Wonder - A Scientific Oratorio
A bright supernova explosion can be seen at lower left of this galaxy (SN 1994d in galaxy NGC 4526).
Credit:NASA/ESA, The Hubble Key Project Team, and The High-Z Supernova Search Team.
Theme 5 - The death of stars
Stars draw their energy from giant nuclear fusion reactors at their cores. Here the chemical elements heavier than hydrogen and helium are made and when the star runs out of fuel, it scatters these elements into space forming the raw material for the next generation of stars.
When stars form from clouds of gas they range in mass from maybe a tenth that of the Sun to a hundred times or more. Inside each star is a nuclear furnace which at first draws its energy from fusing hydrogen into helium. Eventually the star will run out of hydrogen fuel. For the Sun this will happen in about 5 billion years. For the most massive stars this can happen in only a few million years.
When the hydrogen fuel is exhausted the core of the star collapses under its own weight, creating more extreme conditions in which helium can be used as the fuel to create elements like carbon, nitrogen and oxygen. For the most massive stars this cycle is repeated, with successive cycles of nuclear fusion gradually building the heavier and heavier elements.
A star like the Sun never uses any fuel heavier than helium. Expanding to become a red giant which will probably engulf the Earth, the Sun will die in about 5 billion years and its outer layers will be spread into space leaving behind its core as a dead white dwarf star about the size of the Earth.
The story is even more dramatic for the more massive stars. Eventually when the core of a massive star is composed of iron and nickel, it can gain no more energy from fusion. The core collapses in less than a second creating a super-dense neutron star (a dead star weighing as much as the Sun but only the size of a city) or even a black hole. The rest of the star is blasted into space in a titanic supernova explosion. In the explosion even heavier elements are created, such as gold and uranium.
All these elements are then spread into space to form the raw materials from which the next generation of stars may form. This cycle has been repeated many times during the history of the Universe and continues today. Almost everything you see around you now - the elements from which your body is made, every single atom of oxygen you breathe - was made billions of years ago, inside a star.
