What is a Black Hole? [With Images and Facts]

Black hole is anything but an empty space. It is a great amount of matter packed in a very small space. So here we are going to discuss about some black hole facts and other interesting information about them.

The image of the Black Hole, recently given by the scientists for the first time.

A black hole is a cosmic body exhibiting such strong gravitational force that nothing, not even light, can escape it. Most of the black holes are can be formed at the end of the life cycle of a star’s life. Some of the black holes are formed when a massive star dies.

Studying about the black hole interests scientists and other people alike. It can be explained through the Theory of General Relativity, given by Albert Einstein. So if you are interested in knowing about black holes, such as some facts, theory, types, etc. you can read the guide we have provided you. We have added some related images along with the topics so that it becomes more interesting and informative for you to understand a particular topic.

Event Horizon- The Theory of General Relativity

Black holes have been there since the universe was formed. The black holes, much like their name, are dark and invisible, due to the fact that no light can escape it. But using space telescopes with special instruments, they can be viewed. The boundary from which light, or any matter, cannot escape, is called the event horizon. It can be also called a point of no return since the gravitational pull is so strong that escape of anything is impossible. The escape velocity at the event horizon is equal to the speed of light. The Theory of Relativity states that nothing can travel faster than the speed of light. Hence nothing inside the event horizon can ever cross it and escape its boundary. If you were an observer of the event, if an object approaches the event horizon, it would appear to slow down and does not quite pass the horizon.

How Is A Black Hole Formed

A black hole can be formed at the end of the life cycle of a star. It can also be formed at the death of a massive star. A star with 20 times mass greater than our Sun is capable of forming a black hole at its dying stage.

During the normal life stages of a cycle, the outward pressure of gravity pulling in and the inward pressure from the core constantly creates some pressure. during much of a star’s life stage, the gravity and pressure balance each other exactly. Hence a star remains stable. However, when the core of the star runs out of nuclear fuel, the outward pressure becomes much more and thus the core gets compressed even further. The denser the core of a star, the stronger is the gravitational force and hence it collapses under its own weight.

In case of small stars, when the nuclear fuel of the star is about to exhaust, this star expels most of its outer material, thus becoming a planetary nebula. This results in its core becoming extremely hot, exceeding 100,000 Kelvin. This stage might last for the next few billion years or so. After that, the star dies down peacefully. This type of star is called white dwarf.

When a very massive star explodes, a violent explosion takes place in space, expelling out the outer part of the star into space. The core completely collapses under its own weight. This kind of massive explosion leads to the formation of stellar black holes. 

A supermassive black hole is present at the centre of almost all the large galaxies. It is the largest kind of black hole, with the size of about hundreds to thousands, to even billion times that of the mass of our Sun.

Who Discovered The Black Holes

The idea of black holes was first proposed way back in 1784 when an English astronomer and clergyman John Mitchell conjectured that there might be body so massive that would have escape velocity greater than light.

In 1925, Albert Einstein gave his Theory of General Relativity, which defined gravity as the geometric property within space and time. Only a few months later, in 1916, Karl Schwarzschild gave the solution to Einstein’s field equation that characterised and incorporated the existence of a black hole. Although it was formally recognised and interpreted as being a region in space from which nothing can escape by David Finkelstein in 1958.

Black holes were predicted through the Theory of General Relativity given by Einstein. It proved that when a massive star dies, a dense remnant core remains in space.

Scientists were first able to unveil a picture of a black hole on April 10, 2019. Here is a video explaining black holes and why it is important

Types Of Black Holes

Image of a Supernova

 

Although black holes look similar when observed, what differentiates them is their characteristics or properties. The three characteristic properties which differentiate a black hole from each other are:

  • its core density or mass
  •  its spin (the speed at which it rotates around an axis)
  • its electrical charge

Astronomers have been able to measure the mass of the black holes by studying the properties of the materials around them. Till now, they have been able to discover two types of black holes, i.e., stellar mass black holes and supermassive black holes. 

