Summary
Highlights
The module introduces the topic of the formation of heavy elements. A pre-assessment is conducted to check prior knowledge, covering questions about the Big Bang Theory, light elements, nucleosynthesis, and the most abundant element in space (hydrogen).
The Big Bang theory, accepted as the origin of the universe 13 billion years ago, explains its continuous expansion. Immediately after the Big Bang, protons and neutrons combined to form light elements like hydrogen, helium, lithium, and beryllium through Big Bang nucleosynthesis.
Stellar nucleosynthesis is the process of element formation through nuclear fusion within stars. The life cycle of a star begins as a giant cloud of gas and dust (nebula) that forms into a protostar due to gravity. This develops into a main sequence star where nuclear fusion begins, converting hydrogen to helium.
Main sequence stars evolve into either massive or average stars. Massive stars become red super giants, undergo carbon fusion, and eventually explode as supernovae, dispersing elements into space. Supernovae can leave behind black holes or neutron stars. Average stars become red giants, then white dwarfs, and finally black dwarfs.
Inside stars, various processes create elements: the proton-proton chain reaction (in average stars) converts hydrogen into helium; the CNO (Carbon-Nitrogen-Oxygen) cycle (in massive stars) also converts hydrogen to helium; the tri-alpha process (in red giants) converts three helium-4 atoms into carbon; and the alpha ladder process (in red super giants) creates heavier elements up to iron.
Neutron capture (s-process for slow, r-process for rapid) adds neutrons to atomic nuclei, forming heavier nuclei. Supernova explosions are responsible for creating elements heavier than iron, scattering them across space. The energy emitted during nuclear reactions in stars also manifests as various forms of radiation.