Stars and their evolution

In short: Stars are huge balls of gas whose cores release energy through nuclear fusion. They form from gas clouds, shine for millions to billions of years and, depending on mass, end as a white dwarf, neutron star or black hole.

In more detail: In the core hydrogen fuses to helium. Radiation pressure balances gravity.

In detail

• Formation: A gas cloud contracts under its own gravity until the core ignites.
• Main sequence: The Sun is a main-sequence star and is about halfway through its life (around 10 billion years in total).
• Red giants: When the hydrogen in the core is used up, the star swells.
• End: Sun-like stars become a white dwarf. Very massive stars explode as supernovae.
• Elements: Almost all heavier elements such as carbon, oxygen and iron were made in stars (sonnensystem, schwarze-loecher-und-neutronensterne).