The term itself "black hole" is quite recent. It has been invented in 1969 by an American scientist named John Wheeler. But in fact, the graphic description belonging to Wheeler represents an idea that is hundreds years old. At that time, there were two different theories on light. The first one belongs to Newton and it states that light is made of particles and the other one is that light is made of waves. Nowadays, we know that both theories are correct.
Because of the quantum physics' perspective on the particle/wave duality of light, this element can be seen both as a wave and as a particle. As far as the theory stating that light is made of waves is concerned, it wasn't very clear how light could respond to gravitation. But if light is made of particles, they would certainly be affected by gravitation in fact in the same way as planets, rockets and cannonballs are affected by this law of physics. At the beginning people believed that the particles of light moved at an infinite speed. But Roemer discovered that light's speed is finite and this showed that gravitation can have a major effect on it.
A member of the Cambridge College by the name of John Michell has written a work based on the above-mentioned theory, and published it in 1783 in the Philosophical Transactions of the London Royal Society magazine. In this writing, he has shown that a sufficiently massive and compact star could have such a strong gravity field that light cannot get out. Any light emitted by the surface of the star would be attracted back by the star's gravitational attraction before going too far. Michell actually suggested that there could be many stars like that one. Although we could not possibly see them because there light cannot reach us, we still could feel their gravitational attraction. These objects are now called black holes.
Light cannot however be regarded the same as cannonballs in Newton's theory of gravity, because it has a fixed speed. A constant theory regarding the way in which gravity affects light appeared only when Einstein proposed the generalized relativity in 1915. And even then it took quite a while until the implications of the theory for massive stars have been understood.
In order to understand the way in which a black hole can be formed, we first need to understand a star's cycle of life. A star is formed when a high quantity of gas (mostly hydrogen) starts to suffer from a collapse in itself because of its gravitational attraction. When it gets contracted, the gas atoms bump into each other more and more often and the gas gets warmer and warmer. Finally, the gas will get so hot that when the hydrogen atoms bump into each other they do not get too much separated from each other, but fusion and form the helium. The heat coming from this reaction is like a controlled explosion of a hydrogen bomb and it is the one making the star shine. This supplementary heat increases even more the pressure of the gas until it becomes enough in order to balance the gravitational attraction and the gas ceases to get contracted. It is much like a balloon.
So there is a balance between the pressures of the inner air trying to produce the filling up with air of the balloon. The stars will remain stable for a long time during which the heat coming out of the nuclear reactions balances the gravitational attraction. However, the star will finally remain out of hydrogen and other nuclear fuels. Paradoxically, the more stars have more fuel at the beginning, the sooner it ends. This happens because the bigger the star, the hotter it needs to be in order to consume its fuel.
Far from exhausting the subject, these are a few basic explanations on the fascinating topic of black holes' phenomenon. According to some recent news, American researchers have actually discovered the biggest black hole so far. It is placed at a distance of 50 million light years from Earth, and according to "Dailymail", it weighs as much as 6.8 billion suns.