A stellar mass black hole forms due to the gravitational collapse of the core of a massive star under its own weight. They have a mass ranging from 5-10 times of our Sun.

Image of a Stellar Black Hole

A supermassive black hole is the biggest back hole that has been discovered yet. It is likely to exist at the centre of most of the large galaxies. How these supermassive black holes are formed remains a matter of research for the scientists even now. The scientists agree that once a black hole is placed at the centre of a galaxy, it can gain size by accretion (or the accumulation of particles around through gravitational force) of matter and merging with other black holes. These black holes have a mass equivalent to billions of suns.

Image of a Supermassive Black Hole

 

Image of Sagittarius A, a bright and compact astronomical radio source at the centre of our Milky Way Galaxy

 

Here we have provided you with a video, so you can understand about the type of black holes better.

What Is The Black Hole Theory?

 

The period between 1950s-1970s was called the “Golden Age” in Science, since during this period many scientists made an extensive research on the Theory of General relativity and made some important discoveries about black holes in this regard. Let us now get to some of the important theories of black holes which have been given by scientists till now:

Schwarzschild Black Hole

In 1916, Karl Schwarzschild gave the solution to Einstein’s field equations, dealing with the gravitational force outside a spherical mass. It states that the electrical charge, angular momentum, universal cosmological constant are all zero. The Scwarzchild’s Black Hole, named after the scientist, is the simplest type of black hole. It is characterized by a black hole with a spherical boundary, called the event horizon.

Kerr’s Geometry or Metric

In 1963, New Zeland physicist Roy Kerr who gave Kerr geometry, an exact solution to Einstein’s field equation of General Relativity. The Kerr Metric or Kerr Geometry proposed by him can be used to calculate the gravitational field outside an unchanging massive rotating object, like a rotating black hole. So the Kerr’s metric predicted the spinning black holes before they were actually discovered by the scientists.

Hawking-Penrose Theorem of Singularity

Another English Mathematician and physicist, Roger Penrose made a contribution to the mathematical physics of General Relativity and Cosmology. In the late 1960’s, Penrose, along with Stephen Hawkings went on to apply a complex mathematical problem derived from Einstein’s General Theory of Relativity to find proof for the singularity thesis first given by Hawkings. Their theory provided sufficient calculations to prove that singularities existed in gravitational spacetime, and it was not a mathematical feature which is probable only in some special situations. It is in fact, a generic feature of general relativity.

Here we have provided you with a video explaining the Stephen Hawking’s Theory of Black Hole:

What Is Black Hole Made Of

The question that what is a black hole made up of, and what is inside a black hole, has been intriguing scientists and people in general. These odd and massive objects in space appear to be invisible and just a mathematical curiosity until the research done in 1960’s showed that they were generic derivations of the Theory of General Relativity.

Black Holes are really the most intriguing objects of the Universe, their sizes vary a lot, depending upon the situations they were created in. Scientists have found out that the tiniest of the black hole is just about the size of an atom. On the other hand, the biggest black hole, the supermassive black holes, can have a mass of more than 1 billion Suns together.

Black holes are the remnants of dying stars those which were roughly 20 times bigger than our own star- the Sun. Stars are made up of nuclear matter, like Hydrogen, Helium and other elements, so its mass becomes hundreds and thousands of times than the Earth. This huge mass produces great amount of gravitational forces which constantly opposes the inwardly forces of the nuclear reactions from the core of the star. When the star runs out of the nuclear fuel, a huge explosion takes place, throwing away the outer remnants of the star into space. What remains is a supernova made of gas and dust. If the core of this supernova is more than 2.4 times the mass of our Sun, then its giant gravitational pull squeezes all the elements into such tiny matter until all the matter have zero size. Hence the black holes are infinitely dense, so much so that no atoms can exist there.

Conclusion

Black Holes are like great jigsaw puzzles of the Universe which the scientists are still trying to solve. These odd objects have been defined by the Theory of General Relativity, but scientists still don’t know what goes inside them. We hope you found this article interesting and informative, and it could satisfy your curiosity regarding the Balck Holes.

 

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