Introduction
Stars play an important role for us. The Sun provides us with heat, light and due to the Sun's gravitational pull only earth is in place. But not only the sun, but other stars also helped us. All the elements we have today are formed inside a star’s core, and after their death we got all those elements.
And in this post we are going to tell you What are star exactly are and how they formed, And classification of stars and death of stars too, in short we are going to tell you everything about Stars. So let’s dive right in.
What are Stars ?
A giant luminous ball of hydrogen and helium is called a star. Nuclear fusion takes place in the star and Hydrogen present inside the core of the star is converted into helium. Due to this process a large amount of light, heat and radiation is given out by the star.
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| Star, Image source : Wonderopolis |
Stars are the most widely observable object in space, and due to the star only other celestial and heavenly objects like planets, other stars, Black holes, nebulae are formed. Even life on earth has come due to our nearest star sun, who provided many things essential for the development of life.
How are stars formed ?
All the stars in the universe have arised from the residues of previous stars. All stars are formed in the huge lumps of dust and gases called Interstellar clouds. Then due to gravitational pull, the interstellar cloud starts to collapse and all the hydrogen and other gases start to get collected in the centre. After many years huge lumps of gases and dust are formed.
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| Interstellar cloud, Image source : Esa hubble |
Due to all this gases and dust, in the center of the star there is extremely high pressure and compression, Which causes the gases in the centre to heat, at this state it is called a prostar. And with years the temperature and compression starts to increase, and form the core of the star.
When the temperature and compression reaches its highest limit. Nuclear fusion starts inside the star causing the hydrogen to get converted into helium. This releases a huge amount of energy and the life cycle of the star begins. In the process of Nuclear fusion heat, radiation and light is released.
Classification of stars ?
There are around 1 × 1024 stars in the observable universe, But each star doesn’t look the same when observed. So, stars are classified into various types based on their spectral and electromagnetic characteristics. Currently astronomers classify the stars based on the Morgan-Keenan system, under which they are classified using letters O,B,A,F,G,K,M. Under their subtypes they are classified using numbers (0-9) like F1, G1. Our sun is a G2V star.
Stellar classification
O type of star
The O type of star is the brightest star and has a luminosity of 14,00,000 times more than the sun. They are Blue in colour and they have temperatures over 25,000 K and have a mass of around 60 solar masses, and radius around 15 times the sun. They have a lifespan of 10 million years. They are very rare and after a supernova they transform into black hole or neutron star.
B type of star
The B type of star has a luminosity of 20,000 times more than the sun.They are Blue in colour and have a temperature between 12,000 to 25,000 K and mass of around 17 solar mass, and radius around 7 times more than the sun. They have a lifespan of 100 million years. They are also rare and after a supernova they transform into neutron stars.
A type of star
The type of star has a luminosity of 80 times more than the sun. They are blue in colour and have a temperature between 8000 - 11000 k and a mass of around 3.2 solar masses, and radius around 2.5 times more than the sun. They have a lifespan of 1 billion years. They are also rare and after a supernova they transform into a neutron star or Pulsar.
F type of star
The F type of star has a luminosity of 6 times more than the sun. They are blue or white and colour and have a temperature between 6500-7500 k and have a mass of around 1.7 solar mass, and radius around 1.3 times more than the sun. They have a lifespan of 5 billion years. They are not that rare and either they go for Supernova or form a planetary Nebula.
G type of star
The G type of star has a luminosity of as much as our sun and They are White or yellow in colour and have a temperature between 5,000-6500 k and have a mass which is almost as much as our sun. They have a lifespan of 10 billion years. They are not rare and common in space and transform into a Red giant at the end of life, Our sun also comes under this category.
K type of star
The K type of star has luminosity which is only 0.4 times of our sun and they are Orange or red in colour and have a temperature between 3,500-5,000 k and have a mass of 0.8 solar mass. They have a lifespan of 50 billion years. They are the second most common star and transform into a red giant.
M type of star
The M type of star has luminosity which is 0.04 times of the sun and they are red in colour and have temperature under 3500 k and have a mass of 0.3 solar mass. They have a lifespan of 100 billion years. They are the most common star and are very faint thus not visible and transform into Red giant.
Hertzsprung Diagram
Moreover the stars are also classified by using the Hertzsprung diagram also called HR diagram. He made a graph based on Luminosity and temperature, and started to put data of various stars and found that a line was running from highest luminosity to lowest temperature.
In this line 90% of the star started to come and this line was then called the main sequence. Most of the stars we observe today come under the main sequence. Further from it stars were divided further into more types.
Main sequence stars
About 80% of the stars in the universe are the Main sequence stars. These stars fuse hydrogen atoms to form helium atoms using the process of nuclear fusion. This process releases a high amount of energy. Which helps start to live. Stars from O type to M type fall under this category. Our sun also falls under this category.
