Black holes presentation

A basic information about black holes.

1. Black holes are objects of extreme density, w ith such strong gravitational attraction , that even light cannot escape from their grasp if it comes near enough. Definition

2. . Albert Einstein first predicted black holes in 1916 . The term ‘black hole’ was coined in 1969 by the American scientist John Wheeler.

3. What does a black hole look like? As gas falls into a black hole (perhaps coming from a nearby star), it will heat up and glow, becoming visible. Typically, not only visible light, but also more energetic photons like X-rays will be emitted by the gas. What we would expect to see (if our telescope s could "zoom-in" enough) would be a glowing rotating disk of material, with the black hole down a the center of the disk.

4. When a star burns through the last of its fuel, it may find itself collapsing . For smaller stars, the new core will be a neutron star or a white dwarf . But when a larger star collapses, it continues to fall in on itself to create a stellar black hole . How a star becomes a black hole?

5. Structure

6. The event horizon  of a black hole is the boundary around the mouth of the black hole where light loses its ability to escape. The inner region of a black hole, where its mass lies, is known as its  singularity , the single point in space-time where the mass of the black hole is concentrated.

7. Cygnus X-1

8. How the black holes tick? Black holes do n ot pull objects like a vacuum. Instead, objects fall into them .

9. Light is stationary. SINGULARITY EVENT HORIZON Light is pulled in. Light escapes. Inside the event horizon, space is being pulled faster than the speed of light. Black holes are incredibly massive, but cover only a small region. B ecause of the relationship between mass and gravity, this means they have an extremely powerful gravitational force .

10. One could well say of the event horizon what the poet Dante said of the entrance to Hell: objects can fall through the event horizon into the black hole, but nothing can ever get out of the black hole through the event horizon. The event horizon, the boundary of the region of space-time from which it is not possible to escape, acts rather like a one-way membrane around the black hole:

11. Chandrasekhar limit Subrahmanyan Chandrasekhar worked out how big a star could be and still support itself against its own gravity after it had used up all its fuel. Chandrasekhar limit = t he maximum possible mass of a stable cold star, above which it must collapse into a black hole. Chandrasekhar limit = about one and a half times the mass of the sun

12. Stephen Hawking’s example with the astronaut A n intrepid astronaut on the surface of the collapsing star, collapsing inward with it, sent a signal every second, according to his watch, to his spaceship orbiting about the star. As 11:00 approached his companions watching from the spaceship would find the intervals between successive signals from the astronaut getting longer and longer . They would have to wait only very slightly more than a second between the astronaut’s 10:59:58 signal and the one that he sent when his watch read 10:59:59, but they would have to wait forever for the 11:00 signal.

13. Stephen Hawking’s example with the astronaut The singularity will be always in the astronaut’s future , but never in his past .

14. Stephen Hawking is one of the scientists who have worked on the theories about the black holes. In ‘Brief history of time’ there is an interesting , but impossible idea (for near future) about the usage of the black hole’s power : Because of the radiation from the black holes in the form of X rays and gamma rays, black hole could run ten large power stations, if only we could harness its power. We can not have one of these black holes on the surface of the earth, and the only place to put such a black hole, in which one might use the energy that it emitted, would be in orbit around the earth – that is the impossible step for now. But, with the development of science and technology , in far future, people might find out much more about our universe, including the black holes, and would make them useful for their living.