Here's why:
* Low-mass stars have a relatively slow nuclear fusion process, which means they live longer than high-mass stars.
* As they age, low-mass stars expand into red giants, eventually shedding their outer layers into space.
* This ejected material forms a glowing shell around the star, called a planetary nebula.
* The remaining core of the star, a white dwarf, slowly cools down over billions of years.
High-mass stars, on the other hand, undergo a much more dramatic end. They explode as supernovas, leaving behind either neutron stars or black holes.
Therefore, planetary nebulae are a product of the final stages of low-mass stars, not high-mass stars.
