Introduction – Stars

Stars in the Sky
Stars in the Sky

When we look up at the night sky, we see a few small flickering sources of light. These are the stars. They are beautiful aren’t they? But it is hard to imagine that these small flickering lights are actually the largest thermonuclear bombs in the universe!

Stars are huge balls of gas and plasma. The nearest star to us is the sun. The sun is the reason that all life on Earth as we know, exists. But how is a ball of gas the biggest thermonuclear bomb in the universe? Let’s see…

Formation of a Star

Stars form in enormous clouds of dust and hydrogen called nebulae. As the dust and hydrogen are not uniformly spread in the nebula, there are a few regions with more mass compared to others. Regions with high density of hydrogen start pulling the surrounding hydrogen towards itself due to the force of gravity. When the cloud of collected hydrogen gets big enough, the cloud starts to collapse under the influence of its own gravity. This process heats up the center and after a million years when the temperature is high enough, fusion starts taking place. The energy released by this fusion opposes the force and gravity and stabilizes the cloud and a star is born. The star shines as a small part energy released during fusion is in the form of visible light. The energy released by a fusion in a star is equal to thousands of hydrogen bombs exploding every second!

Death of a Star

A star does not collapse under its own gravity because there is a delicate balance between the force and gravity and the energy released by fusion. Over a course of millions or billions of years (depends on size of star), a star converts almost all of its nuclear fuel (hydrogen) into helium. The balance is disturbed and gravity takes over. Under the influence of gravity, the core starts to shrink, therefore heating it up. The outer layers of the star start to expand continuously and the star becomes a red giant. The story after this depends on the mass of the star…

If the star is medium sized like our sun, the star will continue to live on its red giant status for a few billion years and then all the layers of the star will expand farther and farther away from the core into space

Creating a planetary nebula and leaving behind a dense, Earth sized core called a white dwarf.

The case of larger stars is violent. Large stars can further fuse helium into carbon then oxygen then neon then silicon and finally iron. The fusion of heavy atoms of iron does not release enough energy to keep the star stable. As a result the star collapses in a second under its own weight and the outer layers are thrown into space at a fraction of the speed of light. This is called a Supernova. They are perhaps one of the most powerful and amazing explosions in the universe. This event leaves behind either a neutron star if the mass of the original star was between 8 to 15 solar masses (mass of sun: 3 x 10^30 kg)or a black hole if the original star had a mass greater than 15 solar masses.

The death of a stars lays foundations for the birth of the next generation of stars which then gives birth to magnificent species that set out to explore and unlock the cosmos. It is really mesmerizing to think that we were once part of the core of a dying star and that we are actually one with the cosmos…

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