Introduction
Get ready for an wild and amazing ride through the universe, because we're about to dive in the mysterious world of Black holes. Imagine a place where laws of physics no longer apply and, the fastest thing in universe can also not escape is the Black hole, and in this post we will dive deep into the world of black holes, So lets dive right in.
Table of content -
- Introduction
- What is Black holes ?
- How is a black hole formed ?
- What are Parts of black hole ?
- Classification of black holes ?
- What is inside of a black hole ?
- Can black holes emit light?
- What black hole emit ?
- Which black hole is at the centre of the Milky way ?
- Which is the biggest black hole?
- How black holes die ?
- Conclusion
What is Black holes ?
Black holes is a cosmic body which has an extremely intense gravitational force which does not allow even electromagnetic radiation like light to escape from it. Black holes are invisible and the densest object in the universe. Black holes are formed when a large amount of matter is squeezed into a tiny space.
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| Black hole, Image source : News scientist |
A black hole in simple words is a region in space with intense gravitational pull that nothing can escape it, Black hole could be considered as a giant ferocious beast who eats anything which comes close to it, and is 10 to 10 million times bigger than sun.
A black hole is a space where laws of physics twist and tingle, and the reality is no longer normal, The time around a black hole slows down and we move slower in time due to time dilation as predicted by the famous Special theory of relativity.
The closest black hole to earth in January 2023, is Gaia BH1, it is having a distance of 1600 light years from earth. Many of you may have a question: Why black holes invisible ?, Black holes are invisible as they absorb all the light passing near them and do not even emit light, Which causes it to be invisible.
How is a black hole formed ?
When a large star has a mass of around 3 times the sun explodes into a supernova. The star starts to collapse under its own gravity, which causes the star to collapse into its own core. As the star collapses, the density of the core starts to increase. And then it crosses the limit ( 2 × 1019 kg per cubic metre) after which is gets transformed into a Black hole
Black holes are also formed when two or more neutron stars(second densest object in the universe) collide with each other as these two dense stars collide then a Black hole is formed.
Many of you may have a question : What are black holes made up of ?,
The answer is that black holes are also made up of normal matter, but the difference is that matter is very compressly packed, that even the atoms are crushed due to gravity. They have constituents like the star from which they were formed.
What are Parts of black hole ?
Black hole is divided into mainly 4 parts -
- Event horizon
- Singularity
- Accretion disc
- Photon sphere
Event horizon
Event horizon is like the no escape point of black hole. The black part of the black hole is the event horizon. It appears to be black, because once light enters inside it, it can’t get out of it and as no light is coming out it appears to be black.
Event horizon could be considered as boundary of black hole because anything which crosses event horizon cannot return back. Event horizon has escape velocity of speed of light and no matter which has mass can travel at speed of light, and beyond event horizon escape velocity is more than speed of light thus nothing even light can escape from it
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| Parts of black hole |
Singularity
Singularity is a small point in space, which is located at the centre of black hole. The singularity has infinite mass, infinite density and space and time is completely distorted. In singularity according to some astrologists time does not flow and time does not exist at singularity. And according to the BIG BANG theory our universe has also started from singularity.
Accretion disc
Accretion disc is the outermost part black hole. Accretion disc is composed of gases and dust left by the star. In the accretion disc, due to gravity of black hole the matter starts to rotate around the black hole at a very high speed and gets too hot and releases electromagnetic radiation. The matter then falls into the black hole.
As the matter gets closer to black hole the gravity starts to increase rapidly, so much that if you are falling in black hole your feet will feel more pull than your head. And your legs will start to stretch and you will now be a kilometer long and have the width of a hair strand. This process of stretching is called Spaghettification.
Photon sphere
In the accretion disc matter close to black hole, due to strong gravity and high temperature starts to turn in plasma state and releases photons. The photons normally go in a straight line but due to the strong gravity of black hole they rotate around the black hole. Thus forming a bright ring around black hole, this is called Photon sphere.
Classification of black holes ?
In the universe there are many black holes with different mass, size and gravitational force. Based on this black holes could be classified into 4 types -
- Micro black hole
- Stellar black hole
- Intermediate black hole
- Supermassive black hole
Micro black hole
Micro black hole also called as mini black holes, they are smallest black hole which could be formed. They have a millimeter size but have a mass which is almost as much as earth. They are still hypothetical and no such black holes are found till now. This idea was proposed by Stephen hawking.
