... with the proper equipment, can be detected and seen as an image of a black hole. Through this technique, astronomers now believe that they have found a black hole known as Centaurus A. The existence of a star apparently absorbing nothingness led astronomers to suggest and confirm the existence of another black hole, Cygnus X 1.
By emitting gravitational waves, non-stationary black holes lose energy, eventually becoming stationary and ceasing to radiate in this manner. In other words, they decay and become stationary black holes, namely holes that are perfectly spherical or whose rotation is perfectly uniform. According to Einstein's Theory of General Relativity, such objects cannot emit gravitational waves. Black hole electrodynamics is the theory of electrodynamics outside a black hole. This can be very trivial if you consider just a black hole described by the three usual parameters: mass, electric charge, and angular momentum. Initially simplifying the case by disregarding rotation, we simply get the well known solution of a point charge.
This is not very physically interesting, since it seems highly unlikely that any black hole (or any celestial body) should not be rotating. Adding rotation, it seems that charge is present. A rotating, charged black hole creates a magnetic field around the hole because the inertial frame is dragged around the hole. Far from the black hole, at infinity, the black hole electric field is that of a point charge. However, black holes do not even have charges.
The magnitude of the gravitational pull repels even charges from the hole, and different charges would neutralize the charge of the hole. The domain of a black hole can be separated into three regions, the first being the rotating black hole and the area near it, the accretion disk (a region of force-free fields), and an acceleration region outside the plasma. Disk accretion can occur onto super massive black holes at the center of galaxies and in binary systems between a black hole (not) and a super massive star. The accretion disk of a rotating black hole, is, by the black hole, driven into the equatorial plane of the rotation. The force on the disk is gravitational. Black holes are not really black, because they can radiate matter and energy.
As they do this, they slowly lose mass, and thus are said to evaporate. Black holes, it turns out, follow the basic laws of thermo-dynamics. The gravitational acceleration at the event horizon corresponds to the temperature term in thermo-dynamical equations, mass corresponds to energy, and the rotational energy of a spinning black hole is similar to the work term for ordinary matter, such as gas. Black holes have a finite temperature; this temperature is inversely proportional to the mass of the hole.
Hence smaller holes are hotter. The surface area of the event horizon also has significance because it is related to the entropy of the hole. Entropy, for a black hole, can be said to be the logarithm of the number of ways it could have been made. The logarithm of the number of microscopic arrangements that could give rise to the observed macroscopic state is just the standard definition of entropy. The enormous entropy of a black hole results from the lost information concerning the structural and chemical properties before it collapsed. Only three properties can remain to be observed in the black hole: mass, spin, and charge.
Physicist Stephen Hawking realized that because a black hole has a finite entropy and temperature, in can be in thermal equilibrium with its surroundings, and therefore must be able to radiate. Hawking radiation, as its known, is allowed by a quantum mechanism called virtual particles. As a consequence of the uncertainty principle, and the equivalence of matter and energy, a particle and its antiparticle can appear spontaneously, exist for avery short time, and then turn back into energy. This is happening all the time, all over the universe. It has been observed in the "Lamb shift" of the spectrum of the hydrogen atom. The spectrum of light is altered slightly because the tiny electric fields of these virtual pairs cause the atom's electron to shake in its orbit.
Now, if a virtual pair appears near a black hole, one particle might become caught up in a the hole's gravity and dragged in, leaving the other without its partner. Unable to annihilate and turn back into energy, the lone particle must become real, and can now escape the black hole. Therefore, mass and energy are lost; they must come from someplace, and the only source is the black hole itself. So the hole loses mass. If the hole has a small mass, it will have a small radius. This makes it easier for the virtual particles to split up and one to escape from the gravitational pull, since they can only separate by about a wavelength.
Therefore, hotter black holes (which are less massive) evaporate much more quickly than larger ones. The evaporation timescale can be derived by using the expression for temperature, which is inversely proportional to mass, the expression for area, which is proportional to mass squared, and the blackbody power law. The result is that the time required for the black hole to totally evaporate is proportional to the original mass cubed. As expected, smaller black holes evaporate more quickly than more massive ones.
The lifetime for a black hole with twice the mass of the sun should be about 10^67 years, but if it were possible for black holes to exist with masses on the order of a mountain, these would be furiously evaporating today. Although only stars around the mass of two suns or greater can form black holes in the present universe, it is conceivable that in the extremely hot and dense very early universe, small lumps of over dense matter collapsed to form tiny primordial black holes. These would have shrunk to an even smaller size today and would be radiating intensely. Evaporating black holes will finally be reduced to a mass where they explode, converting the rest of the matter to energy instantly. Although there is no real evidence for the existence of primordial black holes, there may still be some of them, evaporating at this very moment. The first scientists to really take an in depth look at black holes and the collapsing of stars, were professor Robert Oppenheimer and his student, Hartland Snyder, in the early nineteen hundreds.
They concluded on the basis of Einstein's theory of relativity that if the speed of light was the utmost speed of any object, then nothing could escape a black hole once in its gravitational orbit. The name 'black hole' was given due to the fact that light could not escape from the gravitational pull from the core, thus making the "black hole " impossible for humans to see without using technological advancements for measuring such things as radiation. The second part of the word was given the name 'hole' due to the fact that the actual hole is where everything is absorbed and where the central core, known as the singularity, presides. This core is the main part of the black hole where the mass is concentrated and appears purely black on all readings, even through the use of radiation detection devices. Just recently a major discovery was found with the help of a device known as The Hubble Telescope. This telescope has just recently found what many astronomers believe to be a black hole, after focusing on a star orbiting empty space.
Several pictures were sent back to Earth from the telescope showing many computer enhanced pictures of various radiation fluctuations and other diverse types of readings that could be read from the area in which the black hole is suspected to be in. Several diagrams were made showing how astronomers believe that if somehow you were to survive through the center of the black hole that there would be enough gravitational force to possible warp you to another end in the universe or possibly to another universe. The creative ideas that can be hypothesized from this discovery are endless. Although our universe is filled with many unexplained, glorious phenomena, it is our duty to continue exploring them and to continue learning, but in the process we must not take any of it for granted. As you have read, black holes are a major topic within our universe and they contain so much curiosity that they could possibly hold unlimited uses. Black holes are a sensation that astronomers are still very puzzled with.
It seems that as we get closer to solving their existence and functions, we only end up with more and more questions. Although these questions just lead us into more and more unanswered problems we seek and find refuge into them, dreaming that maybe one far off distant day, we will understand all the conceptions and we will be able to use the universe to our advantage and go where only our dreams could take us. Bibliography 1. ) Parker, Barry. Colliding Galaxies. 2.
) Hawking, Stephen. Black Holes and Baby Universes. 3. ) Encyclopedia Brittania.
Volume II, Black Holes. (c) 1996.