Nebulosa

The term 'nebulae' was initially used for objects that appeared fuzzier than stars. Many of these were later identified as galaxies. Nebulae form in different ways, such as from the remnants of exploded stars, dimming small stars, or interstellar gas held by gravity.

What happens to stars that explode or simply dim?

What is the role of gravity in the formation of nebulae from interstellar gas?