What is black hole? Detailed discussion of black holes.

Story Highlights
  • What is a black hole?
  • How are black holes created?
  • When does a star turn into a black hole?
  • Who Discovered Black Holes?
  • What is the structure of a black hole?
  • Why can't something come out of a black hole?
  • Can black holes be seen?
  • What is the religion of black holes?
  • Types of black holes
  • Where is the black hole?
  • Do we have black holes in our galaxy?
  • Is there a destruction of black holes?
  • What is the maximum lifespan of a black hole?
  • Capture the first image of a black hole as possible

Black hole! There is no one who likes science who doesn’t like the word thrill. For more than a century, the term seems to have woken up scientists. The monster in space is called this black hole. And not just scientists, it is also the center of interest for science-hungry people.

But we also have a lot of misconceptions about black holes. Again, many may know very little about the wonderful cosmic object. So today we will try to know the details of the black hole in the light of the most accurate information.

What is a black hole?

A black hole is a place in space where the force of gravity is so strong that nothing can come out of it. Even electromagnetic radiation, like light, cannot penetrate this force of attraction. Due to the excessive density of matter in the black hole, it can create this unusual gravitational force around it. Since no light can come out of here, we cannot see them with the naked eye. They are completely invisible.

However, space telescopes with special equipment help to detect black holes. Although they cannot be seen, Einstein’s famous theory of general relativity predicts that black holes may exist in space, and that any space with such a massive mass must distort the spacetime around it. Recently, based on this theory, it has been possible to capture the first image of a black hole. The area of ​​a black hole from which nothing can come out is called the event horizon. A black hole acts like an ideal black object, because it does not reflect any light.

How are black holes created?

Black holes are usually formed by the compression of a large star at its center. Energy is generated through nuclear fusion reactions in each star. Multiple hydrogen atoms form helium atoms through fusion reactions. The two hydrogen molecules combine with each other through nuclear fusion reactions to form a helium molecule that emits a lot of heat energy, light energy and various types of radioactive radiation. But when the stars run out of this nuclear fuel (hydrogen), their nuclear reactions stop, which turns the star into a dead star. Like all objects, these stars have gravitational forces.

At this time the stars below the Chandrasekhar boundary turn into White Dwarf or White Dwarf. This does not happen in the case of the stars above the Chandra Shekhar limit. Inside these large stars, there is a lot of matter left and a lot of gravitational balls. This creates a kind of centripetal compressive pressure. Thus gradually all the mass begins to compress towards the center. In order to equalize the external and internal pressure, they make a huge explosion and expel some of their inner parts with great speed towards the outside. This huge explosion is known as “supernova”. This explosion will cause the outer surface of the star to be thrown into space and the inner one to become a black hole.

When does a star turn into a black hole?

For a star to become a black hole, it must have sufficient mass. Normally, stars with a mass greater than 3 solar masses turn into black holes through supernova explosions. If a star has at least 3 solar masses before it dies, a mass contraction at its center can cause a supernova explosion and create a black hole.

If a star is large enough (more than 3 times the mass of our Sun) at the end of a star’s lifespan, it explodes through a supernova and becomes a stellar black hole. Whether a star dies or becomes a black hole or a white dwarf depends on its mass. This limit is called Chandrasekhar limit. The mass of a stellar black hole can range from 3 times the mass of the Sun to hundreds of times. The smallest stellar black hole ever found is 3.6 times the mass of the Sun, with a diameter of only 24 kilometers.

Again, sometimes a collision of two black holes results in a new black hole. A collision produces a special kind of wave called a gravitational wave. Einstein mentioned the existence of this wave about a hundred years ago, which has recently been proven to be correct.

Who Discovered Black Holes?

In 183, geologist John Michell published a research paper entitled Dark Stars. The subject of his research paper was “an object of enormous mass whose gravitational pull cannot escape even light waves”. From here, things get trickier, and this is where the true meaning of black holes comes in. Later, however, it was admitted to the science community as an irrational theory. A theory that nothing like light could come out seemed quite unreasonable to scientists. So the study of black holes gradually stopped.

But in 1917, Albert Einstein first came up with his famous “general theory of relativity”. His theory not only described the relationship between space, time, gravity, and matter, but also opened the door to the theoretical possibility of a particular event known to us as a black hole.

