Topics of Interest Astronomy (Stars, Galaxies And Beyond )
Raj Kumar Parashari 05 Aug, 2020 Views: 218
All of us are made up of elements such as hydrogen, carbon, nitrogen, oxygen, calcium, iron, phosphorus, zinc etc. If we look around extensively, then we will find that there exist heavy elements such as Gold, Silver, Palladium, Platinum, Thorium, radium …….
There are several mythologies citing the creation of universe. Where from these elements came? It has been a challenging question since several decades. Scientists haves been in pursuit of finding answer to these questions and have unlocked a few mysteries for us. Answer to these lies in the life cycle of a star.
Immediately after the big bang space expanded quickly and cooled down forming huge clouds of hydrogen called as nebulae. Nebulae are the breading ground of stars. It is where large clouds of hydrogen from a rotating solid spherical ball called as Proto -star.
Proto- stars have tendency to collapse under gravity. In the process the temperature at the centre keep rising. When it grows to about 107 K the nuclear fusion starts generating huge amount of energy and outwards pressure. So produced energy comes on the surface and proto star starts glowing. The Star is born!! Outward pressure does not allow star to collapse further.
Light stars (lighter than Sun) stay in its main sequence longest and appear to stay forever (their life span is more than age of the universe which is about 14 billion years).
The beginning of death of a star like Sun begins when almost all of its fuel around the core changes to helium. Outward energy pressure exceeds the inward gravitational pressure of leftover outer shell and thus the Star starts swelling. Sun will swell so large that it will engulf planets Mercury, Venus and even Earth. Its temperature also drops and appear red and hence called as Red Giant Star. In time it will shed its thin outer layer and interplanetary dust. Finally, left over core is much smaller in size and glows due to fusion of helium in to carbon. Now it is called as the white dwarf star. When all of its helium is converted in to carbon. It will stop glowing and will stay forever where it is.
For the case of stars which are much heavier than Sun, as these turns to super red giant phase its core keep collapsing under gravity producing heavier and heavier elements till iron is formed. Nuclear fusion within the core stops and due to lack of outward energy pressure, outer shell falls in to the core with extremely high speed and then star explodes as supernova explosion and finally end up as a neutron star or a black whole depending upon mass of the leftover core.
Raj Kumar Parashari
Jayshree Periwal High school