Life of Stars – Birth To Death

(Last Updated On: August 19, 2019)

Life of Stars – Birth

We always live our daily life without understanding the mechanics of our world. If we give close thought to mechanics of it, life is possible because of our sun. And if we look in the clear sky at night we see a sky full of ghosts.

Stars - life of stars
Sky – Full With Stars

Our whole universe is filled of these giants and we call them as stars. And our sun is one of them. Stars give us life by burning themselves. But is there a limit to their burning? Do they have a life? How they are formed? Do they have a death? What do we know about them? And where do they go? What happens with them? But due to recent breakthroughs in physics, throughout the last century made the picture clear and give the answers to those questions.

If we see it all started with the Big Bang as it is the best explanation we have. Many people must have heard of it to. But what is the Big Bang? It is like our entire universe is condensed in a single point less than an atom and it contained not only all energy but also every atom that exists. Even time and space didn’t exist before this massive event. Scientists call this as The Big Bang Singularity. This huge event happened around 13.7 billion years ago. This tiny particle exploded and threw a large amount of matter and energy in a matter of microseconds and universe started to build and went on expanding till the moment what we see now and it is still expanding.

The Big Bang Theory - life of stars
The Big Bang Theory – Expansion Of The Universe (Credit – How Stuff Works)

And here gravity played the main role, due to gravity some atoms came close and made clouds. Clouds went on becoming denser and denser and hence first stars were formed from the clouds of hydrogen and helium. And the death of these first stars built our universe which we see now.

We’ll see the death of stars further. From the nebula or clouds of hydrogen and helium stars born. Our sun is also born in this way. The gravitational waves spread across universe due to supernovas (i.e. death of star by the explosion) causes nearby nebulas to accumulate the matter to the center, the matter starts revolving around this small globe, this is called as an accretion disc.

accretion disk - life of stars
Accretion Disk

When the fusion of hydrogen starts and optimum pressure is generated this pressure keeps the balance with its own gravity and fusion reaction keeps taking place and this is how a star is born.

The Eagle Nebula
The Eagle Nebula (Nebula – Where Stars Born)

Life of Stars – Journey

Now we have seen the birth of stars. Our sun was born around 5 billion years ago as a protostar and so as the other stars and some of them are older than our sun and some of them are younger. But the question rises what keeps them burning so many years? How do they last long in some billion years? And how many years they will burn this way? How do they measure the age of stars? But thanks to the genius scientist because of whom we can not only calculate their ages but also what will happen to them when their fuel burns up completely.

Stars start their life as a protostar. At the start, they are super hot. Proto stars transform into the blue supergiants or into sun-like stars or into the dwarf stars. This transformation of stars tells us how the star will die. Supergiants turn either into supernovas or into red giants or in some of the cases into black holes. Sun-like stars convert into red giants and further into the planetary nebula and white dwarfs. And dwarf stars transform into red dwarfs and brown dwarfs.

Stars are mainly massive spheres of hydrogen and helium. Four hydrogen atoms come together and form a single atom of helium but it is in general. Energy is given out in this process. When 2 hydrogen collides with each other and creates deuterium. While this reaction 1.44 MeV energy is given out. Previously formed deuterium collides with another hydrogen atom and forms Helium-3 (3He), which is a light isotope of Helium. 5.49 MeV energy is given out in this process. From this, there are 2 ways in which He-3 is converted into the helium atom. Either by fusing 2 3He atoms with each other or by fusing 3He and pre-existing Helium (4He) atom, which produces 7Be which again undergoes in fission reaction and forms 2 helium (4He) atom. And throughout all this reaction a tremendous amount of energy is given out. This reaction is called as P-P cycle.

But this is not the only reaction that happens into the stars, which produces energy. There is another reaction known as the CNO cycle. In this process reaction takes place from carbon atoms to nitrogen formation to oxygen formation, while this process is taking place at the end of the cycle helium is given out with a large amount of energy. But the P-P cycle takes place in those stars which are same or lesser than our sun in size. While the CNO cycle takes place in the stars which are more than 1.3 times the size of our sun. In those bigger stars, these reactions are more in the core that’s why some of the elements are formed there up to iron.

The classification of stars is made on the basis of their luminosity. The colors of the stars represent their temperatures. Blue stars are very hot, their surface temp. ranges between 50000 K to 28000 K. Whereas red stars are comparatively cool, their surface temp. ranges between 3500 K to 2000 K.

Life of Stars – Death

Stars also have aged. They born, they live their life and they face death also. And their death depends upon their mass. After their death stars leave behind the marks of their existence in the forms of dwarfs or neutron stars or pulsars or black holes.

1. Brown Dwarfs: Very small stars mainly brown or red dwarf stars when reaching their limits they collapse and becomes brown dwarfs.

2. White Dwarfs: When a star nearly same size of our sun dies, the whole mass of sun contracts under its own gravity and collapse completely that a small spoon fully filled from this dwarf weighs more than a large city. Our sun will be a white dwarf after 5 billion years so we don’t have to worry about it.

3. Neutron stars and pulsars: When a star weighing more than 1.44 times than our sun collapse under its own gravity it becomes a neutron star. Its matter is denser than the matter from the white dwarf. The 1.44 limit is known as C-limit and named after the Indian Scientist Chandrashekhar Subrahmanyam. Pulsars are also regular neutron stars but they throw out the matter from their poles. And their spinning is so fast hence it seems like a beam of light or like a pulse and therefore called a pulsar. Pulsar from crab nebula spins 33 revolutions per second. Mostly neutron stars and pulsars are formed by the supernovas i.e. explosion of the star. It is so humongous that it shines like hundreds of stars are present there. It appears brighter than the stars to the eyes. This supernova after becomes nebulas from where stars are born.

The Crab Nebula
The Crab Nebula (Supernova)

4. Black Holes: Black holes are formed by mostly 2 ways. When a blue supergiant in his old age transforms into red supergiant, then the giant collapse under its own gravity and the black holes are formed. Or when a blue supergiant in his old age transforms into red supergiant, then the giant can’t stabilize the balance between internal pressure and its own gravity and a huge supernova is formed and the core of it becomes a Black hole. But to happen all this mass of the star must be more than 3 times than our sun.

Conclusion

Our universe is filled with the trillions of stars but the distance between two stars is so large that we can’t even imagine. They are very very far from us. We just see their old forms only as the light left from them requires hundreds even thousands of years to reach to us. Some of them are still living but some of them are dead decades ago. We are just seeing their souls only. The sky is full of ghosts.

Read Also – 1. Life of Small Stars

2. Life of Large Stars

References:

1. A Brief History of Time By Stephen Hawking

2. The Universe in Nutshell By Stephen Hawking

3. The Structure And Composition of Cosmos (University of Copenhagen) By Jorgen Balslev

Bhalchandra Ravindra Yalamali

Bhalchandra Ravindra Yalamali

He is an astrophysics lover. He loves to explore the field of astrophysics.

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