A Model for Type I Supernovae

Abstract

A NUMBER of different mechanisms that could be responsible for Type I supernovae have been suggested1–4 but the problem remains open. Because Type I supernovae are found in elliptical galaxies which are old stellar systems we are faced with finding a mechanism which involves stars of mass ≲ 1 M⊙. I suggest that hydrogen burning caused by mass transfer from a star of 0.7 M⊙−1 M⊙ to a degenerate hydrogen star of mass ∼ 0.1 M⊙ may be responsible. Mass transfer in close binaries is a well established process5,6 and model calculations indicate that the lower mass limit for stars to ignite hydrogen on the main sequence is approximately 0.1 M⊙7–10. The evolution of a 0.1 M⊙ star shows9 that at 1.23 × 109 yr the central temperature is falling while the centre is becoming highly degenerate. If at a later time the star becomes suddenly compressed, raising the temperature of the non-degenerate nuclei enough to ignite hydrogen burning reactions, a thermal runaway occurs. The situation is analogous to the helium flash11 and the carbon-oxygen flash12,13; the latter event may produce a supernova14. The expected rise in central temperature of the degenerate star resulting from compression by the infall. of mass from the primary star can be estimated as follows. The central density ratios of degenerate stars (represented by polytropes of index n = 1.5) with mass ratios (0.1 + ΔM)/0.1 are easily calculated15. Assuming that adiabatic compression, the corresponding central temperature ratios are given by illustration Open image in new window