Most scientist believe universe was created by big bang 13 billion years ago
Universe was a hot glowing ball of radiation in first minutes the nuclei of the lightest elements formed, as universe expanded over milions of years its temp fell, unchares atoms were formed.
A galaxy is a collection of billions of stars held together by there own gravity
Before galaxies and stars formed the universe was a dark patchy cloud of hydrogen and helium, then dust and gas were pullled together by gravitational attraction to form stars. The resulting intense heat in each star started nuclear fusion reacions so they began to emit visible light and other radiation.
The force of gravity pulled matter into galaxies and stars
1 of 6
First part of the life cycle of a star
Gravity pulls the dust and gas together forming a protostar
As the protostar becomes denser the nuclei of hydrogen atoms and other light elements start to fuse
Energy released in the process (fusion) so core gets hotter and brighter
During its 'main sequence' period of its life cycle, a star is stable because the inward force of gravity is balanced by the outward force of radiation.Our Sun is at this stable phase in its life. The star radiates energy due to the fusion of hydrogen in its core. This stage can last for billions of years until the hydrogen runs out
When it runs out of hydrogen nuclei the star swells, cools down, and turns red. Helium and other light elements in its core fuse to form heavier elements.
2 of 6
Life cycle of a star
3 of 6
Low mass star
A low mass star will become a red giant. After fusion stops it will contract to form a white dwarf. Eventually no more light is emitted and the star becomes a black dwarf
4 of 6
A high mass star
A high mass star will swell to become a red supergiant.
After Fusion stops, it collapses and eventually explodes in a supernova.
The outer layers are thrown out into space.
The core is left as a dense neutron star.
If the core is massive enough it becomes a black hole. The gravitational field of a black hole is so strong not even light can escape it.
5 of 6
Formation of chemical elements
Elements as heavy as iron are formed inside stars as a result of nuclear fusion.
Elements heavier than iron are formed in supernovas (along with lighter elements) this is because the fusion process requires the input of energy.
The sun and the rest of the solar system have elements heavier than iron providing evidence that they were formed from debris of a supernova
Comments
No comments have yet been made