THE Death of a star
When a star runs out of hydrogen, fusion stops, and it can no longer hold itself up against gravity. At this point, the star tries to reproduce energy.
Not only the mass of the star affects how long it will live, but also how it will die. So at this stage different star masses will die differently.
The death of low mass stars
(Low mass means less than about 8 times the mass of the Sun) Now, the star ran out of hydrogen. And In order to burn the helium inside the star again, its core needs to be 10 times hotter than it used to be during its lifespan. This is achieved by the gravity attempts to crash the star.
So, gravity is pulling the matter more and more together. The core gets extremely hot and dense. The star fuses helium and tries to fuse carbon, but does not succeed. At this point, the outer atmosphere of the star cannot be held by gravity that it starts to evaporate away ejecting glowing shells of ionized gasses illuminated by the hot central star, which is known as the planetary nebulae phenomenon.
i.e. As the center of the star cannot sustain carbon fusion process, gravity takes over the star. And what is left is the core of the star that becomes a "white dwarf".
All of these actions happen in the last 10% of a star life.