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The Story of a Star


Not all the stars are seen at night. The burning sun we see at day is also a star. And in this article I will tell you about the life cycle of a star. Not the ones in Hollywood but the stars out there in the sky.

A star is a celestial body made with mostly hydrogen and helium. They are massive and shines.

How is a Star Born?

There are masses in the universe called molecular clouds. They consist of mostly hydrogen and helium. The birth of the star takes place in these clouds. Sometimes the gravity within the cloud loses its stability and causes the dense matter in the cloud to fall under their own weight. These masses of gas are called a protostar, the earliest phase of a star. These are very difficult to detect as the dust in the nebula obscures them.

What is the Life cycle of the Star?

The protostar gets smaller as it begins to spin faster just like an ice skater spins faster when she pulls her arms in. As the protostar gets smaller the pressure inside increases which causes the inner temperature to rise. This phase is called a “T Tauri star”.

A star passes millions years in this state. Finally when the core temperature is risen up to 15 million Celsius ( about 27 million degrees Fahrenheit ) nuclear fusion begins. Nuclear fusion in a star is simply converting hydrogen into helium. This process releases so much energy which keeps the star hot and shining. It is the next phase of the star called as “Main sequence“. A star spends about 90% of its life time in this phase. They are called dwarf stars.

What does Happen to a Star at the End?

After billions of years later the star reaches the last phase after converting hydrogen into helium. That helium sinks to the star’s core which raise the core temperature of the star. By this time the hydrogen in the core is almost finished therefore it starts to fuse the hydrogen in the outer layers. The gasses in the outer layers begins to expand making the star a ” red giant”.

When the hydrogen is converted into helium the mass of the core increases. When the core temperature is sufficiently increased the star begins helium fusion. The helium fusion begins explosively which is called a “helium flash“. Then the star begins to decrease in size and becomes a “white dwarf”. The white dwarfs stay cool for billions of years. Over a very long period of time the white dwarfs fade into a black dwarf.

But not all stars end up as a black dwarf. Massive stars fusion continues until the iron core becomes so big that eventually it cannot hold its own mass. Then the core collapses and the shock wave caused due to the collapse causes the rest of the star to explode in a supernova. A supernova can be so bright that it may briefly outshine the galaxy that the star reside. After the supernovae the core compresses into a neutron star or if the remnant is massive enough a black hole.

In the following picture the bright spot at the bottom left side is a type Ia supernova in its host galaxy

Hubble Space Telescope image of supernova 1994D in galaxy NGC 4526.

The fate of our sun?

Our sun is a typical star that would end up as a black dwarf.

NASA/SDO (AIA), Public domain, via Wikimedia Commons

Thank you for reading. I hope you have enjoyed the post.

I will be posting a new detailed article about our sun on next Monday.

Thank you ❤ 🙂

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