A new theory out of the University of Tokyo has an explanation for why some type 1a supernovae appear to have no companion star – the companion star has, over time, become another white dwarf star that is engulfed by the supernova, leaving no trace of its prior existence.
There are two widely held theories about Supernovae creation: the Single Degenerate theory in which a white dwarf accretes mass from its companion star before exploding; and the Double Degenerate theory in which two white dwarf stars join together and then explode.
In some observed supernovae there hasnt been evidence of a companion star to that going nova – normally a red giant or a main sequence star. The new study proposes a reason for this – that the red giant or main sequence star evolves into a faint white dwarf in the mean time as the progenitor star accretes mass.
Typically the progenitor star spins as it accretes mass, taking on the new mass’ angular momentum, increasing its rotation speed and reducing its density below the critical density needed for the star to go nova. The rotation is normally fast enough that the time taken for the spinning star to slow down and the density to rise to criticality is long enough for the companion star to turn into a white dwarf of similar composition to the progenitor star.
This scenario was modelled and found to produce little or no evidence of the companion star compared to the progenitor, which matches observations made of supernovae and some remnants.
The study is available from the Astrophysical Journal Letters, “FINAL FATES OF ROTATING WHITE DWARFS AND THEIR COMPANIONS IN THE SINGLE DEGENERATE MODEL OF TYPE Ia SUPERNOVAE”, Izumi Hachisu, Mariko Kato, and Ken’ichi Nomoto.