The progenitors of type Ia supernova

Type la supernovae are identified as exploding degenerate stars. Their luminosity is due to the radioactive decay of about a solar mass of Ni-56 through Co-56 to Fe-56. As such they are a major source of iron in the inter-stellar medium. Although it is generally accepted that a degenerate carbon/oxygen white dwarf explodes as it accretes material from a binary companion, the progenitors of type la supernovae have not been categorically identified. We discuss the various possible progenitors in detail and indicate theoretical and observational difficulties with each possibility. It may well be that, the true nature of the progenitors has not yet even been conceived of. We look at why population synthesis fails to help distinguish and consider how the advent of population nucleosynthesis may change this. When used as universal standard candles SNe la are calibrated with the Phillips relation between absolute luminosity and light curve shape. This must therefore be valid at all redshifts and so both the absolute luminosity and the light curve decal, must only depend on a single major property of the progenitors. We report on the latest understanding of this relation and find little to justify its universality beyond the local empirical evidence. A major effect on the absolute luminosities is the neutron to proton ratio at the time of the explosion because this determines the fraction of iron group elements made up of Ni-56.