Stars are the stuff of our dreams. They twinkle at night, shining brightly in the dark, night sky. But stars too have a life span. They are born, they have a life and they die but their death is not the end; it is the beginning of something new. However our human life is not enough to see the life, let alone the beautiful process of the birth of a star.
Birth of a Star
Stars are born in something called a Nebula. Nebulas/ nebulae are cold, dense, dark clouds of gas and dust and are a nursery of stars. These nebulas have a high density and a very low temperature. These clouds want to dissipate or spread out but the gravity that surrounds this cloud keeps it from spreading out into the atmosphere. In this way a sort of tug of war begins between the gas cloud and the gravity that surrounds it. A balance is created between the gravity pulling in and the gas pushing out.
Finally, gravity wins and the gas gets crunched into a giant spinning disk which is bigger than our entire solar system. This is the beginning of the formation of a star. As gravity keeps on pushing the gas inward and compresses the disk, this disk becomes denser and hotter. It gets so hot due to the pressure of gravity pushing in, that huge jets of gas burst out from the center of the disk. These jets of gas are many, many lightyears long. Gravity pulls more and more gas to the centre of the disk. The gas and dust particles smash into each other generating more and more heat, resulting in a more dense and hotter disk and continues this way until this disk becomes smaller, brighter and hotter. And thus a star is born. This young star reaches very high temperatures of 15 to 18 million degrees. This young star is called a protostar.
The next stage in the life of a star is called the Main Sequence stage which is the stage where nuclear fusion starts to take place.
Nuclear fusion is the process used by stars to generate energy. It is the reason stars shine. Nuclear fusion is a process in which Hydrogen atoms fuse together to form Helium. This process produces a great amount of energy which is radiated out into space and thus a star begins to shine. This is known as the main sequence stage in the life of a star.
This energy produced by the core of a star creates a force called the thermonuclear force that pushes away in the opposite direction of the core, that is, towards the outside of the star. However, the gravity pushing inward doesn’t allow the atoms of the star to spread out away from the core. These two forces maintain the balance of the star.
There are many different kinds of stars such as the red dwarf which is the smallest type of star and most stars can be categorized as red dwarfs. Proxima Centauri which is the closest star to the sun is a red dwarf. A yellow star is a bigger star. The Sun is an example of a yellow star. There are also red stars and blue stars. Blue stars are the biggest stars and the hottest stars in the universe. However, all these stars are powered by the same process of nuclear fusion. The only difference is the speed at which hydrogen atoms fuse. In smaller stars hydrogen is burned much slower as compared to bigger stars thus having a much longer life than that of the blue giants.
Larger stars, after depleting their hydrogen resources, start to fuse helium atoms into heavier elements like Carbon and Oxygen. These stars even go to the extent of fusing elements all the way up to Iron beyond which point the elements can no more fuse. As this process takes place, it creates more energy and causes the outer layer of the star to expand thus becoming a super red giant. Betelgeuse is a super red giant.
Death of a Star
When the hydrogen atoms in a star are depleted or over, that is the beginning of the end for the star. The star now begins to die.
Medium stars after burning its fuel expand into red giants as the outer layer of the star starts going farther and farther away from the middle of the star. When the fuel in the core of the star is exhausted it will lose its outer layer as it sheds is atoms forming a planetary nebula and will shrink and become a white dwarf. The white dwarf is the core of the star which is very dense and very hot; however, its mass is much less that the original mass of the star. It is of the size similar to that of the earth. This white dwarf, over the course of a few million years will slowly cool down. It will stop shining completely and become a black dwarf.
A larger star on the other hand, becomes a super red giant before collapsing in on itself. This causes a massive explosion called a supernova. A supernova can outshine all the stars in the galaxy. Either the star survives the explosion and transforms into a neutron star or it becomes a black hole.