Black Holes & Related Phenomena, What Is a Black Hole Options

[kallubhai4u]

hi
this is what Visuja had asked 4 & i m delivering it now. hope it'll satisfy his needs.

If a ball is thrown upwards from the surface of the Earth it reaches a certain height and then falls back. The harder it is thrown, the higher it goes. Laplace calculated the height it would reach for a given initial speed. He found that the height increased faster than the speed, so that the height became very large for a not very great speed. At a speed of 40000 km/h (25000 mph, only 20 times faster than Concorde) the height becomes very great indeed - it tends to infinity, as the mathematician would say. This speed is called the `escape velocity' from the surface of the Earth, and is the speed which must be achieved if a space craft is to reach the Moon or any of the planets. Being a mathematician, Laplace solved the problem for all round bodies, not just the Earth.

He found a very simple formula for the escape velocity. This formula says that small but massive objects have large escape velocities. For example if the Earth could be squeezed and made four times smaller, the escape velocity would need to be twice as large. This surprisingly simple derivation gives exactly the same answer as is obtained from the full theory of relativity.

Light travels at just over 1000 million km/h (670 million mph), and in 1905 Albert Einstein proved in the Special Theory of Relativity that nothing can travel faster than light. The above Laplace formula can be turned around to tell us what radius an object must have if the escape velocity from its surface is to be the speed of light. This particular radius is called the `Schwarzschild radius' in honour of the German astronomer who first derived it from Einstein's theory of gravity (General Theory of Relativity). The formula tells us that the Schwarzschild radius for the Earth is less than a centimetre, compared with its actual radius of 6357 km.

the source of this info is a site mentioned below:-
http://csep10.phys.utk.edu/guidry/violence/black2.html

some more coming up soon.

[kallubhai4u]

hi, i've told 'bout Black Holes....& now i would tell u Where Might We Find Black Holes?. here is how it goes.

(source: http://csep10.phys.utk.edu/guidry/violence/black6.html )

It is impossible to observe a black hole directly and so any black hole candidates have to be identified by their effect on the matter surrounding them. If no other explanation for the observed phenomena is valid then it is likely that a black hole is present. There are some objects that are good candidates for the presence of a black hole.


Any star shines and survives because the pull of gravity, which is trying to compress it, just balances the pressure generated by the nuclear furnace at its centre, which is trying to expand it. Once the furnace runs out of fuel, which must eventually happen, the pressure decreases, loses its battle with gravity, and the star collapses. Astronomers believe that one of only three things can happen to a star in this situation, depending on its mass. A star less massive than the Sun collapses until it forms a `white dwarf', with a radius of only a few thousand kilometers. If the star has between one and four times the mass of the Sun, it can produce a `neutron star', with a radius of just a few kilometers, and such a star might be recognised as a `pulsar'. The relatively few stars with greater than four times the mass of the Sun cannot avoid collapsing within their Schwarzschild radii and becoming black holes. So, black holes may be the corpses of massive stars.

Most astronomers believe that galaxies like the Milky Way were formed from a large cloud of gas which collapsed and broke up into individual stars. We now see the stars packed together most tightly in the centre, or nucleus. It is possible that at the very centre there was too much matter to form an ordinary star, or that the stars which did form were so close to each other that they coalesced to form a black hole. It is therefore argued that really massive black holes, equivalent to a hundred million stars like the Sun, could exist at the centre of some galaxies.