BLACK HOLES by Aayush Sharma(includes einstein)

Black Holes, stephen hawking, birth of the universe, big bang, space warps and hyperspace models, lifecycle of a star, gravitational lensing, Ho the universe began, discoverability of various galaxies, Einstein' s theory of general relativity(an introduction), how time and space are influenced by the matter and energy in the unievrse, what will happen if you fall into a black hole, why is ime unidirectional, about the author, contents, etc

1. BLACK HOLES AAYUSH S

2. LIFECYCLE OF A STAR : FOR STARS WITH LESS MASS(THE SUN): The star is born from a cloud of nebulae  The star undergoes a main sequence of its life For a star of low mass, the outer layers expand, making it a red giant.  The outer layers expel, and it evolves into a planetary nebula  The remaining core becomes a white dwarf and then a black dwarf after cooling process FOR MORE MASSIVE STARS: The star is born from a cloud of nebulae  The main sequence is the same For more massive stars, they may undergo a supernova explosion  The core left behind collapses under gravity, leading to a neutron star formation  The remaining core may collapse under its own gravity to beyond a certain point, leading to a black hole formation.

3. GENERAL THEORY OF RELATIVITY To understand the working of Black Holes, the reader must know the basic idea behind Einstein' s theory of general relativity.  Before Einstein, Issac Newton proposed his theory of gravitation. However, a lot of things in this theory were incomplete, and many questions arose as to who is responsible for this force? The theory of relativity emerged as an answer to these incomplete questions. Einstein, in the year 1915, showed that gravity is not a force, instead it' s a bending or curvature of space-time(as shown in the background image) that objects or planets with a positive mass exhibit. Any object that has a definite mass will lead to the curvature of space, just as a marble kept on a plain surface of paper bends it inwards. This curvature is responsible for the force of gravity to emerge.  Einstein also showed that time is not absolute. In the presence of a high gravitational field, time itself dilates the more the fabric of space is bent. Let us observe in the next slide that how is time dilation caused:

4. TIME DIALATION EINSTEIN even went on to explain that time travel to the future is actually possible in presence of a gravitational field. He showed that when a light ray passes near the space-time bending made by the earth, or the sun, or a black hole, the light ray will also bend. However, another light ray passing on flat space will not experience curvature, and hence, it will not bend. Assuming that the distance of between points B-A and D-C (in this image) is the same, light has to travel a greater distance as it experiences bending which increases the distance between points D-C. This creates a paradox that both the distance and speed of light in the 2 situations is same, but the curved light ray will reach later than the plane light ray even if the speed of both the light rays are the same. Hence, to avoid this paradox, time slows down in case of the plane light ray, so that both the 2 light rays reach their end-points (A and C) together. (By application of the formula: speed=distance/time)

5. BLACK HOLES [EXPLANATION] As we saw in slide 2, when the core of a star collapses under its own gravity, it evolves into a black hole. Let us investigate how this happens: Anything in this beautiful universe needs energy to sustain. A star gets its fuel by conversion of hydrogen gas into helium by means of nuclear fusion chain-reactions inside its core. This is because hydrogen is the most abundant element in the universe, and the 2 main ingredients which cook up a star are itself: Hydrogen and Carbon. When this conversion takes place, a lot of energy is released. You can take the example of our sun, the sun is a star which when undergoes this reaction, produces energy in form of heat, light and solar energy that is captured by the solar panels of our school to provide electricity supply.  When a star exhausts its nuclear fuel, it has nothing to sustain itself in the universe, and begins to collapse as a result of its own gravity. The matter keeps on collapsing itself until a final point of infinite density is reached, what is called a space-time singularity which attains a gravitational pull so strong that not even light can escape from it. This region is then cut-off from the rest of the universe into a mysterious-state. These are what we now call, Black-Holes.