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| Main sequence star, Image source : Wonderopolis |
White dwarf stars
When the main sequence star explodes in a supernova explosion. Then the surface of the star is lost in space and the star is left with a very dense core which is called White dwarf. White dwarfs have the size of earth but the mass of the entire sun. They glow with the help of electron degrency. They have very high temperature but are not that luminous thus comes in the bottom left corner of HR diagram.
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| White dwarf, Image source : Forbes |
Red dwarf stars
Red dwarf star comes at the end of the main sequence. They are not high in temperature and luminosity. Thus they come under the category of K type or M type of star. They are the most common star in the universe and have the least luminosity thus not visible by naked eyes. Our closest star proxima centauri is also a Red dwarf star.
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| Red dwarf star, Image source : The planets |
Yellow dwarf stars
The yellow dwarf stars come in the center of the Main sequence. Our sun is also a yellow dwarf star. These stars are also called G stars or G type main sequence stars. These stars fall under the category G type of star. They have a temperature between 5000 to 6500 k and 10% of star in universe are yellow dwarf star.
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| Yellow dwarf star, Image source : Astronomy trek |
Red giant stars
Red giant stars are the final state of stars like Type G,K,M stars. They are luminous and large in size. When the star’s hydrogen fuel starts to run out. The star to balance the gravitational force starts thermonuclear fusion due to which the star starts to expand causing its radius to get increased.
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| Red giant star, Image source : The planets |
When the entire hydrogen fuel ends. Due to no opposing force to gravity. The entire star collapses into the star core. And forms a White dwarf star. Our sun after 5 billion is going to turn into Red giant star
Blue giants
Blue giants are formed when a large star starts to expand as its hydrogen fuel starts to exhaust. The star to balance the gravitational force and pressure starts to expand and form a Blue giant star. Blue giants are extremely large in size. They have a cold temperature but still are very luminous. After running out of fuel completely it starts to become a red supergiant. They fall under the category of O and B type of star.
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| Blue giants, Image source : Astronomy trek |
Neutron stars
When a star of type O or B explodes into a supernova. Then the surface of the star collapses into the star’s core which causes a huge explosion. But most of the mass is not lost by the object during the explosion. Due to which it is compressed into a size of 20- 23 km in diameter, but has mass of 15 to 25 solar masses and this is called the Neutron star.
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| Pulsar, Image source : BBC |
Neutron stars which rotate with very high speed and release strong electromagnetic radiation from poles are called Pulsar’s.
How does the star end ?
How the star will end completely depends on the mass of the star. The stars having large mass run out of their fuel very quickly due to which the star's gravitational force starts to compress it, and then it explodes causing a supernova.
When a star of low mass starts to run out of fuel it starts to expand to control the gravitational force and pressure from the star, thus forming a red giant or blue giant based on the mass. Stars of both high mass and low mass leave behind something. Like a nebula cluster, black hole, Neutron star, white dwarf etc.
Conclusion
So this was all for today ,and we hope that you would have got some new knowledge today about STARS. The important point of post were -
- All the elements we have today are formed inside a star’s core.
- A giant luminous ball of hydrogen and helium is called a star. Nuclear fusion takes place in the star and Hydrogen present inside the core of the star is converted into helium. Due to this process a large amount of light, heat and radiation is given out by the star.
- All stars are formed in the huge lumps of dust and gases called Interstellar clouds
- Due to gravitational pull, the interstellar cloud starts to collapse and all the hydrogen and other gases start to get collected in the centre.
- In the centre of the star there is extremely high pressure and compression, Which causes the gases in the centre to heat, at this state it is called a prostar.
- Nuclear fusion starts inside the star causing the hydrogen to get converted into helium.
- There are around 1 × 1024 stars in the observable universe.
- Morgan-Keenan system, under which they are classified using letters O,B,A,F,G,K,M
- The O type of star is the brightest star and has a luminosity of 14,00,000 times more than the sun.
- The B type of star have the luminosity of 20,000 times more than sun
- The type of star has a luminosity of 80 times more than the sun.
- The F type of star has a luminosity of 6 times more than the sun.
- The G type of star has a luminosity of as much as our sun
- The K type of star has luminosity which is only 0.4 times of our sun.
- The M type of star has luminosity which is 0.04 times of the sun
- stars are also classified by using the Hertzsprung diagram also called HR diagram
- About 80% of the stars in the universe are the Main sequence stars.
- White dwarfs have the size of earth but the mass of the entire sun.
- Our closest star proxima centauri is also a Red dwarf star.
- 10% of stars in the universe are yellow dwarf stars.
- Red giant stars are the final state of stars like Type G,K,M stars.
- Blue giants are formed when a large star starts to expand as its hydrogen fuel starts to exhaust.
- Neutron stars which rotate with very high speed and release strong electromagnetic radiation from poles are called Pulsar’s
- How the star will end completely depends on the mass of the star.
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