Planetary nebulas are formed when a low to medium mass star runs out of hydrogen fuel in its core. As the star begins to die, it expands into a red giant and eventually sheds its outer layers. The core of the star then heats up and emits ultraviolet radiation, ionizing the surrounding gases and creating the characteristic bright and colorful nebula.
Gravity plays a crucial role in the formation of planetary nebulas. It is responsible for pulling the outer layers of the dying star away, creating the expansive and glowing nebula that we see. Without gravity, the star would simply collapse in on itself without creating the beautiful nebula.
The process of a star becoming a planetary nebula can take anywhere from a few thousand to a few hundred thousand years, depending on the mass of the star. Once the star has shed its outer layers and formed the nebula, it will continue to expand and fade over time until it becomes too faint to see.
Yes, our Sun is expected to become a planetary nebula in about 5 billion years. It is currently in the middle of its life cycle and will eventually run out of hydrogen fuel, expand into a red giant, and form a planetary nebula before becoming a white dwarf.
Planetary nebulas eventually die out due to the dispersal of their gases into the surrounding space. As the gases continue to expand, they become too thin to maintain their glowing appearance. The leftover core of the star, now a white dwarf, will continue to emit radiation but will no longer be surrounded by a nebula.