Formation and Stellar Evolution of a Star

AUTHOR : Tehseen Bukhari

Have you ever wondered how stars came into existence? The first stars were formed after the Big Bang explosion when the universe was about 200 million years old. This led to the vacant universe lightening up with a spectrum of rays.

Our universe is an amalgam of particular elements and dust which eventually formed a “nebula” known as the nursery of stars. The pressure of the gases in the Nebula overcomes mutual gravity, preventing the cloud from collapsing initially; however, gravity eventually overpowers it, and clumps of gases form, gaining mass due to gravity and creating a “protostar”, the core of a clump.

An increase in gravity accelerates the collapse rate. As it collapses, rotation due to “angular momentum” simultaneously takes place, causing the disc to flatten out into a “circumstellar disc” consisting of the inner disc feeding the protostar called “protostellar disc”, and the outer disc called “protoplanetary disk”.

Soon the pressure and the temperature increase, leading to “thermonuclear fusion” in the core where two hydrogen atoms at 10,000 °C temperature combine to form a helium nucleus with the release of energy. Each hydrogen atom has a positive nucleic charge, so they repel each other; therefore, high temperature, pressure, and density are essential for fusion. Fusion takes place till the element Iron, in the core of a star since no more heat energy is gained for further processing.

At the same time, the young star is emitting a strong stellar wind in the form of gas and dust, and some of it is channelled out through the poles. This jet of matter prevents the infall of new mass, and now the baby star becomes a young star since its mass is stable and future evolution set.

“Stellar evolution” is how a star changes over time due to differences in its mass that determines its life cycle. There are two types of stars: small and large stars. The small star has less mass, faster cooling capacity, and a longer lifetime compared to a large star.

When the hydrogen starts to run out, helium becomes abundant, causing helium fusion. The star starts to swell up and becomes hotter, converting into a “ red giant star.” The outer layers of the red giant explode into space, leading to a “planetary nebula.” Eventually, the outer layer of the nebula will disintegrate, leaving behind the core called “white dwarf”, which is extremely hot and cools down over time, contributing its material in the new star formation.

The large stars also swell up and form “red supergiants”; they then collapse and rebound, causing a supernova explosion. Here, the stars on the smaller scale remain as “neutron stars” which are the spinning core leftover, but the larger star forms a “black hole” which sucks up the light that sums up the evolution of stars.

In conclusion, It takes approximately 50 million years for a star formation. The comprehensive life of a star is significantly dependant on its mass, in relation to gravity. Stars came into existence due to elements and dust in the universe that formed into clumps called Protostar (baby star) and due to stellar wind, a solar system was created. Lastly, according to Stellars Evolution, the extent of a star is the Black hole.