According to NASA, there exists a region in the space which has so intense gravitational pull that even light and small particles cannot escape – the Black Holes. Gravity is so strong that the matter in the hole is squeezed into small space. Because light cannot leave the hole, so scientist cannot see it but the hole can be detected by special tools inside the space telescopes.

light and small particles cannot escape - the Black Holes

The presence of a black hole can also be predicted by its interaction with other matter such as with electromagnetic radiation. Black holes can vary in size. The smallest hole being observed is about the size of a single atom. But even the smallest hole contain mass equal to that of a mountain.

Predictions about black holes

John Michelle, in November 1784, wrote a letter in which he predicted the presence of a special body in space which is so massive that even light cannot escape it. He also speculated that the presence of such body will be possible by observing the interaction of that body with other objects surrounding it. Other scientists of that time were fascinated by Michelle’s idea but they argued that wave-like nature of light made the observations unclear.

Theory of Relativity developed by Albert Einstein in 1915 postulated that gravity does effect the wave-like behavior of light. According to this theory, there lies a region in the center of black hole where the gravitational pull becomes infinite and this area in the hole is named as “Singularity”. For a non-rotating black hole, singularity is found at a single point while for a rotating hole, this point is also non-static and exist in the form of a ring.

Formation of black holes

Due to the unique nature of a black hole, the question arises that whether a black hole actually exist or not, or they are barely the solution to Einstein’s Relative equations. Before getting into the discussion of formation of a black hole, it is important to understand “Event Horizon”. In simple words, an event horizon is boundary of black hole. It the borderline through which light and other particles can only pass inward, towards the center of hole. By the end of 1960, researchers found out that there is no obstacle in the formation of a black hole.


One kind of black hole is “Steller” which has a mass approximately 20 times greater than the mass of Sun. The number of black holes in the Milky Way Galaxy are unknown, but there may be hundreds of Steller in our galaxy. It is formed by the gravitational collapse of a massive star. Gravitational collapse is the contraction of an object due to its own force of gravity, which causes the mass of body to draw towards its interior. When this happens, it causes Supernova, which is regarded as the brightest explosion taking place in space.


The largest black hole are called “Supermassive” and have the mass of about 1 Million suns together. Scientist have proved that almost every galaxy contains at least one supermassive black hole in its center. Supermassive of our galaxy is called Sagittarius A and have mass equivalent of 4 Million suns and is about 250 Million Light Years away from Earth.  

Physical properties

After the formation of a black hole, it possesses only three physical properties including mass, charge and angular momentum. These are important in the sense that they are visible from the outside of a hole. For example a charged black hole will repel the other charged hole. It is also impossible to distinguish between black holes. If the two holes have the same values for the above three parameters, then it becomes impossible to differentiate between them.

How do scientist see black holes?

The question arises that if black hole is black then how does scientist see them? It is a fact because they draw light inside them that black holes are’not visible. But scientist have been able to see black holes by their interaction with the nearby stars and gases. A black hole exerts strong gravitational pull upon stars and other particles lying in its vicinity. Moreover, when a star and black hole come together, a very strong light is emitted in space. Specially designed telescopes and other devices see this light.

Can black holes be destructive for the earth?

The answer is simply No. Because black holes do not travel in space. No black hole is close enough to our solar system for the earth to fall into it. Even if a black hole having the same mass as the Sun would take place of Sun, the Earth and all the other planets in the solar system will still stay the same as they are now. Our sun is also a star. But  to form a black hole , the sun can never be converted into it, as it requires more mass.

NASA uses telescopes and satellites travelling in space to study and answer questions about black holes and other objects found in the universe.

By Razmia Sabahat Butt

I'm a student of BS Applied Biosciences at NUST, Islamabad.