Type-Ia supernova ( SN-Ia ) explosions are thought to result from a thermonuclear runaway in carbon-oxygen white dwarfs ( WDs ) that approach the Chandrasekhar limit , either through accretion from a companion or a merger with another WD .
However , it is unknown which of these channels operates in reality , and what are the details of the process .
I compile from the literature observational estimates of the fraction \eta of intermediate-mass stars that eventually explode as SNe-Ia , supplement them with several new estimates , and compare them self-consistently .
The estimates are based on five different methods , each utilising some observable related to the SN-Ia rate , combined with assumptions regarding the initial mass function ( IMF ) : the ratio of SN-Ia to core-collapse explosions in star-forming galaxies ; the SN-Ia rate per unit star-formation rate ; the SN-Ia rate per unit stellar mass ; the iron to stellar mass ratio in galaxy clusters ; and the abundance ratios in galaxy clusters .
The five methods indicate that a fraction in the range \eta \approx 2 - 40 \% of all stars with initial masses of 3 - 8 M _ { \odot } ( the progenitors of the WDs generally thought capable of exploding through the above scenarios ) explode as SNe-Ia .
A fraction of \eta \approx 15 \% is consistent with all five methods for a range of plausible IMFs .
Considering also the binarity fraction among such stars , the fraction of binaries with the appropriate mass ratios , the fraction in close initial orbits , and duplicity ( every binary can produce only one SN-Ia explosion ) , this implies that nearly every intermediate-mass close binary ends up as a SN-Ia , or possibly more SNe-Ia than progenitor systems .
Theoretically expected fractions are generally one to two orders of magnitude lower .
The problem could be solved : if all the observational estimates are in error ; or with a “ middle-heavy ” IMF ; or by some mechanism that strongly enhances the efficiency of binary evolution toward SN-Ia explosion ; or by a non-binary origin for SNe-Ia .