New Superburst Theory

When a neutron star pulls matter from a nearby companion onto itself, powerful x-ray bursts, visible to telescopes in Earth orbit, can result. Some astronomers believe the bursts leave behind an ocean of debris, heavy nuclei mostly, on the neutron star's surface.
Occasionally much larger "superbursts," with up to 1000 times the amount of x rays than other bursts, can flare up. Henrik Schatz of Michigan State University (517-333-6397) and his collaborators Lars Bildsten from UCSB and Andrew Cumming of UCSC believe that an energy blitz is generated when high energy photons strike the heavy nuclei in the debris ocean, springing free either a proton, neutron, or alpha particle, which then recombine with the residual nuclei forming lighter, stronger bound nuclei and free energy. This photodisintegration process is triggered by the thermonuclear explosion of a small amount of carbon, but may then proceed subject to positive feedback: the warmer the surface temperature the more disintegration, which in turn leads to warmer temperatures. The runaway production of energy through the conversion of heavy nuclei into lighter nuclei could be unique in astrophysics: all other thermonuclear energy generation (such as those inside our sun) proceeds by fusing lighter nuclei into heavier nuclei. (Schatz et al., Astrophysical Journal Letters, 3 January 2003; see also http://groups.nscl.msu.edu/nero/)