Stellar black hole
Stellar black holes are black holes which are formed by the Hypernova of a star having around 5 to 10 solar masses. They have a radius of around 30 km. The stellar black hole is the most common black hole in the universe as most of the massive stars in the universe have 5-10 solar masses only.
Intermediate black hole
Intermediate black holes are formed after the hypernova of a giant star which has a mass of around 102-105 solar masses (1 solar mass means 1.989×1030 kg). Such a giant black hole has the capacity to destroy the entire solar system within seconds. There are many intermediate black holes present in the Milky way.
Supermassive black hole
Supermassive black holes are the largest black hole present in the universe . They have a mass up to 105-1010 solar masses, this means that they have mass of million or billion times the mass of the sun. This kind of black hole is super rare.
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| Supermassive black hole, Image source : India today |
The stars from which they are formed are from the beginning of the universe. Such kinds of supermassive black holes help in the formation of galaxies. And at the galactic centre of every galaxy there is a supermassive black hole present.
What is inside of a black hole ?
The truth is, we don't really know about it. Some scientists believe that the laws of physics as we understand break down inside a black hole, and that there may be other dimensions or universes beyond the event horizon. Others believe that the universe could be a simulation and the black hole could be a gateway to another reality.
Can black holes emit light?
Answer is that black hole does not emit light, But the matter around the black emit light. When matter comes near a black hole It first enters the accretion disc. Due to such a strong gravity it starts to spin around the black hole very fast which starts to increase its temperature.
As the temperature rises, eventually it starts to transform it into plasma. This plasma then emits light. Thus making a ring around black hole which is visible to us. This ring around the black hole helps us to find black hole.
What black hole emit ?
Until 1979 it was thought that black holes lived forever and never died. But then an astrologist Stephen Hawking put up a theory which followed every physics law and helped astrologists to understand how a black hole emits radiation and named the radiation the Hawking radiation.
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| Hawking radiation, Image source : Sky at night |
Before understanding how a black hole emit Hawking radiation you need to understand what are virtual particle, in space according to quantum world there is always a birth of one positive and negative particle which is different than other normal particle. This positive and negative particle collide with each other disappear this pair of positive and negative particle are called virtual particle.
When such virtual particles are formed near the event horizon. The negative particle gets inside the black hole as having less energy and the positive particle escapes. As the positive particle escapes, the viewer outside the black hole sees that positive particles are coming out of black hole. These positive particles are called the Hawking radiation.
Which black hole is at the centre of the Milky way ?
The super massive black hole helps in the formation of galaxies as its gravity helps to hold the entire galaxy together. And every galaxy in the universe has a supermassive black hole at its galactic centre. In our galaxy Milky way our galactic central super massive black hole is the Sagittarius A. It has a radius of 12 million km and has a mass of around 4.1 million solar masses.
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| Sagittarius A, Image source : Gigazine |
Which is the biggest black hole?
The largest black hole in the known universe and observable universe is located in the galaxy Holm 15A. The name of this supermassive black hole is TON 618. This black hole is 700 million light year away from us. And has mass of around 66 billion times the mass of sun. It has a diameter of around 390 billion km.
How black holes die ?
Until 1979 it was thought that the black hole never died and remained forever. But after Stephen Hawking found Hawking radiation, it was proved that black holes also die. As the Hawking radiation is emitted by the black hole. The black hole starts to lose energy and mass.
As the Hawking radiation starts to get released by black hole it starts to evaporate and eventually the black disappears. But this is a very lengthy and long process and a black hole with 1 solar mass takes up to 1064 years to evaporate completely.
Conclusion
So this was all for today. We hope that you would have learned something new about Black Hole. Important points of the post were -
- A cosmic body with such a strong gravitational pull that even light can’t escape is the Black hole.
- The closest black hole to earth is Gaia BH1.
- The black part of the black hole is the event horizon.
- The singularity has infinite mass, infinite density and space and time is completely distorted.
- Accretion disc is the outermost part black hole
- In the accretion disc matter close to black hole, due to strong gravity and high temperature starts to turn in plasma state and releases photons.
- Supermassive black holes help in the formation of galaxies.
- Stephen Hawking found Hawking radiation, it was proved that black holes also die. As the Hawking radiation is emitted by the black hole.
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