Medium mass stars have a complex evolution. In the first phases they evolve in the same way as low mass stars.

When the helium core is exhausted the stellar collapse occurs and the outer layers reignite. Then, the outer shell of hydrogen burning, the inner shell of helium burning and the core would be shown.

In this moment the Carbon supply is exhausted. Several layers transform into others, for example the helium shell becomes a carbon one. At this point in the life of the star the last fusion (the one that produces less energy) is the one of chromium into iron. During these final stages the star expands becoming a red supergiant.

Finally there is a problem; the star hasn’t got enough energy nor to separate neither to fuse elements. As a result the pressure that supported the star disappears and the star undergoes a gravitational collapse.

After the collapse the star becomes a neutron star because the protons and electrons in the core are compressed into a ball of neutrons. A pulsar is a neutron star that produces electromagnetic emissions.

 In the last moments of a medium mass star’s life it collapses becoming a supernovae. Then it is able to fuse elements like gold and uranium, rapidly ejects them to the outer space together with huge amounts of energy.

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