What is a Black Hole?
Black hole is a cosmic body that has an extremely intense gravity from which nothing can escape from it. The death of a massive star created the black holes. During the death of a massive star, the stars get exhausted by the internal thermonuclear fuels in its core and then the core becomes unstable and gravitationally collapses inward. Meanwhile, the star’s outer layer was blown away. Inside the black hole, the dying star experiences the crushing weight and it reaches the point of zero volume and infinite density. This state is known as singularity.
This article clearly explains what is a black hole, black hole types, how are black holes formed, where is black hole, facts about the black hole in detail.
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The above image shows the appearance of M87* black hole from the earth in different periods.
About Black Hole Theory
In 1915, Albert Einstein published the general theory of relativity, in which he described the structure of a black hole and created the black hole theory. According to his black hole theory, the centre of a black hole is singular and it can hide the object’s surface in the event horizon. As the escape velocity inside the event horizon is more the speed of light, even a ray of light cannot escape from the black hole into space. Here, the velocity which is essential for a matter to jump from the gravitational field of a cosmic object is known as escape velocity.
In 1916, the German astronomer Karl Schwarzschild named the radius of the event horizon as Schwarzschild radius by predicting the collapsed stellar bodies, which emit no radiation. The size of the Schwarzschild radius is directly proportional to the mass of the collapsing star. According to the black hole theory, the mass of the black hole is ten times greater than the sun and its radius must be 30 km (18.6 miles).
Types of Black Holes
The black holes are of four types. They are stellar, supermassive, miniature and intermediate. In that, the stellar death is the most commonly known black hole. It was mainly formed when the stars reached the end of their lives, most of the stars will expand, lose their mass and get cool to form a white draft. Here, the live stars are 10 to 20 times more massive than the sun. So, in the end, it becomes either super-dense neutron stars or so-called stellar-mass black holes.
How Are Black Holes Formed?
The black holes are mainly formed when the massive stars, whose mass are more than three solar masses, attain the end of their lives. The stars with less mass will result in less compressed bodies like white dwarfs or neutron stars.
Black Hole Facts
Usually, the black hole cannot be observed directly by considering its size or by its characteristics like it cannot emit light. The black hole can be mainly observed by enormous gravitational fields on nearby matter. For example, if a black hole is a member of a binary star system then the matter enters into it creates a companion and gets intense heat and radiates X-rays before entering into the event horizon of the black hole, further the object disappears forever. In 1971, Cygnus X-1 is a black hole that belongs to the binary X-ray system was identified, whose mass is 14.8 times of the sun and also it can revolve about one another in the period of 5.6 days.
Some of the black holes are of a non stellar origin. Many astronomers made research on the large volume of interstellar gases that are collected from the universe and collapsed it with the supermassive black hole. Here, the mass of gas falls rapidly into a black hole and provides 100 times more energy than the energy released during nuclear fusion. While millions or billions of solar masses of interstellar gas collapse under gravitational force, it creates large black holes and produces enormous energy in certain galactic systems.
The best example of such a supermassive black hole is Sagittarius A*. The Sagittarius A* is located at the centre of the Milky way galaxy. Its mass is 4,000,000 times more than the sun. American astronomer Andrea Ghez and German astronomer Reinhard Genzel did research on this observation and received a Nobel prize for physics in 2020. Many astronomers even found supermassive black holes in the other galaxies.
In 2017, The event horizon telescope captured the image of the supermassive black hole, which is located at the centre of the M87 galaxy, whose mass is six and half billion more than the sun. But it is only 38 billion km away from the sun. The supermassive black hole image captured from the M87 galaxy was the first direct image of the black hole. The universe has many other large black holes, whose mass is 10 billion times the sun. These black holes have extremely high velocities and energy effects on gas swirling at the centre of NGC 3842 and NGC 4889, which are the galaxies located near the Milky Way.
British astrophysicist Stephen Hawking also researched the existence of a kind of non stellar black hole. According to the theory of Stephen Hawkings, the universe has numerous tiny black holes in space, whose mass is equal to or less than that of asteroids. These black holes were created during the big bang, which originated 13.8 billion years ago at an extremely high temperature and density. These black holes are called mini black holes.
How to Make a Black Hole?
