Black Holes Contents--- <ul><li>History. </li></ul><ul><li>Formation of black holes. </li></ul><ul><li>Gravity deforms space time. </li></ul><ul><li>Gravity bends path of light. </li></ul><ul><li>Event horizon </li></ul><ul><li>Falling into black holes. </li></ul><ul><li>Rotating black holes. </li></ul><ul><li>Techniques </li></ul><ul><li>References </li></ul>
History-- The idea of preventing light from escaping as described by general theory of relativity was given by John Michelle. Even the British astronomer Pierre -Simon Laplace came with the same conclusion.
The intense gravitational field left when a giant star collapses. It is called a black hole because not even light can escape. Objects too heavy to be neutron stars collapse to black holes. Formation-
Formation Continued… As the mass increases, so does the gravitational pull. If the gravitational pull is such that even light can escape , then a black hole is formed.
Gravity deforms space time Diagrammatical representation
Event horizon The point at which no light can escape.
A nonrotating black hole has only a “center” and a “surface”. <ul><li>The black hole is surrounded by an event horizon which is the sphere from which light cannot escape </li></ul><ul><li>The distance between the black hole and its event horizon is the Schwarzschild radius (R Sch = 2GM/c 2 ) </li></ul><ul><li>The center of the black hole is a point of infinite density and zero volume, called a singularity </li></ul>
Falling into a black hole Falling into a black hole gravitational tidal forces pull spacetime in such a way that time becomes infinitely long (as viewed by distant observer). The falling observer sees ordinary free fall in a finite time.
Falling into a black hole <ul><li>Signals sent from the freely falling observer would be time dilated and red shifted. </li></ul><ul><li>Once inside the event horizon, no communication with the universe outside the event horizon is possible. </li></ul><ul><li>But incoming signals from external world can enter. </li></ul><ul><li>A black hole of mass M has exactly the same gravitational field as an ordinary mass M at large distances. </li></ul>
Rotating black holes <ul><li>A rotating black hole (one with angular momentum) has an ergo sphere around the outside of the event horizon </li></ul><ul><li>In the ergo sphere, space and time themselves are dragged along with the rotation of the black hole </li></ul>
1-Accertion disks and gas jets. 2-Strong Radiation emissions 3-Gravitational lensing Techniques for finding black holes
Types of Black Holes-- 1-Supermassive Black holes. 2-Stellar- mass black holes. 3-Intermediate mass black holes.
Advantages and Disadvantages-- They can be significant in this way: 1-Individual modes may dominate the time evolution of some perturbation, and a whole set of them could be used to completely describe this time evolution. The disadvantages are that – 1-when a black hole evaporates information is really gone. 2-Due to this there is trouble in energy conservation. 3-Invariance in time predictability.
References--- 1-www.google.com. 2-www.wikipedia.com. 3-Anatony on Black holes.