How stellar corpses are made
1 Main sequence
A star burns hydrogen during this phase, which lasts most of its life.
2 Red giant
Once hydrogen burning stops and helium burning starts, the star bloats.
3 Planetary nebula
Helium burning is unstable, and eventually the star sheds its outer layers into space.
4 White dwarf
A core of carbon and oxygen – the products of helium burning – is left behind.
“They get closer and closer until they suddenly crash into each other, sparking another supernova”