In the night sky, you can make out hundreds of stars twinkling. You know that they appear small because they are so so far away...

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Star Life

Hello Readers!

In the night sky, you can make out hundreds of stars twinkling. You may find that the stars appear the same size. You know that they appear small because they are so so far away. But stars differ greatly in size, colour, and lifespan.

First, we need to know how a star is born. For instance, how the sun is born and how the earth came into existence.

Step 1: For a star formation, a cloud of dust and gas is necessary. For instance, nebulae can be used too. Then the cloud or nebula must be disturbed. A nearby supernova or a Kilonova (Explosion due to the collision of neutron stars) can do the job. Over time, gravity turns the cloud into many fragments.

Step 2: The fragment which has the necessary gas and dust to trigger a star formation is shaped into a disc. This disc (called Protostar) starts rotating. The centres of these protostars turn the fastest and trigger nuclear fusion. Nuclear fusions can make gas and fire erupt from the centres.

Nuclear Fusion: The process where two atoms are smashed together to get energy, neutrons, and subatomic particles called positrons and neutrinos. 

Step 3: The centres get so much mass that they actually explode, blowing the ring of gas and dust away. This explosion is termed a Type 1a supernova. The centre now becomes a stable star.

There are three types of stars according to their size and lifespan- Small stars, Medium stars, and Large stars

Small Stars: The stars with a mass less than half the mass of our sun are called Small stars. They are barely so big enough that they can fuse hydrogen into helium. Small stars have limited hydrogen fuel but burn it so slowly that they can last up to a trillion years. In small stars we have - Red dwarfs, Orange Dwarfs, Brown Dwarfs, and White dwarfs (Small Stars that have used up their entire hydrogen fuel). These stars after exhausting hydrogen fuel shrink and fade until they become white dwarfs. After that, they fade away into cold, dead black dwarfs.

Medium Stars: Stars with mass the same as the sun is Medium stars. They last up to 10 billion years (The sun had existed for 4.5 billion years and had burnt about 50% of its hydrogen fuel). These stars expand as they near their end because they try to fuse helium into a Red giant star and many engulf any nearby planets (In the Sun's case, it will engulf Mercury and Venus and reach out to Earth's orbit). Then the star would disintegrate into a glowing, ghostly cloud of wreckage called a nebula. As mentioned before, this nebula could be recycled for new stars. The remains of the star would be its core called a White dwarf.

Large Stars: Finally we come into the massive collection of stars. These stars have a mass of more than three times the mass of our sun and last for a few billion years (possibly a few million years). These stars are born as big stars, expand as they age, and die in the most violent, destructive way possible. They start as blue giant stars, expand and become red supergiants to red hypergiants. These stars expand to so massive sizes because they can fuse helium into Neon. The Neon is fused into Silicon and it is fused into Carbon and fuse into Oxygen and into finally Iron. At the hypergiants stage, the nuclear fusion in the star tries to fuse itself which causes it to shrink into a single point called singularity at a speed of quarter the speed of light (300,000 km/s) and they explode in a catastrophic explosion called Supernova (Type 2 supernova).

Depending upon the mass of the star, the remnants (the core) are turned into a neutron star (the densest object in the known universe) or a black hole (a region with gravitational pull and the speed of light). Smaller supergiants become neutron stars. But bigger supergiants become Black holes.    

So this was the life cycle of stars.

We now see the ascending order of these stars.

The Hertzprung-Russell diagram (by Google)

This diagram is called The Hertzprung-Russell Diagram. It is a graph plotted by astronomers, Ejnar Hertzprung and Henry Russell. It shows the types of stars depending on their size, magnitude, and temperature. The smaller stars are the stars in the main sequence, The Red dwarfs to the Blue-White Giants. The bigger ones are supergiants and hypergiants, older stars which are a part of the main sequence millions of years ago.

According to this diagram, blue stars are hotter(tending toward a maximum of 12,000 deg. Celsius) and red stars are cooler(tending towards a minimum of 3,000 deg Celsius).

The stars and their instances are-

1) White dwarfs 

2) Red Dwarfs - Proxima Centauri

3) Yellow Dwarfs - Alpha Centauri, Sun, 51 Pegasi

4) Red giants - Aldebaran, Arcturus

5) Blue giants - Spica, Virgo, Alcyone

6) Blue-white giants - Electra

7) Red supergiants - Antares, Betelgeuse

8) Red hypergiants - UY Scuti, Stephenson 2-18

Fact: The densest stars in the known universe are Neutron stars, the remnants of exploded stars. The densest alive stars are Red Dwarfs, stars that have a mass less than half of the Sun's mass. Interestingly, adding more mass to a red dwarf doesn't make it bigger but its insides denser.  

Thank you for Reading!

Aditya VN Kadiyala