Since no human or human-made objects could reach near the black hole, which is situated even 1,300 light-years near the earth. Scientists have reacted to an artificial black hole inside the lab with high velocity and gravitational force. They mainly developed to study the properties of the black hole. Technion- Israel Institute of Technology also carried out many experiments and proved the observations made by Stephen Hawking on the black hole.
This article explained what a black hole, black hole properties, facts, where is black hole in universe, the types of black holes and also described the mass of various black holes in the universe.
FAQs on Black Hole
1. What is a black hole in simple terms?
A black hole is a region in spacetime where gravity is so intense that nothing, not even light, can escape from it. This happens because matter has been squeezed into an incredibly small space. The boundary beyond which escape is impossible is called the event horizon.
2. How is a black hole formed according to physics?
Most common black holes, known as stellar-mass black holes, are formed from the remnants of a massive star. When a star at least 10 to 20 times more massive than our Sun exhausts its nuclear fuel, its core collapses under its own immense gravity. This collapse triggers a supernova explosion, and the remaining core implodes to form a black hole.
3. What are the different types of black holes known to exist?
Scientists have identified three main types of black holes based on their mass:
- Stellar-Mass Black Holes: These are a few times the mass of our Sun and are scattered throughout galaxies like our Milky Way.
- Supermassive Black Holes: These are the largest type, with masses millions or even billions of times that of the Sun. They are found at the centre of most large galaxies, including our own (Sagittarius A*).
- Intermediate-Mass Black Holes: This is a rarer, mid-sized category, with masses between stellar and supermassive black holes. Their formation is still an active area of research.
4. What is the significance of the 'event horizon'?
The event horizon is a crucial concept for understanding black holes. It isn't a physical surface but a mathematical boundary. It marks the 'point of no return'. Any object, including light, that crosses the event horizon is gravitationally trapped and cannot get out. The size of the event horizon, known as the Schwarzschild radius, depends on the black hole's mass.
5. If black holes are invisible, how do scientists provide evidence for their existence?
Since black holes emit no light, their existence is confirmed through indirect observation of their effects on nearby matter. Key methods include:
- Observing Stellar Orbits: Scientists track the movement of stars that appear to be orbiting an empty point in space, inferring the presence of a massive, invisible object.
- Detecting Accretion Disks: As matter is pulled towards a black hole, it forms a spinning disk called an accretion disk. The intense friction in this disk heats the matter to extreme temperatures, causing it to emit powerful X-rays that we can detect.
- Gravitational Lensing: A black hole's immense gravity can bend and magnify the light from objects located behind it, an effect predicted by Einstein's theory of relativity.
6. What exactly is the singularity inside a black hole?
According to the general theory of relativity, the singularity is the theoretical centre of a black hole. It is a one-dimensional point where the gravitational forces are infinitely strong and all the mass of the black hole is concentrated. At the singularity, density and spacetime curvature are infinite, and the known laws of physics cease to apply.
7. How does a black hole affect the passage of time?
A black hole drastically affects time due to an effect called gravitational time dilation, a core concept of Einstein's theory of general relativity. The stronger the gravitational field, the slower time passes. For an observer near a black hole's event horizon, time would move much more slowly compared to an observer far away. If one could somehow observe a clock falling into a black hole, it would appear to tick slower and slower, eventually seeming to freeze at the event horizon.
8. What is the key difference between a black hole and a neutron star?
Both black holes and neutron stars are remnants of massive stars, but they differ in their ultimate fate. A neutron star is incredibly dense, but its gravitational collapse is halted by neutron degeneracy pressure—a quantum mechanical effect. A black hole is formed when the stellar core is so massive that this pressure is overcome, and gravity crushes the object down to a singularity with no force to stop it.
9. Could a black hole ever pose a threat to Earth?
No, there is no known black hole that poses a threat to Earth. Black holes do not wander through space randomly swallowing worlds. The nearest known black hole is thousands of light-years away, far too distant to have any gravitational effect on our solar system. For a black hole to affect Earth, it would have to be extremely close to our solar system, and no such object exists.
10. Who first developed the theory of black holes?
The theoretical foundation for black holes was laid by Albert Einstein in his General Theory of Relativity in 1915. Shortly after, in 1916, Karl Schwarzschild found the first exact solution to Einstein's equations that described such an object. However, the term 'black hole' was not coined until 1967 by the physicist John Wheeler.
