We’ve all heard that one day the Sun would swell up and consume the Earth. Though it would take billions of years and we wouldn’t be there to see it happen. But would it actually happen? And if so, then why? To understand the how and why, we must learn about Red Giant Stars. Red Giant Stars are more of a phase in the life of the stars, rather than being a type of star. And this is the phase that we refer to when we talk about the Sun swelling up and consuming Earth. This phase in the life of our sun is one that almost every average or small-sized star has to go through. So, let’s take a look.
Life of Star
From its birth to its death, just like us, there are different phases in the life of a star. Why don’t we go through the entire cycle up to the point where the stars turn into Red Giant Stars.
Some stars were born right after the Big Bang and other than them most stars are born in Stellar Nebulae. Stellar Nebulae are giant clouds of dust and gas. In these clouds, gravity amasses the gases and dust into balls. These balls with their gravity now start pulling more and more matter and keep growing in size. Soon they reach the point where the density, gravity and heat of these balls are enough to ignite the fusion reaction of Hydrogen in their core. This turns these spheres into burning balls of gases that we know as stars.
When juxtaposed to humans, this phase is like the incubation and birth of a human baby. And next this baby has to grow and struggle against the world to survive. Stars do the same. For a star to survive it has to constantly burn Hydrogen in its fusion reaction in its core and maintain a very delicate balance between gravity and energy.
Balance of Gravity and Energy
We know that the stars constantly burn Hydrogen in the fusion reaction. This generates Helium and energy.
The energy generated pushes outwards against all the layers of the star. The star’s gravity pushes inwards. The balance between these two forces is what’s important for the survival of the star. The imbalance in this arrangement is what marks the beginning of the death of a star. From this point on the average and small-sized stars follow the path that leads to them becoming White Dwarf Stars, the senile phase of the stars’ lives.
However, before the stars turn into White Dwarf Stars, they go through the phase of Red Giant Stars.
Red Giant Stars
Within the core of the star the process of fusion reaction of Hydrogen results in the generation and accumulation of Helium.
Moreover, as we have noted earlier, the balance between the outward force of energy and the inwards force of gravity is essential for the life of a star. So, when the star runs out of fuel, that is Hydrogen, for the fusion reaction, it disrupts the balance between the two forces.
Now, the core of the star, which has run out of Hydrogen and is made up of mostly Helium, is crushed under the gravitational forces. This creates enough heat to start the fusion reaction in the shell of the Hydrogen surrounding the core. Now, this shell once again pushes outwards against all the other layers of the star. Since the Hydrogen in this shell is more than there was in the core, the outwards forces are greater and the star swells up larger than before, turning into a Red Giant Star.
This process does not happen just once. As the star runs out of Hydrogen in this shell, the gravitation forces overpower once again and the star shrinks in size until another layer of Hydrogen is heated enough to start fusion.
The stars shrink and swell up a few times before running out of Hydrogen completely and starting the fusion of Helium into Carbon and Oxygen. At this point the star swells up one last time, turning into a Red Giant Star. And soon, it starts shedding away its many outer layers into a beautiful Planetary Nebula.
What phase of human life would you juxtapose with the Red Giant Star?