A red supergiant is the final phase of the life of a giant star. But how do they work? What would be happening at the very core?

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 Red Supergiants

Betelgeuse - A red supergiant (by Google)

We have seen about the types of phases of giant stars in Star Life. Giant stars are born with blue colour, evolve bigger as they age and turn redder. So the biggest stage is the final phase of their very lives, where they are thousands of times more massive than they used to be. They are in pure red and orange colour. 

Also, blue indicates the hottest stars and red indicates the coldest stars, not the reverse. Also, coldest means that they have relatively less temperature than other stars.

Blue: 25,000 C (45,032 F)

White: 10,000 C (18,032 F)

Yellow: 6,000 C (10,832 F)

Orange: 4,000 C (7,232 F)

Red: 3,000 C (5,432 F)

Comparison with our Solar System

A typical red supergiant, such as Betelgeuse (the image shown above) is about 700 solar masses. Fitting it at the sun's place, would reach out past Mercury, Venus, Earth, Mars, and The asteroid belt and stop at Jupiter's orbit. We might think, it is not as big as it is credited for since it hasn't reached out to half of the Outer Solar System, but in reality, all planets are spaced apart beyond what we actually think are. Saturn is 10 AU (AU or Astronomical Unit defines the distance between Sun and Earth or 150,000,000 km) but Neptune is 30 AU. 

Working of a Red Supergiant

We are going to use the term - Nuclear Fusion since it is used to produce energy by all-stars.

Nuclear Fusion: It is a way of making energy whereupon you smash two atoms together to release a lot of energy and also an isotope of the material.

Isotope: Atoms have a different number of protons and electrons (electrically neutral) so they are divided into different atoms according to their atomic number (a number that denotes the number of protons or electrons, since they are in equal number). But Neutrons add weight to the atom. Take Hydrogen, for instance, it has 1 proton and electron but it may have 1 neutron or 2 neutrons or more. So isotopes are atoms of the same element that have a different number of neutrons or are unequal in weight.

Our sun uses its hydrogen in nuclear fusion, it is the hydrogen it has obtained due to the nebula in its forming period. It fuses hydrogen to release tons and tons of energy that we receive as heat and light. It also forms helium. But at around 5,000,000,000 years into the future, it would have used up all its fuel. Whatever is left is only helium. Then, the sun has no other option but to continue the fusion process, however this time with helium. Then disaster strikes the earth. The helium fusion brings more energy than today that will cause the star to expand as its layers start to become dense, It will reach Earth's orbit, where it is in the final phase of life and stabilize. Then it could be potentially renamed from The Sun to The Red Giant Sun. Later, the star would collapse and die in an explosion known as Nova. The earth would likely be destroyed as a whole in the nova.

Facts-

1. The Sun would increase its luminosity by 10% in 1,000,000,000 years. So, 1,000,000,000 years back, we got 10% less light than today. Similarly, we would get 10% more light in 1,000,000,000 years.
2. After becoming a red giant star, The Red Giant Sun would stabilize for another 5,000,000,000 years before it collapses. 
3. Currently, the average temperature on Earth is 16 deg. C, but in 1,000,000,000 years it would rise to 47 deg. C because of a change of luminosity from the sun.
4. If the sun disappeared, we would see it disappear after 8 minutes and 17 seconds.
5. It takes roughly 8 minutes and 17 seconds for the light from the sun to reach Earth. But it takes 100,000 years for the energy to reach from core to surface.

Stars as massive as Betelgeuse, and Antares A have so much fuel, they can surpass the red giant size and grow bigger. They can fuse Hydrogen (H2) to Helium (He) Carbon (C) to Neon (Ne) Oxygen (O) to Silicon (Si) to Iron. 

Some stars can age up to Red Supergiants, the commonest end phase of stars and also the massive version of Red Giant. Like Betelgeuse, Antares A. They can also swell up to Red Hypergiants. Like VY Canis Majoris and UY Scuti.

These stars fuse hydrogen for creating power that is equal to the force of gravity constantly trying to implode the stars. The extra power is emitted by the star as heat, light and solar wind.

But large stars, when they fuse their own iron core, produce less energy to counteract the force of gravity. It implodes in a single point that forms a black hole, but NOT yet. It explodes as an explosion known as Supernova. Right after it forms the black hole.

Supernovae

There are 2 types of supernovae, The Type 1 Supernova and the Type 2 Supernova. The Type 1 Supernova occurs when a white dwarf receives the mass of a star as an interacting binary system. Type 2 Supernova occurs when a massive star dies. But there is also a hypothetical Type 3 Supernova or Hypernova which is 10 times more massive than the original supernova.

Thank you for reading.

Aditya VN Kadiyala