Planetary nebula
Stars weighing more than eight solar masses will become supernovae. Stars of lesser mass will form planetary nebulae. After billions of years of stellar evolution a star will have no more hydrogen. This makes the surface of the star colder, and makes the core smaller. The sun's core is about 15 million degrees Kelvin. When it runs out of hydrogen, the smaller core will cause it to rise to about 100 million degrees Kelvin.