Most scientists believe the universe was created by a 'Big Bang' about 13 billion years ago
At first the universe was a hot glowing ball of radiation. In the first few minutes, the nuclei of the lightest elements formed. As it expanded, over millions of years, its temperature fell. Uncharged atoms were formed
Eventually dust and gas were pullet together by gravitational attraction to form stars. The immense heat started nuclear fusion in the stars, so visible light was emitted.
Gravitational forces increased as the stars increased in size, and dusts and matter was attracted to them, and this may have been how planets formed
Large groups of stars are called galaxies. The sun is one of the many billions of stars in the Milky Way galaxy. There are billions of galaxies in the universe
Life History of a star
Stars form from clouds of dust and gas
- Gravitational forces make the clouds become very dense, forming a Protostar
- As it becomes more dense, it gets hotter which leads to the nuclei of the hydrogen atoms fusing together
- Energy is released here and so the core gets hotter and brighter, and the star begins to shine
Nuclear fusion can continue in a star for billions of years until the hydrogen nuclei run out
In a star, the inward force of gravity is balanced by the outward pressure of radiation from the core. The star is therefore stable. During this stable period the star is called a 'main sequence star'
When a star runs out of hydrogen nuclei its swells into a 'red giant', it is red because the surface has cooled
The next stage depends on its size, a star similar to out sun will contract to form a white dwarf, and eventually no more light is emitted and it become a black dwarf (not a black hole)
A star much larger than the sun will continue to collapse and explode into a 'supernova'. If massive enough it will become a 'black hole'
Life of a star
Low mass star:
Protostar > Main stage sequence > Red giant > White Dwarf > Black Dwarf
High Mass Star:
Prostar > Main Stage sequence > Red Giant > White Dwarf > Supernova > Black hole
A black hole will develop if the star is massive enough. The gravitational field of a black hole is so strong that not even light can escape
How the chemical elements are formed
Chemical elements are formed by nuclear fusion in stars.
The nuclei of lighter elements fuse together to form the nuclei of heavier elements
For elements heavier than iron to be formed there must be an input of energy