Complex sentence: This may happen when the core of a white dwarf star above the vicinity of 1.4 solar masses, the Chandrasekhar limit, collapses and is not halted by the degenerate electrons, or more typically when the core of a massive star collapses.
Split into simpler sentences: This may happen when the core of a white dwarf star is above the vicinity of 1.4 solar masses, which is the Chandrasekhar limit. The core collapses and is not halted by the degenerate electrons, or more typically when the core of a massive star collapses.