Introduction to Astrophysics #1 – Akshay kumar das

Let us know more about stellar evolution, we all will be surely amazed by this extraordinary process of star birth to death. Why do nations invest so much money for research in Astrophysics? Have ever thought, consider NASA, they invest billions on to the Space and Astrophysics, You know the science of stellar evolution and its study has greater significance in knowing the fundamental evolution of this universe, which in turn helps us to know the origin of life, earth and for the matter.. Us and fate of universe.

How amazing, beautiful to eyes to look at the Dark night sky filled with countless stars. Can’t believe our sun is a star. The nearest star.

The facts you learned during school-days will surely be updated now, but the curiosity of stars are still the same for me. I still look into the night sky as a mysterious scene.

Today let’s read about Stellar evolution:

 1. Birth of a star :

Once a protostar condenses to a sufficient density, hydrogen in its core begins to fuse, and it becomes a main sequence star (on the main sequence on a Hertzsprung-Russell diagram)



Image result for Hertzsprung-Russell diagram
Hertzsprung-Russell diagram

2. Main Sequence :

During the majority of a “light” stars life, the center of the star has a high enough temperature and pressure that hydrogen atoms fuse to form helium. This process releases an energy, which further increases the temperature and pressure in the center of the star.

Eventually, this energy will work its way out of to the edges of the star, and will escape as light or other electromagnetic energy.

Image result for main sequence star

3. Evolution :

The star eventually runs out of hydrogen to “burn” in its center, and, if the temperature and pressure are high enough, helium will fuse into carbon, nitrogen and oxygen. CNO Cycle The CNO cycle (for carbon–nitrogen–oxygen) is one of the two known sets of fusion reactions by which stars convert hydrogen to helium, the other being the proton–proton chain reaction (pp-chain reaction).

Unlike the latter, the CNO cycle is a catalytic cycle.

It is dominant in stars that are more than 1.3 times as massive as the Sun.

The CNO Cycle is not the process of fusing helium into carbon, nitrogen and oxygen!!! The CNO cycle describes how hydrogen is fused to helium, using carbon as a sort of katalysator.

Image result for CNO Cycle
CNO Cycle

3. Death of a star:

When the star can no longer support fusion in its core, its internal energy source is depleted, and it will slowly cool to be a white dwarf. One famous example of a white dwarf is Sirius B, companion of Sirius.

Image result for death of a star

It is believed that Sirius B was more massive than Sirius itself. However, Sirius B now has as much mass as the Sun but is the size of Earth. Sirius B is very likely a new white dwarf, because it is one of the hottest known white dwarfs, with a surface temperature of about 26000 K. For comparison, the Sun’s surface temperature is about 5770 K. In some other cases, the star will collapse and create an enormous explosion called supernova. Supernovae are extremely rare, for it only happens with a star at least 10 times bigger than our own Sun.

Image result for sirius binary star
Sirius (Binary star)

A white dwarf is believed to maintain its existence by electron degeneracy pressure. Pauli’s Exclusion Principle, which states that no two electrons can be in the exact same state, provides a degeneracy pressure, which keeps the star from collapsing under its own gravity.

Pauli Exclusion Principle

Image result for Pauli's Exclusion Principle 

white dwarf

Image result for white dwarf

The critical mass for a white dwarf is about 1.4 × Msun. This is mass is known as the Chandrasekhar Limit, which no white dwarf can exceed.

Image result for Chandrasekhar Limit
Chandrasekhar Limit


For Future reading:



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