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Black Hole

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Introduction

Black Hole

Group No. 6

A black hole is a theorized celestial body whose surface gravity is so strong that no light can escape from within it. It is one of the three postulated final stages of stellar evolution wherein a star’s core cools and contracts and begins to collapse under the enormous weight of the outer layers. No black hole has ever been identified but scientists have described certain parts of the universe where they might exist.

A black hole is a theorized celestial body whose surface gravity is so strong that no light can escape from within it. Although black holes have been of intense scientific interest only in the later 20th century, the concept goes back to the French mathematician Pierre Simon de Laplace. In a 1798 treatise Laplace agreed with Isaac Newton that light is composed of particles. He reasoned that if enough mass were added to a star like the sun, the gravitational force of the star would eventually become so great that its escape velocity would equal the velocity of light.

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Middle

If a star more massive than the sun undergoes gravitational collapse at the end of its evolution, it will form either a white dwarf, a neutron star, or according to theory a black hole, depending primarily on its mass. If its collapse process is nonspherical, perhaps because the star is flattened at the poles, then theoretical gravitational waves could be given off just before the black hole is formed. Attempts are being made to detect such waves.

The only other way to identify a black hole would be through its interactions with other matter. For example, if the black hole is formed in a Binary Star System, gas from the normal star may later flow toward the black hole. As the gas falls toward the hole, its molecules increase in speed and approach the speed of light. The molecules begin to bunch up and collide, heating them to temperatures at which X-rays are emitted. Such X-rays have been detected in eclipsing binary star systems in which the X-ray source is not visible.

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Conclusion

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A popular misconception is that black holes act like cosmic vacuum cleaners, sucking up everything within reach. In fact the gravitational attraction of a black hole would be no stronger than that of a normal star of the same mass. For instance, if the sun could collapse to form a black hole (it cannot, however, and will instead end its life as a white dwarf), the earth would continue to orbit just as it does now.

Bibliography

“Black Hole.” The 1995 Grolier Multimedia Encyclopedia. USA: Grolier Electronic Publishing Inc., 1995.

“Black Hole.” Microsoft Encarta 97 Deluxe Edition. USA: Microsoft Corporation, 1996.

“Black Hole.” 1998 World Book Multimedia Encyclopedia. USA: World Book, Inc., 1997.

“Black Hole.” Compton’s New Century Encyclopedia and Reference Collection II. USA: Compton’s Learning Company, 1995.

Space Telescope Science Institute. “Hubble Provides Multiple Views of How to Feed a Black Hole” (PRC98-14). http://oposite.stsci.edu/pubinfo/pr/1998/14/.

Robert Nemiroff and Jerry Bonnell. National Aeronautics and Space Administration. “Astronomy Picture of the Day Index – Stars: Black Holes.” http://antwrp.gsfc.nasa.gov/apod/black_holes.html.

Steven Degennaro. The Search for Black Holes. http://www.owlnet.rice.edu/~spac250/steve/index.html.

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Response to the question

The candidates overall response is good, they have mentioned scientific theories, they have discussed contributions from important scientists and they have used images to help with their discussion which can be useful when talking about such a difficult concept. That ...

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Response to the question

The candidates overall response is good, they have mentioned scientific theories, they have discussed contributions from important scientists and they have used images to help with their discussion which can be useful when talking about such a difficult concept. That said, the candidates introduction is a little unclear and could be improved. When writing your introduction you need to state exactly what you are going to discuss within your essay, this is important as it makes the purpose of your essay clear. It can often be easier to add this into your introduction once you’ve finished as you will then know what you have discussed.

Level of analysis

It is clear that the candidate has taken the time to research this topic, which is always a good idea when writing a scientific essay. This enables you to include additional information within your essay which demonstrates a broader knowledge and can make your essay more interesting to read. Furthermore, the candidate has sensibly included a bibliography stating the resources they have used, this is important as it shows the reader the steps you have taken to prepare for your essay and it can show that your work is not plagiarised. That said, the candidate has unfortunately not written a conclusion for their work, this is a mistake, by not concluding your work you are unable able to leave the reader with a good impression. A good conclusion should summarise key points from your essay with reference to why these are important as these helps to tie together any loose ends.

Quality of writing

This essay is reasonably well written and the candidate has used appropriate technical terms throughout their work which demonstrates a good understanding of this topic. However there are one or two grammatical errors and some issues with spelling in which the candidate has used the American version of some words.


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