Black Hole Essay Research Paper Black holeAn

Black Hole Essay, Research Paper

Black hole

An image of the core of the Whirlpool galaxy M51 taken by the Wide Field Planetary Camera onboard the Hubble Space Telescope. It shows an immense ring of dust and gas which is thought to surround and hide a giant black hole, 1 million times the mass of the Sun, in the center of the galaxy. The ring forms an accretion disc of gas, about 100 light years across, falling toward the black hole. The two brighter areas perpendicular to the widest dark lane are two jets of particles accelerated by the black hole.

Anyone who has ever watched the launch of a rocket is familiar with the concept that escape from a gravitational field requires the expenditure of energy. The stronger the gravitational field, more energy is required to escape from its clutches. If the rocket has insufficient fuel, it will return to Earth and escape is impossible. Thus, it is not hard to imagine a gravitational field strong enough to prevent the escape of any object with a finite amount of energy.

The gravitational force of an object is governed by a combination of the amount of matter it contains and its volume. The more the matter is confined in progressively smaller volume, the larger the gravitational field at the surface of the object. Since even a light beam has a finite amount of energy, one can imagine a massive object in a sufficiently small volume that would posses a gravitational field strong enough to prevent the escape of that light. The French mathematician Simon Laplace reasoned in 1795 that, if Newton’s corpuscular theory of light were correct, there could exist massive object from which light could not escape.

Indeed, any theory of gravity should contain the notion of such an object. In the case of Einstein’s theory of General Relativity, we call such an object a black hole.

However, in the case of general relativity, the path taken by a light beam defines the geometry of space-time for it represents the “shortest distance between two points.” Such a path is called a geodistic . Thus, for a black hole in general relativity, a light beam originating on the surface that cannot escape really travels nowhere. In some sense, all “surface” points can be viewed as the same point and the object can be said to have been sealed off from the ordinary space and time of outside observers. The point from which light can no longer escape is known as the event horizon since knowledge of events beyond that point can never be transmitted to the outside world by a light beam or any other mechanism. The event horizon imposes a form of censorship on the makeup of a black hole. Indeed, the only aspects of a black hole that may be ascertained from outside are its mass, net charge, and rate of spin. No internal processes that depend on time in any way can be detected in the external environment, for that would constitute sending signals from inside the black hole to the outside when not even light can escape. This “censorship” is what is responsible for the small number of measurable properties of the black hole itself-mass, spin, and charge.

While there are complications in defining the size of a black hole, one can uniquely specify its circumference and thus define a radius as just the circumference divided by 2. This radius is known as the Schwarzschild radius after Karl Schwarzschild, who first defined it as R s=2GM/c 2. Here M is the mass of the black hole, G is the Newtonian constant of gravity, and c is the speed of light. However, R s should not be viewed as the distance from the event horizon of the black hole to its center. The geometry of space-time in the interior of the black hole is so warped that Euclidean notions of distance no longer apply. Nevertheless, R s does provide a measure of the space around a particular mass M that will be seriously warped. R s for an object having the mass of the sun is about 3 km. Thus, to turn the Sun into a black hole, one would have to cram all of its mass into a sphere having about a 3 km radius. Squeezing any such mass into a volume dictated by its Schwarzschild radius posses a serious assembly problem. In fact, about the only processes which might lead to the formation of a black hole involve the death of moderately massive normal stars or the formation of supermassive stars.

As evolving stars exhaust the nuclear fuel which enables them to support their own weight and shine at the same time, they begin a rapid collapse. It is believed that the crushing self-gravity of the collapsing star may be sufficient to form a black hole with the mass of several times that of the Sun. Such black holes would have Schwarzschild radii of several to perhaps a few tens of kilometers. Considering their mass, they are really tiny things. If one were to replace the Sun with a black hole of the same mass as the Sun, there would be a region of space a few kilometers in size located where the center of the Sun currently resides where space would be extremely warped. However, the gravitational field of this object, measured at the distance of the Earth, would be exactly that of the present-day Sun. The Earth and planets would continue in their orbits and except for it being rather dark, the solar system would continue much as it does today. If one were to launch a rocket from the Earth to hit the black hole, the task would be immensely more difficult than hitting the Sun. The Sun pres