Black Holes are considered the most mysterious objects in the universe. This article is aiming to explain these mysterious objects in a simple manner. The article includes the following topics.
- Newton's law of universal gravitation
- The Schwarzschild radius
- Birth and Death of a star
- How black holes formed in the universe
An out and out explanation for gravitation and blackholes came with Albert Einstein's theory of relativity but way before that, during the time of Newton's law of universal gravitation scientists and thinkers were curious about a place where the escape velocity is greater than the speed of light.
Even light can't escape from such a place. These imaginary worlds later are known as black holes. To understand why Issac Newton's contemporary scientists and thinkers were curious about such a place, we should understand the concept of Newton's law of universal gravitation and Escape velocity.
- Newton's law of universal gravitation
Newton's law of universal gravitation states that every object in the universe attracts each other. The attractional force between them is directly proportional to the product of their masses and it is inversely proportional to the square of the distance between them.
During the time of this law, the scientific communities were actively debating about the nature of light. Christiaan Huygens proposed the wave nature of light but the scientist includes Issac newton believed in the Corpuscular Theory of light which is considering light as particles.
Later scientists confirmed that light has dual nature and explained all of the phenomena related to light with this dual nature theory. But the scientist and thinkers at that period thought that the light should be influenced by gravitation if it behaves as a particle.
A widespread thought experiment of that time defining a celestial body that has escape velocity greater than the speed of light should attract light. We cannot detect these objects with our naked eye, we can only observe the influence of their gravity in nearby objects.
- The Schwarzschild radius
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| Equation of Escape velocity |
In the above equation of escape velocity v stands for the velocity or escape velocity and M is the mass of the celestial object, r is the radius of that object.
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| Arriving at Schwarzschild radius |
r is known as the Schwarzschild radius, which is defining the event horizon of a black hole. In other words, we can say that an object with a mass of M is shrunk into radius r it will behave like a black hole, even light cant escape from such objects.
G is the universal gravitational constant its value is 6.674 30 x 10-11 m3 kg-1 s-2 and C is the speed of light which is also a universal constant its value is 299792458 (3x10^8 m/s).
What is the minimum radius of the earth to act as a black hole?
Here we are going to find out what will be the size of the earth(radius of the event horizon) if it became a black hole. For that, we are substituting the value of the mass of the earth in the above equation.
The above calculation showing that the radius of the earth will be 8.8 mm if it acts as a black hole.
- Birth and Death of a star
A star is born in a gas cloud called a nebula, the gas atoms are united there due to the force of gravitation. The nature of gravity is that its magnitude will increase with the increase in mass.
At a particular point, nuclear fission will be started at these gas spheres, the pressure due to nuclear fission will give an outward push and gravity will pull it to the center at a particular point these forces attain an equilibrium and that equilibrium is known as hydrostatic equilibrium. This is the point where a star is born.
After billions of years, all of the hydrogen in the star is fussed into helium and its fission will come to an end. The gravity will get an upper hand at this point. the star will start collapsing into it due to its own gravity. This stage of a star is called a compact object.
The death process of a star starts from here, the future of the death star will be determined by its mass. It can beam a compact star or more familiarly known as a white dwarf and it can become a neutron star or the supermassive stars can become a black hole.
The mass that differentiating a white dwarf from a neutron star is known as Chandrashekar Limit. A star with has a mass of fewer than 1.4 times the mass of the sun will become a compact star or a white dwarf, a star with mass greater than Chandrashekar's limit will became a neutron star. Stars having a mass greater than 3 solar mass or three times the mass of the sun will become a Blackhole.
The explanation of the black hole is incomplete without Albert Einstein's General Theory of Relativity and Stephan Hawkin's theories on black holes. Both of these will be explained in another article in U4unispaze.
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