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Black hole

  2. 2. 1ST OF ALL LET US ANSWER SOME FREQUENTLY ASKED QUESTIONS AND BASIC QUERIES ABOUT THIS MYSTERY. 1. What is a BLACK HOLE actually? A black hole is a region in space where gravity pulls so much that even light can not get out. The gravity is so strong because matter has been squeezed into a tiny space. This can happen when a star is dying. Because no light can get out, people can't see black holes. They are invisible. Space telescopes with special tools can help find black holes. The special tools can see how stars that are very close to black holes act differently than other stars.
  3. 3. A BLACK HOLE
  4. 4. 2.HOW BIG ARE BLACK HOLES?  Black holes can be big or small. Scientists think the smallest black holes are as small as just one atom. These black holes are very tiny but have the mass of a large mountain.  Stellar black holes= Its mass can be up to 20 times more than the mass of the sun.  Super massive black holes=The largest black holes have masses that are more than 1 million suns together. The super massive black hole at the centre of the Milky Way galaxy is called Sagittarius A. It has a mass equal to about 4 million suns and would fit inside a very large ball that could hold a few million Earths.
  5. 5. How Do Black Holes Form?  Scientists think the smallest black holes formed when the universe began. Stellar black holes are made when the center of a very big star falls in upon itself, or collapses. When this happens, it causes a supernova. A supernova is an exploding star that blasts part of the star into space. Scientists think super massive black holes were made at the same time as the galaxy they are in.
  6. 6. Formation of a black hole Stage wise formation of a black hole
  7. 7. If Black Holes Are "Black," How Do Scientists Know They Are There? A black hole can not be seen because strong gravity pulls all of the light into the middle of the black hole. But scientists can see how the strong gravity affects the stars and gas around the black hole. Scientists can study stars to find out if they are flying around, or orbiting, a black hole. When a black hole and a star are close together, high-energy light is made. This kind of light can not be seen with human eyes. Scientists use satellites and telescopes in space to see the high-energy light.
  8. 8. Why light can not escape a Black hole?  We know on earth that if anything is to escape the earth, it should be projected at a speed of 11.8 km/sec. This means that the escape velocity earth is 11.8 km/sec.  But in the case of black hole the scenario is entirely different. Due to its huge gravitational pull the escape velocity from a black hole is even greater than the SPEED OF LIGHT which means greater than 3*10^8 m/sec. Hence we can conclude that even light cannot escape from it & thus a black hole appears BLACK.
  9. 9. Why do two black holes come closer and merge?  More than half of the stars in a galaxy are double stars and there is every possibility that both the stars in a binary would become black holes!  According to classical electro-dynamics, accelerated electric charges radiate electro magnetic waves and thereby lose energy similar to gravitational bodies.  Thus black holes have a great tendency to merge with each other.
  10. 10. Black hole submergers!
  11. 11. Stages in black hole mergers.  The final merger of two black holes can be divided into 3 stages: 1. Inspiral……2. Merger….3. ringdown  Inspiral stage= in this stage, the holes are relatively far apart and can be considered as point masses. As these go on radiating gravitational waves, their orbits go on contracting and, in accordance with Kepler’s 3rd law of planetory motion.
  12. 12. Merger stage!  When the two holes come very close and only a few final orbits are left, the holes leave their orbits and plunge together in a rapidly shrinking spiral.  The event horizons of the two merge to form a single highly distorted black hole.
  13. 13. Ringdown stage!  The distorted single black hole that has resulted from the merger radiates away all its distortions in the form of gravitational waves and becomes a smooth, symmetrical, rotating black hole.  The process is similar to what happens when a bell is struck by a hammer, the bell radiates all its distortions as sound waves and ringsdown and so the name ringdown.
  14. 14. Types of black holes…  1. Stellar black holes= these have masses about 3 to 30 solar masses and which are formed due to exhaustion of thermal nuclear fuels.  2. Intermediate masses= these have masses equal to 10^2 to 10^3 solar masses which form from merger of small black holes in the centers of dense stellar clusters.  3. Supermassive black holes= these have masses equal to 10^4 to 10^10 solar masses which are found in the center of most galaxies.
  15. 15. Could a Black Hole Destroy Earth?  Black holes do not go around in space eating stars, moons and planets. Earth will not fall into a black hole because no black hole is close enough to the solar system for Earth to do that.  Even if a black hole the same mass as the sun were to take the place of the sun, Earth still would not fall in. The black hole would have the same gravity as the sun. Earth and the other planets would orbit the black hole as they orbit the sun now. The sun will never turn into a black hole. The sun is not a big enough star to make a black hole.