the Chandrasekhar limit can yield a Type Ia supernova event, the power output of which can rival that of the entire galaxy in which the explosion occurs.
The Astrophysics Group is carrying out hydrodynamic simulations of the explosion phase of Type Ia (thermonuclear-powered) and Type Ib/c and Type II (core collapse) supernovae. The simulations led to the discovery of an entirely new explosion mechanism for Type Ia supernovae called the gravitationally confined detonation model. The group is validating current models of these explosions against observations by calculating the light curves and spectra predicted by the simulations and confronting them with observations. The group also studies key physical processes in these events.