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CONTENTS: <ul><li>INTRODUCTION </li></ul><ul><li>HISTORY </li></ul><ul><li>TYPES & SIZES </li></ul><ul><li>FORMATION & EVAPORATION </li></ul><ul><li>BIRTH & DEATH OF STARS </li></ul><ul><li>QUESTIONS RELATED TO BLACK HOLE </li></ul><ul><li>CONCLUSION </li></ul>
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INTRODUCTION TO BLACK HOLE Black holes are objects so dense that not even light can escape their gravity, and since nothing can travel faster than light, nothing can escape from inside a black hole.
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HISTORY OF BLACK HOLES <ul><li>In 1916, the concept was revived when German astrophysicist Karl Schwarzschild decided to compute the gravitational fields of stars using Einstein's new field equation. </li></ul><ul><li>Schwarzschild limited the complexity of the problem by assuming the star was perfectly spherical, gravitationally collapsed, and did not rotate. </li></ul><ul><li>His calculations yielded a solution aptly called a Schwarzschild singularity . </li></ul>
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STRUCTURE OF A BLACK HOLE <ul><ul><li>The point at the center of a black hole is called a singularity . </li></ul></ul><ul><li>That distance is called the event horizon . </li></ul>
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SIZES OF BLACK HOLE <ul><li>Black holes can be divided into several size categories: </li></ul><ul><li>Supermassive black holes - mass of the sun Intermediate-mass black holes , ultra-luminous X ray sources . </li></ul><ul><li>Stellar-mass black holes have masses ranging from about 1.5-3.0 to 15 solar masses. </li></ul><ul><li>Micro black holes ,. micro black hole or mini black hole formed during the Big Bang ( primordial black holes ), </li></ul>
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TYPES OF BLACK HOLES There are two types <ul><li>ROTATING </li></ul><ul><li>NON ROTATING </li></ul>
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BIRTH OF A STAR <ul><li>Due to supernova explosion, which results in formation of protostar , which is mainly composed of hydrogen molecules. </li></ul><ul><li>As the compression continues, the temperature increases, causing the hydrogen molecules to disintegrate into hydrogen atoms and finally electrons in hydrogen atoms separate from protons, or ionize. This is called a plasma . </li></ul><ul><li>As the compression continues, the centre becomes so hot that nuclear fusions begin. </li></ul><ul><li>A star is born. </li></ul>
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SUPERNOVAE EXPLOSION More massive stars tend to burn hotter and faster. Once all the nuclear fuel has been exhausted, such stars quickly collapse, shedding much of their mass in dramatic explosions called supernovae .
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Formation of stellar mass black holes <ul><li>Stellar-mass black holes are formed in two ways: </li></ul><ul><li>gravitational collapse </li></ul><ul><li>By collisions between neutron stars. </li></ul>
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Formation of smaller black holes <ul><li>The present black hole formation is through gravitational pull collapse. </li></ul><ul><li>Smallest mass which can collapse to form a black hole of approximately 1.5-3 times the mass of sun. </li></ul><ul><li>Smaller masses collapse to form white dwarf or neutron stars. </li></ul>
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Formation of larger black holes <ul><li>There are two main ways: </li></ul><ul><li>They act as "seeds“. </li></ul><ul><li>Due to gravitational attraction,produce a supergiant or hypergiant star and produces a supernova or hypernova and spends the rest of its existence as a black hole </li></ul>
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Evaporation of larger black holes <ul><li>Larger black holes evaporate . </li></ul><ul><li>By Hawking evaporation . </li></ul>
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HOW TO DETECT <ul><li>An artist view taken from the Hubble Space Telescope website showing an accretion disk around the black hole. The friction from the gas generates a massive amount of heat. The heated gas emits X-rays </li></ul>
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Black holes and Earth <ul><li>Black holes are sometimes listed among the most serious potential threats to Earth and humanity. </li></ul><ul><li>A naturally-produced black hole could pass through our Solar System. </li></ul><ul><li>Although it is purely hypothetical, a large particle accelerator might produce a micro black hole , and if this escaped it could gradually eat the whole of the Earth. </li></ul>
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HOW BIG IS A BLACK HOLE <ul><li>It depends upon mass and size of the star . </li></ul><ul><li>A typical mass for such a stellar black hole would be about 10 times the mass of the Sun, or about 10^{31} kilograms. </li></ul>
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If a black hole existed, would it suck up all the matter in the Universe? <ul><li>A black hole has a "horizon," which means a region from which you can't escape. </li></ul><ul><li>If you cross the horizon, you're doomed to eventually hit the singularity. But as long as you stay outside of the horizon, you can avoid getting sucked in. </li></ul>
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What if the Sun became a black hole? <ul><li>Only stars that weigh considerably more than the Sun end their lives as black holes. </li></ul><ul><li>The Sun is going to stay roughly the way it is for another five billion years or so. </li></ul><ul><li>it becomes red giant star, during which time it will expand to engulf the planets Mercury and Venus, and make life quite uncomfortable on Earth </li></ul><ul><li>very dark and very cold around earth </li></ul>
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Is there any evidence that black holes exist? --------------------------------------------- <ul><li>Yes, there is an indirect evidence that black holes exist. </li></ul>
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CONCLUSION <ul><li>WHY WE STUDY BLACK HOLES? </li></ul><ul><li>HUMAN CUROSITY </li></ul><ul><li>GRAVITATIONAL WAVES. </li></ul>