Different Types of Stars in the Universe | History, Formation and Classification

Different types of stars
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Ancients believed that liberated souls after death went on to become stars in the sky, always looking upon and guiding us, when the Sun was not around. With the coming of age of discoveries and telescopes, we get to realize that stars are not small twinkling lights but rather spherical balls of fire just like the sun.

Our sun is just another star among billions of them around us. Newtonian mechanics and electromagnetism led to the explanation of the composition and internal structure of stars. There are many varieties of stars as we search for them through our advanced telescopes. Some are blue in color, some are yellow like the sun and some are red giants like Betelgeuse in the Orion constellation. Just try to focus on the corner of Orion’s left hand and you will observe an orange star.


Different Types of Stars

So how many different types of stars are there in the universe? Let’s see in this article. Stars can be classified into many categories on the basis of mass, color, temperature, and their evolutionary phases.

Let us talk about stars in various phases of their life starting with on the basis of stellar evolution:

Proto Star

Proto Star is the initial phase star that is formed due to the collapse of nebular gas under its gravitational force. In the initial phase of the star, it has not reached enough temperature to start nuclear fusion, but due to friction produced by the gravitational collapse of the star, heat is generated that makes the star produce light. This phase lasts till 100,000 years or more and subsequently converts into a main-sequence star.

Main Sequence Star

This is a usual star we see around us such as our own sun. The star has reached enough temperature to start its nuclear fusion process. Two hydrogen atoms combine to form a helium atom and in this process produce a lot of heat.

This heat is used in two ways; one is to balance the inward gravitational attraction by providing outward thermal pressure. On the other hand, the left out heat is produced as a source of light and radiation. This state is called a Hydrostatic Equilibrium in which a star is able to retain its spherical shape.

Red Giant Stars

Main sequence stars keep on burning hydrogen and heavier helium atoms get deposited in the core. After consuming all hydrogen, if there is enough heat inside the hearth of the star, then it can fuse helium atoms to form bigger elements, but small stars like the sun cannot produce that much heat.

So when there is little hydrogen left on the outer area of the sun-like stars, it begins to expand or we can use a better term, inflate. This principle is called the Mirror Principle in which, to compensate for a collapsing star, the outer surface gets expanded. This outer core, mostly red or orange in color with an average temperature of 5000 K, inflates to a much bigger volume and that is why it is called a Red Giant Stars.

When after 5 billion years our sun will become a Red giant, it can easily consume the earth that is 150 million kilometers afar.

White Dwarf

After the red giant phase, the heavier core is left and keeps collapsing under its own gravitational pressure. But this compression is causing the particles in the star to come closer. As you may have learned about the Pauli Exclusion Principle from our previous articles, you know that two same quantum particles cannot attain the same state, so they repel each other and this produces a negative pressure called the Electron Degeneracy Pressure.


Pauli Exclusion Principle


This outward pressure balances the inward acting gravitational force and the white dwarf achieves a stable shape. The density of white dwarf is very high. A white dwarf with the size of the earth may contain a mass greater than that of the sun.

Neutron Star

If the mass of the white dwarf is very much high, then the gravitational force wins the tug of war with electron pressure. Indian physicist Subrahmanyan Chandrasekhar had proposed the required mass for an object to remain a white dwarf.

This mass limit is called the Chandrasekhar limit and it is equal to 1.4 times the solar mass. So any object greater than this limit, will collapse further and lead to a stage of a neutron star. A neutron star is the collapsed state of a massive star.

Ordinary matter is made up of

  • Protons
  • Electrons
  • Neutrons

Neutron on decay produces protons, electrons, and antineutrino. This massive compression causes the protons and electrons to fuse and form neutrons. Thus the whole star is composed only of neutrons, hence the name.

When these neutron stars rotate, they leak the magnetic flux from the two poles and this magnificent phenomenon in space is called pulsars as they emit the flux periodically in the form of pulses.

Red dwarfs

Red dwarfs are similar to main sequence stars but have very low mass. They are cooler in temperature and have a very low luminosity. Since its temperature is not high enough, the nuclear fusion process happens very slowly and these types of star take a long time to fuse all the present matter.

Remember this, the bigger the star, the faster it will consume the atoms, and sooner it will die. Red dwarfs usually live for 10 trillion years, that’s a large number. For perspective, the age of the universe is only 14 billion years.

Yellow Dwarf

They are G class stars and their masses are equal to or less than the mass of the sun. The average temperature of the yellow dwarf star is 6000 K. They are yellow in color but overall luminosity appears white.


Also Read: Black Hole and Laws of Thermodynamics 


Blue Giants

They are O-type stars and are usually found in spiral galaxies. The average radius of blue giants is 5-10 times the solar radius and masses are 10-50 times the mass of the sun. They are the most luminous stars in the universe and their luminosity is 100,000 times greater than that of the sun.

As they are such massive structures, they tend to burn fuel much faster than main-sequence stars and thus have low lifetimes. Based upon the physical properties, stars can further be classified into 7 categories named as O, B, A, F, G, K, M. O, B, and A-class stars are massive in shape and temperature is in the range of 10,000-40,000 K and they are highly luminous.


Star Categories
Star Categories


F and G class stars are medium-ranged stars and most of the main sequence stars lie in this range. Our sun is a G-class star. K and M are dwarf stars having mass, temperature, and luminosity lower than that of the sun.

What are your thoughts on the different types of stars in our universe? Let us know in the comments. If you found this post interesting, please leave share it with your friends.

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