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The aim of this report is to give a clear summary of the main points surrounding the often confusing topic of black holes.

Extracts from this document...

Introduction

Philip Jenkins

Physics Coursework - Research and Report

BLACK HOLES


The aim of this report is to give a clear summary of the main points surrounding the often confusing topic of black holes. Many people are fascinated by these phenomena, but how many could say for sure what a black hole is?

So to start, I feel that a proper definition of a black hole is needed.

A black hole is an object from which nothing can escape, or to put more accurately, a black hole is an object small enough that
its escape speed exceeds the speed of light.

“Escape speed?”
You may ask, but more on this later. The first part of the report will concentrate on the history of the black hole theory and how it has developed over time.

History Lesson

The name “black hole” was created in 1967, but the idea is not so modern as the beginnings of the theory can be traced back to the eighteenth century. The theory of the black hole can be linked to the theory of light, which culminated in Einstein’s General Theory of relativity in the early twentieth century. This theory married space and time, and could only be achieved thanks to the relative weakness of gravity as a force. As you approach a black hole, gravity becomes much stronger, so it dominates over any other force distorting the common rules of space and time, causing weird and wonderful phenomena which one cannot imagine or relate with.

Einstein’s theory can be adapted to black holes (see later), but before his era, the notion of black holes had been toyed with.

...read more.

Middle




Detecting Black Holes

Black holes are invisible, so you may think that it is impossible to detect their presence if you can’t see them. This is not the case however, as by measuring the effects a black hole’s gravity has on its surrounding space (and any objects therein) is fairly simple, and there are several characteristics which are thought to be unique to black holes.

1. Mass
Due to its huge mass, a black hole causes strange things to occur around it. If a black hole is near another star, then the star’s matter is pulled towards the black hole. The black hole is said to accrete matter into itself - which forms an Accretion Disc around the circumference of the black hole

image13.jpg

Picture courtesy NASA

By observing what occurs to objects around a black hole (factors such as rotation speed) the mass of the black hole can be estimated using Keplar’s Third Law. The picture below shows the core of a galaxy called NGC 4261. The brown disc at the centre is the same size as our solar system, but the body which it is orbiting around weighs 1.2 billion times as much as the Sun. For this mass to be compressed into such a relatively small space the most feasible explanation is a black hole.

image14.jpg
Photo courtesy NASA/Space Telescope Science Institute
Credit: L. Ferrarese (Johns Hopkins University) and NASA

2. Discharge of X-Rays and Jets

When matter has been drawn into a black hole’s accretion disc, the gravitational force accelerates the material to immense speed, causing it to heat up to millions of degrees Kelvin. This superheated

...read more.

Conclusion


"The universe is not only stranger than we imagine, but stranger than we can imagine."

J.B.S Haldane













Bibliography

“A brief history of black holes” Richard Buckley (2000) From “Physics Review” pp 18-20

A useful source, containing the mathematics behind black holes and a concise history of their discovery.

“The identification of Cygnus X-1 as a black hole” Steve Degennero (1996)
http://www.owlnet.rice.edu/~spac250/steve

Fantastic case study of Cygnus X-1, however needed some careful reading due to the fact that this included university level physics.

“The look of a black hole”
http://www.leyada.jlm.k12.il/proj/black/look.htm

A smaller web site, with no obvious author, so reliability not the greatest.

“How Black Holes Work” Craig C. Freudenlich, Ph.D. (2001)
http://www.howstuffworks.com/black-hole.htm

The best source on black holes which I found. Many of the pictures in this report are from this site. Also included many useful links for black hole resources.


“Imagine the Universe - Black Holes”
http://imagine.gsfc.nasa.gov
Imagine the Universe is a service of the High Energy Astrophysics Science Archive Research Center (HEASARC), Dr. Nicholas White (Director), within the Laboratory for High Energy Astrophysics at NASA's Goddard Space Flight Center.

The Imagine Team
Project Leader: Dr. Jim Lochner
Curator:Meredith Bene Ihnat
Responsible NASA Official:Eunice Eng

A good Advanced Level site, with another case study on the black hole Cygnus X-1. NASA backing makes this one of the most reliable sources.


...read more.

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