Question

All stars go through a lifecycle.

Answer 1

Mira is much bigger than the Sun.

Only very massive stars will go through a supernova stage, causing the outer layer to explode away and the core to collapse in on itself, becoming very dense.

Answer 2

As the nuclear fusion within the core of Mira loses fuel the force pushing in on the core start to overwhelm the outward force. as this happens the star core becomes dense starts to fuse nuclei into heavier elements. once the star reaches iron, there is nothing left to fuse and the outward force suddenly gives way, therefore the gravitational force suddenly pulls the outer layers toward the center at high speeds, but once it is condensed against the iron core, the outer part essentially bounces off the iron core, shooting the outer layer of the star out into space in an explosion known as a supernova. our sun however, does not have enough pressure to fuse nuclei into iron. this means that the outward force of the star will actually be able to compensate for the gravitational force and as the star runs out of fuel, the star will compress and become denser fusing more nuclei, therefore pushing out with more force than the gravitational is pushing in. this means that instead if the star collapsing on itself it will grow until it uses up all its fuel, before it will slowly shrink until it completely dies out