Journey Through the Cosmos: Exploring Black Holes & Dr. Stephen Hawking's Legacy.pptx

Title: Journey Through the Cosmos: Exploring Black Holes & Dr. Stephen Hawking's Legacy

Embark on a captivating journey through the depths of space and the brilliant mind of one of history's most renowned scientists, Dr. Stephen Hawking. In this enlightening presentation, we delve into the enigmatic phenomenon of Black Holes, their mysterious nature, and the groundbreaking discoveries that have shaped our understanding of the universe.

Unlock the secrets of these celestial wonders as we explore topics such as the fundamental question: What is a Black Hole? Delve into the gripping tale of their discovery and unravel the intricate process of their formation. From the mind-bending structure of Black Holes to the various types that exist across the cosmos, each slide unveils a new layer of cosmic intrigue.

But what happens if someone were to venture too close, falling into the gravitational abyss of a Black Hole? Discover the scientific speculation and theories that surround this captivating scenario, offering insight into the ultimate fate of such an intrepid explorer.

Moreover, journey through the extraordinary life and groundbreaking research of Dr. Stephen Hawking, a visionary whose contributions to theoretical physics revolutionized our understanding of the cosmos. Explore the trials and triumphs of his remarkable journey, from his early years to his groundbreaking work on Black Holes and beyond.

1. Topic Name :- Stusy on Black Hole and Dr. Stephen Hawking Biography.

2. Index Page:- What is a Black Hole? Discovery. Formation of Black Hole. Structure. Types of Black Hole. What If Someone Get Sucked Into Black Hole. Scientist's Opinions About Black Hole. Life of Stephen Hawking & Research. Page No- 1

3. 1 . What is a Black Hole? A region in space having a gravitational field so intense that no matter or radiation can escape. Black holes are some of the strangest and most fascinating objects in space. They're extremely dense, with such strong gravitational attraction that not even light can escape their grasp. The Milky Way could contain over 100 million black holes, though detecting these gluttonous beasts is very difficult. At the heart of the Milky Way lies a supermassive black hole — Sagittarius A* . The colossal structure is about 4 million times the mass of the sun and lies approximately 26,000 light-years away from Earth , according to a statement from NASA By the 1960s, researchers and scientists had finally agreed that not only theoretically, perhaps one day realistically, we’d be able to see black holes. Because these do exist in space. The term black hole was used for the first time by a magazine named “Science News Letter” in 1964. But only after 1967, the term gain popularity when physicist John Wheeler popularized it. The first image of a black hole was captured in 2019 by the Event Horizon Telescope (EHT) collaboration. The striking photo of the black hole at the center of the M87 galaxy 55 million light-years from Earth thrilled scientists around the world . [NASA] Page No- 2

4. 2. Discovery There are two parts of Einstein’s THEORY OF RELATIVITY . At first come the special theory of relativity.Special theory of relativity which was published by Einstein in 1905 tells us how speed influences time. If you are in a spaceship that is going very fast then time will be slow down for you, relative to the people not in the spaceship back on Earth. It is known as “Kinematic Time Dilation”. Not only speed, but even gravity can be reason of time dilation, which was shown by Einstein by his general theory of relativity. This was developed by him in 1915. He said that if you experience more gravitational force then time would slow down more for you. This is called “Gravitational Time Dilation”. He found that not only physical objects but also heat, sound and light can be affected by gravity. So, he thought that there can be objects in the universe which have such a high gravitation force that they can completely absorb light. But he presented his theory of general relativity the concept of black holes were merely theoretical back then. He knew that gravitation influences light that’s why this type of objects can be exist that can absorb light. But he didn’t know that there are actual black holes. A key point of his theory was that the speed of light limits gravitation influence. Page No- 3

5. That’s mean we cannot feel gravity’s force instantly, everywhere. It’s upper limit is the speed of light. It means the sun disappears suddenly then we can see it after eight minutes but Einstein said that the gravitational impact of disappearance of the sun we will also feel after 8 minutes. After Einstein many other scientists like S.Chandrashekar, Karl Schwarzschild, and Johannes Droste worked on the theory of relativity. There were many equations which were solved by them. And by getting to the solutions of these equations first time it was theoretically proven that things like black holes, do exist. Page No- 4

