Search This Blog

Black Holes - Part 1: History, Indirect Detection and Types

"There is a difference between knowing the path and walking through it."

The above lines of the movie "The Matrix" are the gist of the pursuit of Scientific Community to see the Black Hole. 

Brief History:

Sir Albert Einstein came up with his Theory of General Relativity in year 1916 and provided the world with a new perception of the Universe. According to him the Space and Time together forms a 4 dimensional continuum called as Space-Time and the Gravity is just a effect of bending / formation of curves due to objects with mass / momentum. Though Sir Isaac Newton gave theory of Gravitation but his theory could not explain the reason of why Gravity exists or how the two heavy objects can detect the presence of each other for exerting Gravitational Force. Einstein's Theory explained it. He  also proposed that Light is also affected by Gravity. General Relativity theory provides a Differential Equation solving which different equations pops up and believe me, even after 100 years, the different postulates of his theory are being tested and are being found 100% correct. 

In the decade of 1920s, Schwarzschild came up with a solution using General Relativity and he deduced that if mass of an object is squeezed to a certain radius called as Schwarzschild radius as of formula r=2GM/c^2, then the Gravity/Bending of Space-Time Curvature around that object would be so strong that light would not be able to pass it and it would never reach back to the observer's eye, as a result the observer would never be able to see that object and hence the name "Black Hole" was given later to such objects. It was a sensational prediction and that time nobody believed even existence of such objects. 

In the later decades with more and more Physicists like Penrose, Stephen Hawkings and other Astronomers took interest in this object, the Celestial Bodies with similar properties as predicted for Black Holes were indirectly observed.  Indirectly observed means we detected effects of presence of such bodies that matches the properties of Black Holes. For Example:

Gravitational Lensing: Bending of light coming from a Galaxy behind a black hole which is in our sight of view.
Image result for gravitational lensing

Effects on the Motion of Celestial Bodies: By measuring the speed, angular momentum and mass of celestial bodies like Stars, Galaxies etc revolving around a Black Hole like body, the mass and radius of such body can be deduced and by using formulas derived from General Relativity, it can be easily established that such Black Hole like Body is actually a Black Hole. 

Image result for effect of black hole on motion of stars

What is a Black Hole:

An object so dense and having so strong Gravity that even Light can not surpass it. For example, if you squeeze the earth's mass into the size of a pea, that pea sized object will become Black Hole. It can not be seen as no electromagnetic radiation can come from inside of it.

Types of Black Hole:
  • Stellar Black Holes: One that has been formed by Collapse of a Star and having mass of a star (Usually more than 1.5 times that of Sun)
  • Super massive Black Holes: One that are having mass of millions of Suns and are usually found in the Centre of each Galaxy
Apart from that, Black Holes are also categorized on the basis of Spinning Black Holes and Non-Spinning Black Holes according to their properties - Spinning or no Spinning.

Next Post »