Welcome to the Astro Minute, where we’re exploring the universe sixty seconds at a time. I’m Lauren Smyth, and today we’re exploring the death of low- and medium-mass stars.



When a lower-mass star leaves the main sequence, it becomes a red giant in its old age. After a time, the red giant becomes unstable and begins to expand and contract, gently shedding its outer layers. What remains is a white dwarf, a small, hot, extremely dense, mostly carbon core. Though no longer undergoing nuclear fusion, the white dwarf is still hot enough to illuminate its shroud of expelled gas in a colorful display called a planetary nebula. If it has no companion star, the white dwarf will in time cool completely and become a black dwarf. Our own sun will follow this path.



White dwarfs cannot be seen naked eye, but under very dark skies you may see the Dumbbell Nebula, a beautiful planetary nebula.



I’m Lauren Smyth, and that’s your AstroMinute.