ASC / Alliances Center
![[ASC Logo]](/website/common/img/newlogo.png)
Research in the Astrophysics Group is focused upon studies of thermonuclear flashes, relevant to a rather diverse array of problems currently challenging researchers in theoretical nuclear astrophysics. These include hydrogen flashes on white dwarfs (novae), helium flashes on neutron stars (X-ray bursts), and carbon flashes in white dwarfs (Type Ia supernovae). This Group is also concerned with the physics and astrophysics modules for the FLASH code, and has led in the development of the equation of state and nuclear burning modules currently in use.
Group Leader: Jim Truran.
Description of the Astrophysics Group Research
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 under ‘degenerate’ 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.
Existing theoretical models of these various astrophysical thermonuclear flashes fail to reproduce many detailed observational features of their outbursts. For example, none of the several competing mechanisms for the Type Ia supernovae explosions provides a clear and unambiguous explanation for the observed behaviors of supernova light curves. We seek to understand these behaviors, which permit the use of SN Ia light curves to determine cosmological distances and constrain fundamental cosmological constants. Similar challenges face studies of novae and X-ray bursts.
The Astrophysics Group at the FLASH Center intends to study novae, supernovae Type Ia, and X-ray bursts using hydrodynamical simulations. Members of the astrophysics group have played a significant role in the development and testing of the FLASH code, and are currently using it to address these problems.
