I know that, in trillions of years, all Ia supernovae will be binary white dwarfs spiralling together, but what is the proportion viv-a-vis WD accreting off a "normal" companion 13.7 gigayears after the Big Bang? One scenario has a 1 solar mass WD going to a 2 solar mass WD and going BOOM, another has a 1.39999999 solar mass WD going to 1.40000001 solar masses and going BOOM. Can these be distinguished? How about seeing progenitors? Does the accreting WD give of X-rays, for example?
Any idea on which model is currently predominant?