Question: how do stars and planets evolve?

Vicky Fawcett answered on 24 Mar 2023:

Great question!

Stars evolve by burning fuel: they start off by burning Hydrogen, which turns into Helium. They then burn Helium which forms more heavy elements and so on. Until they produce Iron, which cannot be burned anymore, so eventually the star will run out of fuel. When this happens it first swells up into a massive “red giant”, and then some massive stars will explode in a supernova. Depending on the size of the star, different star “fossils” are formed, such as a “white dwarf”, “neutron star” or “black hole”.

Planets form from the leftover material that formed stars, but don’t really evolve much once they are formed. Some get smashed into by other planets which might break them up. Eventually they will be destroyed when the host star explodes/dies.