His theory changed the concept of the gravitational ball responsible for the attraction of two objects in the universe. According to him, an object will curve a space-time in the universe. The heavier an object, the greater its space-time curvature. And it is for this curvature that an object will pull another object around it towards itself which we know as the gravitational force. The point is that space-time will tell the object how much to bend, and space-time curvature will tell the object how to move.

Space time
Space time Curvature
Image Source: Nasa

After this extraordinary theory of his, the discussion about black holes started again.

Karl Schwarzschild, a German physicist and astronomer, first proposed the modern version of the black hole in 1917, with the correct solution of Einstein’s general relativity approximation.

Schwarzschild realized that it was possible to compress any mass to an infinitely small point. And if a mass can be compressed to a certain point, it will bend the spacetime around it much more. Since all mass will be concentrated at a certain point, its force of gravity will be enormous and nothing, not even photons of light, will be able to come out of this particular region. This specific region around the mass is called the Schwarzschild radius.

Theoretically, every cosmic object could be turned into a black hole and they would have a Schwarzschild radius and could be calculated. If the Sun’s mass were compressed to an infinitely small point, it would form a black hole with a radius equal to only 3 kilometers (about 2 miles).

Schwarzschild radius, rs = 2GM / c2


G = gravitational constant

M = mass of matter

c = speed of light

Similarly, calculating the Schwarzschild radius of the earth would be only a few millimeters, which is equal to a marble.

Einstein’s theory and Schwarzschild’s research brought a new tide to the study of black holes. Later, in the sixties of the last century, the research of British scientists John Wheeler, Stephen Hawking and Roger Penrose made this black hole the most popular subject in science. In 1986, John Wheeler named this wonderful black object Black Hole. Since then it has been known to us as a black hole. Later, in 1994, astronauts proved that there really is a black hole.

What is the structure of a black hole?

Black holes are considered to have three layers; External and internal events horizon and singularity.

The horizon or event horizon of a black hole is the layer or boundary around a black hole from which light cannot escape. Since the force of uninterrupted gravity extends across the event horizon, no particle can pass beyond the event horizon. Strong gravitational force traps it inside.

And the position in the center is singularity. This is the center of the black hole, where all the mass is concentrated. At this point the space-time curvature becomes infinite. Interestingly, the area of ​​this singularity is zero but the density is almost infinite. This is because almost the entire mass of a black hole is stored in its singularity. Interestingly, scientists have the least idea about this singularity. The idea, however, is that after breaking all the laws of physics at this point. There is no such thing as space tomorrow.

Why can’t something come out of a black hole?

The answer is very simple, force of gravity. The mass of a black hole is so large that it forms a ring of very strong gravitational force around it, making it impossible for anything to break through the force. Even if an object goes around it, it will disappear into the black hole due to this ball.

To better understand the matter, one needs to have an idea about escape velocity. If we consider the earth, we all know that if an object can be thrown upwards, it will surely return to the earth. But there is a limit to the speed of this throw. After a certain velocity, no object will ever return to Earth. This speed is the speed of release. That is, it is a velocity at which an object is thrown back and never returns to the ground. Earth’s release velocity is 11.2 km / sec. This means that if you can throw an object upwards at a speed of 11.2 km / s, it will penetrate the earth’s gravitational force and go into space.

In the case of spherical symmetry objects, the following equations determine the value of the velocity of release:

Escape Velocity, Ve = √ (2GM / r)

Therefore, the velocity of release depends on the mass of an object. And since the mass of a black hole is much higher, so is its release velocity. So much so that radiation like light does not allow anyone to come out through gravity.

Can black holes be seen?

Scientists do not see black holes the way they see stars and other objects in space. Because no light is reflected from it. However, it is possible to see it in some special way.

Black holes can affect the surrounding stars and dust. As the space around the black hole bends, the difference in the visibility of the surrounding stars and dust indicates the presence of the black hole. Again, black holes always emit a kind of radiation. Although no black holes can be seen, it is possible to detect all these radiations. By analyzing all these radiations, it is possible to identify the location of the black hole.

What is the religion of black holes?

Most supermassive black holes have mass, charge, and angular velocity. Normal static black holes, however, have mass but no electric charge or angular velocity. These black holes are known as Schwarzschild black holes, who invented this solution in 1916.

