Nia M Wardani | A Logbook of Life Discoveries

Will The Sun Die Eventually?

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A human life span is too short to witness the dead of the Sun. To answer this question, scientist will have to observe other stars in the Universe at various points of their life time, and making predictions using theoretical models. The results of all those observations are summarized into a theory about stellar evolution. Stellar evolution is life cycle of stars, starting from its birth, to its death. The life cycle is different depends on the mass of the star. The less massive a star, the longer is its lifetime. The diagram below is a summary of how stars evolve. Let's learn the diagram and see what will happen to the Sun.
Stellar Evolution Diagram
The following descriptions are numbered according to the diagram in the previous post.
1. Star-forming Nebula
It's all start from here. The nebula is formed from molecular dust in space that go closer to each other due to gravitational force. The example is Eagle Nebula or Pillars of Creation.
Eagle Nebula
2. Protostar
Nebula collapse and form fragments, the gravitational potential energy is converted into heat, and the nebula forms a rotating hot gas sphere called protostar. The example is V1647 Orionis.
V1647 Orionis
3. Mid-size star
The protostar continue collecting dust and gas, and it goes very hot so that fusion reaction can happen. The hydrogens are converted into helium, and the size is stable. Yes! The Sun is one of it. In this phase we say that the star is in the Main Sequence. Most stars in this universe is in this phase.
4. Red giant 
In this phase the star starts to burn helium. Some have helium shell.Some have hydrogen shell outside and helium shell inside. The size is huge. That's why we call it 'giant'. The example is Arcturus.
Arcturus (left) and its size comparison with Sun (right). Adapted from Wikipedia
5. Planetary Nebula
When the pressure inside the red giant is too big, the star will release its outer shell, leaving only its core. The shell explodes giving you the wave. Ever drop something into still water and a circular wave spread? Yeah, just like that! The example is Dumbbell Nebula. The dust expelled will form star-forming nebula. After that it forms protostars..and the cycle goes round and round like that.
Messier 27 - Dumbbell Nebula
Dumbbell Nebula by Paul M. Hutchinson
6. White Dwarf
White dwarf is actually what is left from the red giant after explosion. It is the core. The size is very small. The example is Sirius B. (And the last name is Black. Just kidding.)
Sirius A and Sirius B taken from Hubble Space Telescope. The white dwarf Sirius B is the small blue dot at the lower left
7. Black Dwarf
Black dwarf is a white dwarf that has cooled down and emits no light but still maintaining its mass. It is theoretical end of mid-sized stars such as sun. No observation is found because black dwarf will exist after very long time, longer than the age of today's universe.
Those are the cycle for mid-sized stars. For stars with lower mass, the following will happen.
8. Red Dwarf
This star has very low mass. It stays in the main sequence for very very long time.
Proxima Centauri
9. Blue Dwarf
For stars with bigger mass, the cycle would be a bit different.
10. Protostar (bigger one)
Protostars with bigger mass will form massive stars.
11. Massive Star
These are main sequence star which are much more massive than the Sun. For example: Spica.
Spica (α Vir)
12. Red Supergiant
The lifetime of massive stars in the main sequence is short. They will immediately becomes red supergiant.
13. Supernova
If the star is massive enough, the star will expel its shells, in a phenomenon we call supernova. The luminosity of supernova is very bright. It releases huge amount of mass. It left an bright nebula we call supernova remnant. For example is Crab Nebula.
Crab Nebula Supernova Remnant
14. Black Hole
The supernova is leaving a very massive core of the supergiant. The core is very massive that the gravitational field is very strong. Everything is attracted to this core, even light. This is what we call black hole. A hole nothing can escape.
Cygnus X-1
15. Neutron Star
If the core is insufficiently massive to form a black hole, it will be left as a neutron star. The example is LGMX-1 pulsar.

As we understand from the cycle, the Sun is predicted to 'die' and becomes black dwarf. Even before that, when the Sun is leaving the main sequence and becoming red giant, the size of the Sun is so big that the Earth will be 'eaten' by the Sun. The scientists predict, there is still around .....years before it happens. However as science develops, the theoretical prediction may change. Again, we would never know when.


Note: Want to make a poster or wall magazine about stellar evolution? Here is a sample layout.
Nia M Wardani
Hi! Call me Nia. I discover interesting things in life and I love to share them with all people around the world.

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