Black Hole is a very interesting topic for all generations of people. Black Hole is not only an object but also an astronomical event. There is always the question, what is black hole ?

As for the answer black hole is an astronomical object with a dense and concentrated mass. The common theory about forming a black hole is known to all. The theory suggests, when the gravitational force of a star is so much compared to the force inside the star or perhaps the inside force has not enough power to hold on against its own gravitational force, it forms a black hole. It’s mainly true to stellar black holes. When this kind of event happens, it is safe to say that the star is close to ending its life.  

The gravitational force is so much forcing the star to become a black hole. The famous theory of relativity by Einstein is known to all. One part of the theory describes how gravity works ? Due to the surface of the space or perhaps the space time fabric curvature we feel gravity. 

According to the theory, the object that makes the dipper curve has the most powerful gravitational force. Gravity relays on mass. [ F = Gm1m2/r2 ] As the star gets more compressed and more dense, The mass of the star increases as well. That’s why black holes have the most gravitational force in the whole universe.  

There are mainly three types of black hole:

• Stellar Black Hole
• Supermassive Black Hole
• Intermediate Mass Black Hole 

We are gonna discuss the first two types of Black Hole in this blog today.

Different parts of a black hole:

1. Singularity
2. Event Horizon
3. Schwarzschild Radius
4. Photon Sphere 
5. ISCO
6. Accretion Disk

Singularity: There is not so much to talk about, but It is the center of a black hole. It is the most dense part of the black hole. 

Event Horizon:    Keeping the singularity in the center, think of a circle. Or perhaps the core of a Black hole is called Event Horizon. The event horizon is a boundary in spacetime beyond which nothing can escape. In simpler terms, the event horizon is the “point of no return” .

Schwarzschild Radius :  The Schwarzschild Radius is the radius of the event horizon of a non rotating black hole. It represents the critical distance from the center of the mass. There is a mathematical equation, which is [ Rs = 2GM/c2 ]

Where : 

• Rs = the Schwarzschild radius,
• G = the gravitational constant  
• M = the mass of the object 
• C = the speed of light 

This theory describes how much the object has to compass  to become a black hole. As an example, if the sun (with its current mass) were compressed to a radius of approximately 3 KM, it would become a black hole.

Photon Sphere :  There is a place where light can orbit the black hole. Of Course from the name ‘photon’ any one can understand there is something to do with light. In this condition there are two possible ways. For the light, if it crouches the photon sphere from the outside it will fall into the black hole. Another way is, if the light crouches the sphere from inside it has two possibilities. Whether the light will straightly begin to go to infinity or it will again come back to singularity. 

ISCO: It is a short form of Innermost stable circular orbit. It has the smallest radius at which a particle or object can maintain a stable circular orbit around the black hole. Within this radius, circular orbits become dynamically unstable, and any particle or object would spiral inwards toward the black hole. ISCO actually has no fixed place. It depends on the spine of the black hole. The faster the Black Hole spears the closer the ISCO will be and the slower the spine, the farther it’s away from the event horizon. 

Earlier I mentioned three types of black holes. I also mentioned I’m gonna describe the first two types of black hole. 

Stellar Black Hole: Stellar black holes are very common. I described how it forms in the beginning of the article. A stellar mass black hole typically ranges from around 3 to 100 times the sun. These black holes are much smaller than the super massive black hole.  

Supermassive Black Hole: These black holes are the largest type of black hole. These black holes are typically found in the center of galaxies. This ranges around millions of billions of times the mass of the sun.  This black holes have mass between 10^6 to 10^10 solar masses. Our galaxy has its own supermassive black hole in the center, It’s called SAGITTARIUS A*. Which is 4 million times heavier than the sun. Unfortunately there is no specific saying, how a supermassive black hole forms But there are several theories about it. But there are two renowned  theories.

1.  Small seed theory
2. Large  seed theory

Small seed theory: It says how a supermassive black hole forms from a seed black hole. According to the theory supermassive black holes originate from relatively small “seed” black holes that formed early in the universe’s history and gradually grow to their immense size over billions of years. Over time those seed black holes grow by accreting gas, dust and other matter from their surroundings. There are other ways like during galaxy forms, galaxies frequently merge.

In this kind of situation black holes at their centers may also merge, forming a larger black hole. There are also challenges about this theory. It does not explain how a seed black hole could grow to billions of solar masses in less than a billion years. Observations of quasars in the early universe show that supermassive black holes already existed when the universe was less than a billion years old. You might have a question. What is quasar? It will need another article to cover up. But for now it can be said, quasars are  glowing assertion disks of black holes where light, matter, molecules etc orbits. It creates so much friction and energy that it glows so much. 

How can quasars show whether the theory is correct or not? There is something called redshift and blueshift. When a light comes from so far away, the wave of light gets straight and converts to read light. It is called readshift. The light source is close, the wave of the light does not straight and convert to blue colour. It is called blueshift. It can be calculated, how old the light source actually is?  That’s how it can be said, how first the supermassive black hole had formed after the big bang. 

Large seed theory: Apparently these theories are quite similar. Large seed theory suggests, the supermassive black hole at the center of galaxies originated from unusually massive initial “seeds” that formed early in the universe. According to the theory there may be those large seeds that originated from large primordial black holes, which formed shortly after the big bang from density fluctuations in the early universe. 

Another possibility suggests large seeds come from the direct collapse of massive intermediate stars. This theory improves supermassive supermassive black holes better than small seed theory because there  are massive seeds that can attract  more surroundings like gas and dust etc. There is a possibility, it may merge with other black holes in a dense early  galaxy environment. This answers the question, how this seed black hole can grow that faster.

After the discovery of quasars and observing them at very high redshifts suggests the existence of billion solar mass  black holes less than a billion years after the big bang. Such rapid growth is more easily explained if those supermassive black holes started as large seeds. But  there are challenges to large seed theory too. 

 Large seeds might originate from the collapse of Population III stars (the first generation of stars). However, these stars require pristine, metal-free gas clouds, which became scarce as the universe evolved.

These theories are more detailed. I explained these theories in very short. If you want to know in details you can email me in the given email. I will make a specific article on that. 

Extra information: How the black hole was founded by humans.

1. Theoretical Foundations (18th Century)

• 1783: John Michell, an English natural philosopher, proposed the idea of a “dark star” with gravity so strong that light could not escape. This concept was an early precursor to black holes.
• 1796: Pierre-Simon Laplace independently proposed a similar idea in his book Exposition du Système du Monde.

2. General Relativity and the Schwarzschild Solution (20th Century)

• 1915: Albert Einstein published the theory of general relativity, which described how gravity could bend spacetime.
• 1916: Karl Schwarzschild provided the first exact solution to Einstein’s equations, describing what we now call a black hole (the “Schwarzschild radius”).

3. Name and Concept Formalized

• 1939: J. Robert Oppenheimer and Hartland Snyder described how massive stars could collapse into objects that would trap light, forming a “singularity.”
• 1967: Physicist John Archibald Wheeler popularized the term “black hole” during a public lecture.

4. First Observational Evidence

• 1964: X-ray emissions from the binary star system Cygnus X-1 were detected, suggesting the presence of a black hole. Cygnus X-1 became the first widely accepted black hole candidate.
• 1971: Cygnus X-1 was confirmed as a strong black hole candidate through additional studies of its X-ray emissions and companion star.

5. Direct Image of a Black Hole

• 2019: The Event Horizon Telescope (EHT) captured the first-ever image of a black hole’s shadow. This black hole is located in the center of the galaxy M87.

Back to Home