There is no observable difference in the gravitational field between the gravitational field of a black hole and any other similar spherical object. Black Hole’s “omnipresence” doctrine only applies to its event horizon; In the case of external gravity at greater distances, it is no different from any other object of the same mass.

Types of black holes

Black holes can be different. Some black holes are much larger in size, while others are relatively small. There are also variations in mass. According to scientists, even the smallest black hole can be the size of an atom. The following four types of black holes are mainly known;

1. Micro or mini black hole

2. Stella Blackhole

3. Intermediate Blackhole

4. Super Massive Blackhole

Micro or Mini Black Hole: These black holes are very small in size. However, their mass is not less at all. Their mass can be equal to a mountain. This type of black hole is called Micro Blackhole. Such black holes are completely theoretical. If objects with masses less than the mass of our Sun could be turned into black holes, they would become micro-black holes. They can be about the size of an atom. This type of black hole is also called Primordial Black Hole. Everything we know about this black hole is theoretical. In fact, astronomers have not yet seen such a black hole. Thinking mathematically, everything could turn into a black hole. For every object of a certain mass there is a certain radius in which the object can turn into a black hole. Previously defined as the Schwarzschild radius.

Stella Black Hole: It is believed that stella black holes can be formed in two different ways; Either a larger star falls directly into a blackhole without a supernova explosion or causes an explosion within a proto-neutron star. Stars ranging from 5 solar masses to 100 solar masses usually turn into stellar black holes. In some cases, however, the idea is that if a star is large enough (more than 3 times the mass of our Sun) at the end of its life span, it will explode through a supernova and become a stellar black hole. According to the Harvard-Smithsonian Center for Astrophysics, there are hundreds of millions of stellar black holes in the Milky Way.

Intermediate Black Hole: Once upon a time, black holes meant only stellar and super massive black holes. But a recent study has disproved this notion. Scientists have found a kind of massive black hole between Stellar and Super Massive. This type of black hole is called an intermediate mass black hole. This type of black hole can be 100 to 1 million times larger than our Sun. Like the Stellar Black Hole, they are born from the death of a massive star. On May 21, 2019, astronomers caught a gravitational wave in their antennae. At the junction of two stellar black holes at 65 and 75 solar eclipses, an intermediate black hole of 142 solar eclipses produced 8 gravitational waves. Finding an intermediate black hole is a difficult task. A 2016 study found that such black holes are also found in the center of small galaxies. Much of our knowledge about this type of black hole is still unclear.

Super Massive Black Hole: The radius of super massive black holes can be up to several hundred million kilometers. Their mass may be several thousand million times greater than the mass of our Sun. Several intermediate black holes in the central region of the galaxy could accidentally merge into one supermassive black hole.

The mass of supermassive black holes is usually greater than 0.1 to 1 million solar masses. However, according to some astronomers, those with a mass of at least 10 billion solar masses are called ultramassive black holes. According to scientists, the mass of a supermassive black hole could be up to 50 billion solar masses. Again, the occurrence of a supermassive black hole of 1 billion solar masses is comparable to the semi-major axis of the orbit of the planet Uranus, the radius of the horizon. Some features of supermassive black holes set them apart from low-mass black holes. The tidal force around their horizon is relatively weak.

On the basis of rotation, black holes can be divided into two parts:

1. Rotating or Spinning Black Hole: These are called rotating black holes because they have angular rotation. They revolve around their characters like the earth and the sun. In reality, all black holes are like this.

2. Non-rotating or non-spinning black holes: Black holes that are not in a rotating state are called non-rotating or non-rotating black holes. They do not exist in the real world. These are just theoretical.

Where is the black hole?

A black hole can be anywhere in a galaxy. Stellar black holes are scattered throughout a galaxy. However, at the center of each galaxy is a supamasive black hole. The entire galaxy revolves around this supermassive black hole. In some cases, the center of a small galaxy may have an intermediate black hole. However, large galaxies always have a supermassive black hole at the center.

Do we have black holes in our galaxy?

Yes, the Milky Way means that our galaxy also has black holes, again in the hundreds of millions. A study by the Harvard-Smithsonian Center for Astrophysics found that our Milky Way galaxy contains hundreds of millions of stellar black holes. According to NASA, there are about 10 million stellar black holes in our galaxy.

