Two dwarf white: doubly degenerated system

The arguments in favour of the doubly degenerated systems are the natural absence of hydrogen and helium and a relatively simple approach to reach the mass of Chandrasekhar (if the sum of the masses is higher than $M_{ch}$). The existence of such objects is proven, but their period of rotation one half-year or more implies lifespans of the order of the time of Hubble (the two stars approach by emission gravitational waves). Lastly, they have masses which reach with more the one solar mass, well below the mass of Chandrasekhar. Moreover, it is rather difficult to explain the homogeneity of the supernovæ of the Ia type in this model, the two components being able to have very variable characteristics as for their mass or their composition.