The more massive stars burn in turn their hydrogen, their helium, to iron to reach a structure known as in `` onion skin '' (figure 5.6 ) moves towards the branch of super the red giants. The stellar wind peels little by little the layers external of star to make him lose most of its mass. If this stellar wind is sufficiently intense, it can completely peel the layers of hydrogen, even the layers of helium. The star becomes a blue giantess then.
In same time, the
temperature and the pressure of the heart of star did not cease
increasing to reach a few billion degrees and a density close to the
nuclear density (some 
).
To this density, the pressure is primarily carried by degenerated gas
of electrons. When the mass of the heart reaches the mass of
Chandrasekhar, the pressure of the electrons cannot counterbalance any
more the gravitation and the heart starts to break down.
