Stars are a product of gas clouds that collapse under their own gravity. This creates local clumps of gas that become more and more dense and therefore hotter and hotter. When they become hot enough in the centre (>1 mill. °C), the processes of the nucleus turn into a fusion process where hydrogen and hydrogen become helium, just like in a hydrogen bomb.
The violent processes threaten to break up the gas cloud, but its gravity holds it together. If the cloud starts to collapse again, the temperature rises in the nucleus and the nucleus processes increase. This induces the star to grow, resulting in a drop of temperature and the nucleus processes decreasing. Later on in the star’s life, the nucleus temperature will be high enough to fuse helium together and helium to iron.
Oxygen and nitrogen are similarly formed in supernovas. And each time a star enters a new phase - and eventually dies - its gases are spread out into space, where they form the creation of new stars.
This means that stars can actually be called the “gas factories” of the galaxy, which create the heavier elements that form the basis of permanent planets and life, like here on Earth. The next population of stars will therefore include several heavy elements that, during their formation, will be “centrifuged” to a star like the sun, from where the inner planets (Mercury, Venus, Earth & Mars) were created when the solar system was formed 5 billion years ago.
Text: Henrik Rosenørn
Photo: Linde & Astronomibladet (DK)