Even stars die, but they die out in fashion. Some go boom (supernova explosion), some swell up like balloons and some end up as black holes. We have already written about supernova and black holes.

Let us to learn 20 interesting Red Giant star facts. Red Giants refer to the ones that swell up like balloons. Let us find out what causes such swelling up and what type of stars end up as Red Giants.

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1. Stars that are about the size of our very own Sun end up as Red Giants at the end of their lives. As far as the fate of our Sun is concerned, it is not going to die anytime sooner than 5 billion years from now. So, we are pretty much safe unless of course a freak asteroid is sent hurling towards Earth for a catastrophic extinction-level impact before Sun’s life ends.

2. Stars that are 1/3rd to 8 times the size of sun end up as Red Giant Stars. Now stars are usually made up of a gas called hydrogen. At the core of a star, the every two atoms of hydrogen fuse together to form one atom of helium – a heavier gas than hydrogen. This fusion is called nuclear fusion reaction.

3. The problem with stars is simple, they fuse hydrogen into helium at their core (very center), and hence, helium has nowhere to go. After billions of years of fusion reaction, stars accumulate huge quantities of helium at their cores and gradually, hydrogen that made up a star is slowly burned out (we mean fused into helium).

4. Hydrogen is the fuel that keeps stars alive. When the hydrogen is gone, the stars have no hydrogen molecules to fuse. This is where the stars come to the end of their lives.

5. During this whole lifespan, i.e. when hydrogen is fused into helium, an external pressure is created because of the fusion reaction. It is this external pressure that keeps stars from collapsing because of the immense gravitation at the core of the stars.

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6. With no external pressure left, the stars now succumb to the gravitational pull of their cores. With strong gravity into play, the stars now star contracting in on their own core. So, the stars become tighter and smaller.

7. With the onset of the compression, the stars heat up gradually because more and more mass is getting packed in smaller and smaller space. The gradual buildup of temperature eventually reaches a point where the helium present in the stars can now start fusing together into carbon atoms and oxygen atoms.

8. This helium fusion can start with a sudden and explosive flash or it can start gradually and slowly. Exactly how the helium fusion starts is dependent on the mass of the star.

9. Again, fusion reaction releases energy. This massive amount of energy produced because of helium fusing into carbon is trapped inside and tries to go out. This leads to enormous pressure buildup which in turn starts pushing outwards. This leads the stars to expand.

10. At this expansion phase, the stars begin to swell up. They expand and expand and expand until they grow massive with their diameter ranging between 100 million kilometers to 1 billion kilometers. In other words, they grown in size by about 100 times to 1,000 times their original size.

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11. After this massive swelling up, the energy that is created because of helium fusing in carbon is now spread over a bigger surface area. Since the pressure is no longer concentrated on a smaller surface area, the surface temperature of the giants so formed have lower temperature.

12. The surface temperature of the giants formed is way cooler that the surface temperature they had when they were fusing hydrogen into helium. In fact, now the temperature drops to about half the original temperature.

13. Red Giant stars have a surface temperature ranging between 2,200°C (or 4,000°F) and 3,200°C (or 5,800°F).

14. At this temperature range, the stars appear yellow-orange to bright red in color, and hence, the name Red Giant stars.

15. Some Red Giants still managed to have some hydrogen left in the outer shell that continue to fuse into helium while the helium in the core continues to fuse into carbon.

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16. The Red Giant stars continue to fuse helium into carbon for around another 1 billion years or so. During this process, the helium at their cores continue to fuse into carbon. When there is no more helium left for fusion, the stars start shrinking again. This is when the helium from the outer shell move towards the core and is ignited.

17. When the helium of the outer shell reaches the core and ignites, the outer layers eventually blown off as gas clouds. These gas clouds are known as planetary nebulae. However, even though the outer layers blow off as planetary nebulae, they core continues the collapse on itself, eventually forming white dwarf stars. They just hang around there in the vastness.

18. However in case of very big stars, the final collapse can eventually lead to supernova where the core meets a violent and fiery exploding death. However, stars of the size of sun end up as white dwarfs. These are just medium sized stars that no longer burn and the core that is still glowing is left out there for cooling in the vastness of the universe for eternity.

19. Gamma Crucis is the nearest Red Giant to us. It is at a distance of 88 light years from us. This star is actually red in color. Another one which is far closer is just 36 light years from us. It is known as Arcturus. Arcturus is an orange giant.

20. What will happen to our sun? The inevitable! It will turn into a Red Giant star. When it balloons up, it will comfortably consume both Mercury and Venus. Some scientists say that at that stage Sun may even eat up Earth. Other say that the sun will not engulf our home orb, but will get dangerously close. Whatever the case be, life on Earth will no longer exist.

Interesting Fact:

When a star balloons up to become a Red Giant star, its habitable zone also changes. This means that the area where liquid water can exist eventually changes. Since Red Giants have a lifespan of a billion year or so, life can actually flourish for that time frame.

However, when our Sun eventually starts collapsing again, the new habitable zone will once again become barren as the life-giving force – the light of sun will no longer reach the place, turning it back into an icy grave of all life forms.

That concludes our list of red giant star facts. If you want to share your thoughts, comments are open!

Sources: 1, 2, 3, 4

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