Massive stars undergo a normal life; they
fuse hydrogen into helium, then helium
into oxygen & carbon, then oxygen
into silicon & sulfur and finally into IRON.
Therefore, they have the power to fuse
helium into other elements unlike the less
massive stars. The materials of this explosion spread in the cosmos forming
moons, new stars, and planets including Earth. This is where almost 93% of the elements of human body came from as well. By means, we are essentially made of stardust.
Afterwards, the system collapses and the universe is showered with heavy elements. The gravity attempts to crash the left core, but first it has to overcome the electron degeneracy pressure.
The next stage depends on the star's remaining mass:
If the star's remaining mass is between 1 1/2 to 3 times the mass of the Sun, it will collapse into a neutron star
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If the star's remaining mass is greater than three times the mass of the Sun, the star contracts tremendously and becomes a black hole
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"The nitrogen in our DNA, the calcium in our teeth, the iron in our blood, the carbon in our apple pies were made in the interiors of collapsing stars. We are made of starstuff."
Carl Sagan, Cosmos