Pierce CP English 2 20 April 2000 Black Holes A Black hole is a theorized celestial body whose surface gravity is so strong that nothing, including light, can escape from within it's surface. Gravity is the key to a black hole's immense power. The black hole's strong gravity keeps captured material from escaping. For example, if Earth were the same mass it is now but had only one-fourth its present radius, the escape velocity of someone standing on its surface would be twice what it is now.Black holes have a power far greater than our minds can imagine. This report will go into further discussion on these massive holes in space.
Now, though, astronomers have uncovered a much better candidate for a black hole in our galaxy. It lies in the constellation Monoceros some three or four thousand light-years away. Monoceros was discovered in 1975, when it emitted a shower of light and x-rays.Observations soon revealed that Monoceros was a binary consisting of an orange dwarf star and a dark companion. Astronomers continue to observe the object and other black holes like it.
Despite its name, A0620-00, it is a better candidate for a black hole than Cygnus X-1.(Croswell 30-37) Peters 2 As I said before, gravity is the key for a black hole's immense power. The black holes strong gravity keeps captured material from escaping. Of course, every moon, planet, and star has gravity. Earth has enough gravity that you have to travel faster than 11 kilometers per second to overcome the force of gravity.This number is Earth's escape velocity.
The gravity of Jupiter is even stronger: it's escape velocity is 60 kilometers per second. A black hole has so much gravity that to escape one you would have to be traveling faster than the speed of light, 300,000 kilometers per second. But traveling faster than the speed of light is impossible, so once you get into a black hole you can't get out.(Levitt 83) Black holes may form during the course of stellar evolution. As nuclear fuels are exhausted in the core of a star, the pressure associated with their heat is no longer available to resist contraction of the core to ever higher densities.
Two new types of pressure arise at densities a million and a million billion times that of water, respectively, and a compact white dwarf or a neutron star may form. If the core mass exceeds about 1.7 solar masses, however, neither electron nor neuron pressure is sufficient to prevent collapse to a black hole. Knowing more about galactic black holes will help astronomers learn more about the evolution of galaxies and the relationship between galaxies, black holes, and quasars. Astronomers Holland Ford, Richard Harms, and colleagues have used data from the Hubble Space Telescope to develop strong evidence that a black hole exists in the center of the elliptical galaxy M87 in Virgo.
Ford and Harms have shown that a small mass, fast rotating disc lies at M87's heart.(Powell 12) There is also a black hole Peters 3 that is eating the Milky Way.The core of the Milky Way galaxy, 180 quadrillion miles from Earth, exerts enough force to hold together a system of 100 billion stars. Astronomers trying to determine the origin of this force think they may have found the answer-a black hole at the center of the galaxy with the mass of three million suns, sucking in matter and emitting odd radio waves and other signals.
Astronomers first noticed a glow of gamma radiation at the center of the galaxy in the 1970's. But the most convincing evidence was a motionless source of radio waves that were detected at the center of galaxy. All of these factors indicate a supermassive center that is absorbing matter into it's gravitational field at great speed.(Sawyer 38) Using a series of radiotelescopes stretching 5,000 miles across the United States from the Virgin Islands to Hawaii, an international team of astronomers have discovered strong evidence of an incredibly powerful black hole as massive as 40 million suns. The findings, presented to the American Astronomical Society in Tucson Wednesday and published today in the journal "Nature," is considered the strongest evidence yet of the existence of black holes.
It is difficult to prove the existence of black holes primarily because, by definition, they can never be seen. At best, scientists can only study the that would be expected in the surrounding territory if in fact a black hole is there. By several accounts, astronomers projects from the 1980's have come closer than any of the others. Scientists lust after evidence of black holes because they are among the most mysterious objects in the universe, devouring everything within their gravitational reach. Their immense pull is believed responsible for swirling masses of stars that radiate brilliantly across the heavens.
A fuller understanding of black holes is considered Peters 4 essential to comprehending the physics that drives celestial objects from quasars to galaxies.(Dye A3+) Abraham Loeb believes that black holes fueling active galactic nuclei form when protons left over from the creation of the universe interact with electrons or dust in gas clouds to create a drag force. The force slows the clouds rotation enough to allow extreme gravitational collapse.(Cowen 86) Scientists believe that a black hole forms when a very massive star runs out of nuclear fuel and is crushed by its own gravitational force. While a star burns fuel, it produces an outward push that counters the inward pull of gravity.
When no more fuel remains, the internal pressure drops, and the star can no longer support its enormous weight. It throws off its outer layers in a gigantic explosion.At the same time, it's core collapses. Gravity can crush a core measuring 10,000 miles (16,000 kilometers) across to an object 10 miles (16 kilometers) across in about one second. Very few stars become black holes when they die. Most massive stars collapse to become neutron stars (dense stars made up almost entirely of neutrons).
Scientists are sure that neutron stars form by collapse. They suspect that a black hole will form in the same way if a star's burned out core contains at least three times the mass of the sun. The idea of a black hole is based on physicist Albert Einstein's theory of gravitation, known as general relativity. Einstein's theory predicts that a black hole formed by the collapse of a star about 100,000 times smaller than the sun and almost featureless.Therefore, it would make it extremely difficult to pinpoint a black hole.(World Book)*** Astronomers believed that black holes could only be an intermediate step toward Peters 5 the completion of spherical gravitational collapse or a disappearance in what the astronomers call a "singularity." The singularity is a region of space-time where infinitely intense gravitational forces deform matter and photons beyond recognition and, as the radius of a sphere shrinks to a point of zero dimension and the volume goes to zero, matter and energy are squeezed out of exi ...