6. 3. Formation of Black Hole: - Primordial Black Holes are thought to have formed in the early universe , soon after the big bang . Scientists think Super Massive Black Holes Form at the same time as the galaxy they are in. This is why these types of Black Holes are known as the oldest Black Holes . [NASA] But the most common Black Hole, Stellar Black Hole have some different origin , they forms when a star uses all of its energy. A star gets its power my nuclear fusion reaction , where a helium (He) atom is made when two hydrogen (H) atoms are merged. And we can find gravity everywhere in the whole cosmos. These two main forces are applied in a star, where nuclear reaction tries to expand the star and gravity which tries to collapse the star inwards its own center. The radiation and the ligh t that is emitted by the star also apply pressure on the star outwards that is called “Radiation pressure”. The force of nuclear fusion reactions and the force of radiation pressure counteract the force of gravity to maintain the size and the shape of the star. So there is always a ‘tug of war’ like situation between nuclear fusion and gravity. But at the end days when the star cannot perform nuclear fusions in its own body it loses the radiation pressure and the force of nuclear fusion which tries to expand the star. And at the end when the gravity won properly then the star collapse into its own center with a huge explosion of radiation. Page No- 5

7. That can easily destroy any civilization of any planet which arrives into its way. The explosion called ‘‘ Nova ’’ or ‘ ’Super Nova ” depending on the scale of the blast. After the explosion the star leaves its small and intensely dense core which has almost the equal weight of the star. It is not mandatory that a star only transform into a Black Hole after its death. A star also can be a “White Dwarf” or a “Neutron Star” depending on its mass. That is why in 1931 our Indian-American scientist Subramanyan Chandrasekhar discovered that only few stars can be a Black Hole which has at least 1.5 times more mass than our Sun. He also proved that our Sun will never be a Black Hole. He developed the “ Chandrasekhar Limit Value ”. He said that the maximum mass of a White Dwarf can be 1.4 (more accurately 1.39) times of the mass of our Sun . Above which it cannot be stable and would turn into either a ‘ ’Neutron Star ’’ or a ‘ ’Black Hole ’’. But since our Sun is under this limit it will become a White Dwarf , instead of a Black Hole . What would happen if the Sun turns into Black Hole? Page No- 6

8. 4. Structures A Black Hole is a four-dimensional object with a spherical or nearly spherical shape that extends linearly through time, Main parts of a black hole are- Accretion Disc: When anything goes very closer of a black hole then due to high gravitation breaks into atomic particles and dust. And also for the gravity particles, gases, dusts and other particles starts revolving around the black hole with almost the speed of light . And due to high speed and friction , everything becomes hot and at last everything turns into plasma and creates a huge glowing ring around the Black Hole . And this plasma is also the reason why this ring emits UV Rays , X Rays , β Rays etc. In the film “ Interstellar ” we can see the Accretion disc in bright yellow and orange colours. But actually it is closer of blue light for the UV Rays . This structure is called Accretion Disc . We can see narrow ring of light upside and downside of a black hole . But actually the ring we can see is a part of Accretion disc . From where the light is coming to upside and downside is actually a part of the Accretion disc which is at the backside of the black hole . We can see it for the curvature of the light that is created for the high gravitation of black hole which creates a curve in the Space-Time fabric . [Getsetfly Science, Dhruv Rathhe, Wikipedia] Relativistic Jet: Super-massive Black Holes at the center of some active galaxies create powerful jets of radiation and particles (like photons ) travelling close to the speed of light . Attracted by strong gravity, matter falls toward the center of black hole as it feeds on the surrounding gas and dust. But instead of falling into the black hole , a small fraction of particles get accelerated to the speed almost as great as the speed of light and spawn out in two narrow beams along the axis of radiation of the black hole . These jets are believed to be the source the fastest traveling particles in the universe that is called “ Cosmic Rays ”. Gamma rays are also a part of this Relativistic Jet . Page No- 7

