Life of a Star

Life of a Star

Looking outside, at the vast expanse of space, stars illuminate the dark and mysterious blanket over us all. Perhaps the most fascinating astronomical giants, they are definitely intriguing from the inside but contain a wealth of secrets, on the inside. One such secret which I am about to explore though this article is the birth and death of a star.

So, how are stars born? Stars originate from huge, cold clouds of dust and gas( largely hydrogen) in space. Over time, gravity starts to pull this matter together and a highly dense area is formed, known as the core of the star. As gravity slowly collects more and more matter at this concentrated area, temperature and pressure begin to rise.

When temperatures in the core exceed 10 – 15 million kelvin, the hydrogen atoms in the core begin to fuse together, which results in the formation of Helium. This process releases enormous amounts of heat and light. This is called the birth of a star, as it starts emitting light, much like the Sun. The star is kept from collapsing on itself due to the force of its own gravity by the release of heat and light.

Depending on the mass of the star, the hydrogen in its core can keep fusing for millions or billions of years. When the hydrogen at the core is depleted, the core shrinks and heats. But, the gravitational force is weakened (as it loses mass) so the outer layers of the star start to expand. 

The star now can grow from 100-1000 times the diameter of the original star and is called a  Red Giant. At about 100 million kelvin inside the core, Helium starts to fuse into Carbon and Oxygen. After the core is left only with Carbon and Oxygen, the life of the star depends on its mass.

If its mass is enough to create temperatures of 600 million kelvin in the core, carbon and oxygen can fuse into heavier elements, which form rings around the shrinking core. The star can keep fusing elements until it reaches Iron (26th on the Periodic Table).  The fusion of Iron is an endothermic process, due to which there is no force to counteract gravity. The star collapses in on itself and the electrons and protons released combine to form Neutrons.

Soon the core reaches an extreme point where it recoils and explodes outwards. This is called a Supernova. For stars about 9-20 times the mass of our sun, the remnant of the explosion is a neutron star, which is incredibly dense. This is called a black hole and even light can’t escape it.

Stars about the mass of the sun will never be able to fuse Carbon and Oxygen, due to which the star becomes unstable and sheds all outer layers, creating a Planetary Nebula. Soon it collapses in on itself, forming an object about the size of Earth, with mass 2-3 times the sun. This is a White Dwarf, which radiates all its heat and light over trillions of years, cooling to form a black dwarf (which scientists don’t believe exist yet). Stephen Hawking once said, “ Remember to look up at the stars, and not down at your feet”. These are just some of the secrets that the vast cosmos holds. There are many more surprises, waiting to be discovered, and change the course of physics.

– Saarthak Khosla

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