Rotation does. White dwarfs can exist with mass greater than the Chandrasekhar if they are spun up.I wonder if the rotation of the object has anything to do with it? When a star is rotating rapidly, its centrifugal pseudo-force would have an effect on the pressure on the core, increasing the total mass that the white dwarf can accommodate. The conventional mass of 1.4 I believe is for non-rotating objects.I've also heard that the values were different and unrelated (though I tend to stick with 1.4 for most tests since that's what usually gets the points).So I already talked about this with East and Lumosityfan on IRC earlier and got a good answer, but I'll ask it again because I think it's really interesting:
In a typical CO white dwarf, a type Ia supernova will occur after carbon burning begins due to the runoff nuclear reaction that follows it. But from what I found (Carrol and Ostlie's Introduction to Modern Astrophysics) carbon burning begins at 1.3 solar masses. The "vanilla" explanation (as someone on stackexchange put it) for the type Ia supernova is that it occurs after the Chandrasekhar limit is reached; the value of which is 1.4 solar masses. Comparing these, I suspected that this was a misconception- the type Ia supernova is (at least somewhat) unrelated to the Chandrasekhar limit, and does not need to reach it to explode, although white dwarfs cannot surpass that limit (except in special cases). East and Lumosityfan seemed to confirm this, and the white dwarf does not need to hit the limit; anyone else have input on this?
As for the 1.3, can you explain how fusion makes the white dwarf unstable? In my head, I imagine that fusion would have the effect of decreasing the "load" on the degenerate matter and help prevent collapse.
Most of the times they explode before the Chandrasekhar limit so it is the accepted value but yes detonation is as it approaches the limit, not when it hits it