9. Photon Sphere: A photon sphere or photon circle is an area or region of space where gravity is so strong that photons are forced to travel in orbits, which is also sometimes called the last photon orbit. The radius of the photon sphere, which is also the lower bound for any stable orbit, is, for a Schwarzschild black hole. r=(3GM)/c 2 =3r s /2 [where G is the gravitational constant, M is the mass of the black hole, c is the speed of light in vacuum and r s is the Schwarzschild radius ( the radius of the event horizon)]. The equation entails that photon spheres can only exist in the space surrounding an extremely compact object (a black hole or possibly an “ultra-compact” neutron star) the photon sphere is located farther from the center of a black hole than the event horizon. Within the photon sphere, it is possible to imagine a photon that is emitted from the back of one’s head, orbiting the black hole, only then to be intercepted by the person’s eye, allowing him to see the back of his head. [Wikipedia]] Singularity: The very center of a black hole (or a white hole) where matter has collapsed in a region of infinite density is called Singularity. You can say that it is the processor of a cpu named black hole, which gives the main power to the system. Actually singularity is the remaining core of the star after its death. Event Horizon: In astrophysics, an event horizon is a boundary beyond which events can’t affect an observer. Wolfgang Rindler coined the term in 1950s. In the case of black hole event horizon is also a boundary, if anything enters into this, then nothing can come back including light. That’s why it is the nearest place of the singularity you can see light. You can detect an event horizon through a ring of light around the singularity of a black hole. Page No- 8

10. 5. Types of Black Hole Stellar:- It forms when the center of a very massive star collapse in upon itself. It is told that there are between 10 million to 1 billion Stellar Black Holes in our Galaxy. [NASA] Intermediate :- This type of Black Holes have the mass in the range 10 2 -10 5 solar masses , significantly more than Stellar Black Holes but less than 10 5 -10 9 solar mass Super-massive Black Holes. This type of Black Hole is hypothetical. [Wikipedia] Super-massive :- It is thought that there are Super-massive Black Holes in the center of any big galaxy. The Super-massive Black Hole which is at the center of our Milky Way is called “ Sagittarius A ”. [Wikipedia] Miniature/ Primordial :- This type of Black Holes is thought to have formed in the early universe, soon after the Big-bang. Miniature Black Holes also called Micro Black Holes or Quantum Mechanical Black Holes , are hypothetical tiny (<1 micron) Black Holes , for which quantum mechanical effects play an important role. The concept that Black Holes may exist that is smaller than stellar mass was introduced in 1971 by Stephen Hawking . [NASA, Wikipedia] Stellar Intermediate Super-massive Miniature/ Primordial Page No- 9

11. 6. What If Someone Get Scked Into Black Hole Page No- 10

12. 7 . Scientist's Opinions About Black Hole Page No- 11

13. Stephen Hawking was a great scientist who discovered the “Big-Bang” theory, which describes that how our whole was formed from a single particle. He became physically paralyzed in 1963 at the age of 21. He wrote a lot of books but his most famous books were “The Theory Of Everything”, “Black Holes: The Reith Lectures” & “A brief history of time”. In the book “A brief history of time” he explains a range of subjects in cosmology, including the Big Bang, black holes and light cones, to the non-specialist reader. His main goal is to give an overview of the subject, but he also attempts to explain some complex mathematics. He passed almost his whole life in the research of black hole. He started his research on the event horizon of black hole. He found that every information about the black hole is hided in its event horizon. But we are not able to interpret the information. That’s why he discovered a formula which was able to calculate the energy of the black hole by calculating the surface area of its event horizon. And by knowing the amount of energy of black hole we can find its mass by using the theory of relativity (e=mc 2 ) as mass is also a energy and by knowing the mass we can find the amount of energy. After that he discovered “Hawking Radiation” . In present time scientists are trying to discover the “Theory of Everything”, a theory which can combine “Quantum Mechanics” with Einstein’s “Theory of Relativity”. Black holes are normally studied by relativity but he applied quantum mechanics first time on a gravitational object, black hole. That’s how he discovered “Hawking Radiation”. He found that black holes always radiates a type of radiation outwards. This radiation postulates that if the black hole is radiating it means it is always loosing its mass and energy. And as it’s energy is proportional to the radius of its event horizon (Schwarzschild Radius), it means the radius of its event horizon is also decreasing, that means one day the schwarzschild radius will be zero and the black hole will be resolve in the space. But this event can only be happen if the black hole stop absorbing mass which compensate the radiation. 8. Life of Stephen Hawking & Research Page No- 12

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