Planetary Nebulae

When a red giant exhausts its helium fuel, it cannot ignite the next element (carbon) because its core is not massive enough. The outer layers drift away into space, forming a beautiful planetary nebula — a glowing shell of gas illuminated by the hot core. These nebulae last only about 10,000 years before fading.

The exposed core left behind is a white dwarf — roughly Earth-sized but incredibly dense. A teaspoon of white dwarf material would weigh about 5 tons. The white dwarf slowly cools over immense timescales; in the far future it should become a cold, dark black dwarf, but the universe is not old enough for any black dwarfs to exist yet.