The super massive black hole in the center of our galaxy is called Sagittarius A *. The mass of this black hole is about 4 million times the mass of our Sun. According to scientists, the distance of this black hole from our solar system is about 26,000 light years. In 2019, the Paranal Space Observatory discovered a supermassive black hole at the center of the Holmberg 15A galaxy, about 700 light-years from the Milky Way, with a mass about 40 billion times the mass of the Sun and a Schwarzschild radius of 118.35 billion kilometers between Earth and the Sun! Its name is S50014 + 81.

Is there a destruction of black holes?

Yes, black holes are also destroyed. Black holes constantly emit radiation. In 1964, the famous physicist Stephen Hawking proved that black holes emit a constant stream of radiation. According to its name, this radiation is called Hawking Radiation.

He explained this radiation with the help of quantum fluctuations, a branch of quantum mechanics. According to quantum fluctuations, the vacuum of space is not actually zero. In this space, virtual particles are constantly being created and destroyed in pairs. One of them is a real particle and the other is an anti-particle. In a very short time after the creation of these objects and antiparticles, they merge with each other and become exhausted. When these virtual particles are generated near the event horizon of a black hole, these particles cannot be combined due to the gravitational force of the black hole. One of them is pulled by the black hole towards itself and the other is pushed outwards. The energy required to come out of this particle is provided by the black hole itself. This is the particle that we see coming out of the horizon of black holes in the form of radiation. This radiation is called Hawking Radiation. As a result of this radiation, the energy of the black hole gradually decreases. However, it is a very slow process. Thus radiation emissions result in the death of black holes. All of its mass is converted into energy through a massive explosion of black hole death. When a black hole dies depends on its mass. The larger the mass, the longer the black hole will last in the universe. For example, if the Eiffel Tower is turned into a black hole, it will only last a few seconds.

What is the maximum lifespan of a black hole?

Black holes are eroded by hawking radiation. Hawking radiation is a very slow process. That is why a black hole lasts a very long time. A black hole equal to the mass of the Sun takes about 10 ^ 67 years to decay. It will take 10 ^ 87 years for the Milky Way center black hole to decay. Again, the largest black hole in the universe will take about 10 ^ 100 years.

Capture the first image of a black hole as possible

The pictures of black holes that we see on TV, magazines, movies or online are all made through graphics. Prior to 2019, black holes were entirely dependent on research. We could not see the real picture. But on April 10, 2019, we first saw the real picture of a black hole. So let’s see how this impossible task was made possible.

1st image black hole
The very first image of a black hole
Image source: Nasa

In space, sometimes two black holes come very close to each other. In this state, the two black holes revolve in a spiral path centering on each other. In this way, the two black holes collided with each other at one time. This collision creates a gravitational wave. These waves can be detected from the earth with very sensitive instruments. Since black holes are completely dark, these phenomena are impossible to detect with the help of telescopes and other photo-detection devices used by astronomers.

We know that black holes are created by the destruction of a large star. At this time the temperature of the radiation emitted by the particles of the disk is billions of degrees. These revolve around the black hole at the speed of light and eventually merge.

Astronomers invented a special method to capture these radiation shots. They followed a method called interferometry and observed black holes in M6 and Sagittarius for two consecutive years. In this method 6 telescopes are placed in different parts of the world. The telescopes stretched from Hawaii to Arizona, from Mexico to Spain, and from Chile to the South Pole. The radiation collected from these telescopes is compiled in such a way that it appears to have been collected by a telescope. The image that this virtual telescope collects is a trace of particles emitted as electromagnetic radiation from the event horizon of a black hole. Most of these weak radiations are radio waves. Waves have had to travel trillions of kilometers to catch the eye of a telescope.

The HT team used their eight 1-millimeter wavelength radio telescopes to observe M87 and Sagittarius black holes at the center of our Milky Way for five nights in April 2017. The data that came out of the telescopes was so huge that it was not possible to transmit it over the Internet. These had to be recorded on a disc and shipped to the Massachusetts Institute of Technology in Boston. It took about a year to collect and send data from the South Pole. The size of the collected data was 4 petabytes. To process the data by supercomputers, the team of scientists had to work in shifts of 16 to 18 hours. However, the team of scientists did not release the results of the report obtained from Sagittarius. They just released the image of the M87 black hole. Because the picture quality of M87 was relatively good. And this is how we first see the real picture of a black hole.

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