• Every star has a life cycle: a beginning, a middle and an end. At the beginning, a star forms from a massive cloud of gases and dust called a nebula (gases include hydrogen and helium).
• The gravitational forces begin to pull the gas and dust particles close together, creating clumps. The clumps become more massive and gravity becomes even stronger. Over time, a dense region forms, called the protostar.
• Gravity causes the core of the protostar to become very tightly packed and the pressure causes nuclear fusion to begin. Hydrogen atoms in the core fuse to make helium atoms and as a consequence, produce tremendous amounts of energy.• Billions of years after forming, the star begins to burn out.
Stars like the Sun• For about 10 billion years, a star’s available hydrogen will have been converted to helium. With less hydrogen to burn, the core begins to contract and gets hotter, while the outer layers of the star expand and then cool. The star evolves into a red giant. Our sun will become a red giant in 5 billion years. The outer layers of the star drift off and leave a small, dim hot core behind – a white dwarf.
More massive stars• Stars that are more massive than our Sun (i.e. 10 times more larger) will become a red supergiant. Once fusion stops, the supergiant will have its contents collapse on its self under its own gravity. The outer layers of the star explode outwards – known as a supernova.
Supernova • All the atoms we are made from came originally from these giant supernova explosions.
If a star’s initial mass was:• between 10 and 30 solar masses a neutron star is formed – an extremely dense star composed of tightly packed neutrons.• greater than 30 solar masses black hole is formed – a quantity of matter so dense and gravity so strong that not even light can escape.