The Life Cycle
Running head: THE LIFE CYCLE OF THE STARS
The Life Cycle of the Stars
September 03, 2007
The Life Cycle of the Stars
Stars come in many definitions and in many forms today, there are Rock Stars, Movie Stars, There is even star shaped cereal for children but the most important stars we have our in our solar system. Let us look at the stars in the sky and space, their origins of birth, their features of life, and their features in death.
Light is an important part of a stars life, because light is what a star emits and makes it visible to us. Through the study of starlight, the discovery the Earth orbits the sun appeared. In addition, the aberrations of starlight eventually lead to the discovery of stellar parallax in 1838. There are many forms of photons and electromagnetic waves and because of the various forms and shapes, we are able to study star by the light that they emit.
In the Hierarchy of the universe, stars play an important role. They are huge bodies that have come into being from great clouds of light elements, either with the stars forming simultaneously, or in later evolution of the galaxies. When a star is born out of enormous clouds of gas and dust, they come together into a gigantic ball. Then there is the pressure from all the gas and dust banging into each other and it can reach millions of degrees in temperature. The from this temperature come a life spawn out of an environment of nuclear fashion and it omits light and thus a star is born. The way that a star and our sun produce light is through the process of nuclear fusion. Einstein’s theory of relativity, E-mc squared, has proven this. The makeup and chemical composition is very closely the same from star to star. There are differences in a star’s mass, and through what phase of their life they are passing.
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There are three main groups of stars. Low mass stars, they are born with less than two times the mass of our sun. Intermediate stars, which are about 8 time the size and mass of our sun. Finally, there are high mass stars that are larger than 8 times the size ad solar mass of our sun. The formation of a star starts from a cloud of matter that forms a proto-stellar disk, similar to the way our solar system developed. The proto-star is much like a star but its central temperature is not quite hot enough for fusion. Once the temperature rises inside the photo star by gravitational contraction, the temperature rises and the energy flows to the surface. When the core temperature reaches 10 million degrees Kelvin, it is hot enough to become a full-fledged star.
Now the star has become a fusion furnace of sorts, it steadily burns hydrogen. The size and birth weights all vary and are of different mass. There is a ten to one ratio in favor of forming low mass and intermediate mass stars over high mass stars. The Low mass stars spend there main life as a fusion machine which turns hydrogen into helium and a slow and methodical pace. When the energy released by this fusion reaches the surface, and released into space, this is the star luminosity. Over a long, longtime, sometimes billions of years, a low mass star consumes the hydrogen in its core and converts it to helium, at which point the core starts to contract and shrink. Once all the hydrogen inside the stars core begins to become fully exhausted, the core pressure gives way to the crush of gravity because it has no more fusion occurring in its core then. As the core shrinks rapidly and the outer layers start to expand, the star’s shape begins to grow in size. Its luminosity becomes extraordinarily bright, because of the outer shell starting to produce fusion more rapidly then the core. As this grows more extreme, the core starts to burn rapidly again and fuse its core helium into carbon. Then just before its final death, the star ejects its outer layers into space. This leaves only the degenerated carbon core. This core is still very hot and it emits intensely powerful ultraviolet radiation and glows brightly. This is a planetary nebula. The nebula fades and cools over a million or so years, and we then have a white dwarf. The white dwarf cools until it is not viewable any more and will then become a black dwarf.
High mass stars are the producers of all the elements that life itself depends on. In the early stage of a high mass stars existence to is much like that of a low mass star. The difference between the two is in there final life stages. Unlike the low mass star, when a high mass star has finished its fusion process it explodes into a cataclysmic event known as supernova. In its life sequence, the hydrogen core of a high mass star reaches a much higher temperature than a low mass star. The rate of fusion increases because of these higher temperatures and make it possible to go through a CNO cycle or carbon, nitrogen and oxygen cycle. This CNO Cycle creates massive amount of power and speeds up the hydrogen fusion process. The hydrogen in the core of the high mass star exhausts much faster and causes the star to fuse helium into carbon much faster. Since the carbon core shrinks, the crush of gravity intensifies and the density, pressure and temperature rise causing helium burning shell to form the inert burning core and the hydrogen shell and the outer layers begin to swell again. The high mass stars core keeps exhausting the elements it is fusing and keeps heating up and becoming hot enough for other fusion reactions. Once the high mass star develops further, through fusing the elements essential for life, it gains an iron core, which cannot release energy by fusion or fission. Therefore, the core keeps growing the only way it can resist the crush of gravity is to explode in a titanic explosion known as a supernova, and the ball of neutrons left after this is a neutron star.
So there we have it, the life cycle of stars may differ in the size, mass and death but they all go through a birth, life-and-death cycle much as we ourselves do. We as humans sometimes live like stars, some of us have a brighter and more massive impact then others, and some of us go out in a blaze, like a supernova.
Bennett , R., Donahue, G., Schneider, J., & Voit, N. (2004). The Cosmic Perspectives (3rd ed ed.). NY: Pearson Addison Wesley.
Kosmoi (1999). Electromagnetic Radiation. Retrieved August 29 2007, from http://kosmoi.com/Science/Physics/Light/
Merriam Webster Online (2005). Star. Retrieved Aug 25 2007, from http://www.m-w.com/dictionary/star
MilkyWay.Com (2005). Evolution of Stars. Retrieved August 15 2007, from http://www.milky-way.com/gb/sevol.htm
Here's what a star student thought of this essay
Quality of writing
Quality of writing - Is the writing accurate in terms of spelling, grammar and punctuation? Has the writer used technical terms expected at this level of qualification? To what extent does the writer follow conventions and expectations for written work at this level? Grammar and spelling was good. However, the only thing that the writer could have avoided is trying to be trivial in the introduction and ending paragraph by talking about "Rock Stars" and "Film Stars".
Level of analysis
Level of analysis - To what extent does the writer show appropriate analytical skills for this level of qualification? Have they made evaluative judgements using suitable evidence? Have these examples been developed throughout the response and has an appropriate conclusion been reached? The language that the writer used within their essay was of a high standard. They used the correct scientific language, especially when naming each stage of the life cycle correctly and explain the significance of each stage. The information is mainly accurate, although again the main point that they could have analysed more was the point on nuclear reactions, mainly because it plays a massive part in the life cycle of stars.
Response to question
Response to question - To what extent has the student answered the set question? How explicit is their response? The writer has approached the question well, where they used information that could potentially be very complex and broken it down for people to understand, without loosing any essential facts. It was good that they went through a very quick history before actually discussing the life cycle of stars. They mention nuclear fusion and Einstein's theory of relativity, but hasn't been able to link both star cycles and this very well together. What the writer could have done is briefly explain this process. It was good that the writer explained the differences between star masses and the relation to out sun. It was also good that the writer explained the similarities and differences that the life cycle of the star would have depending on its' mass and what happens to each star group as it comes towards the end of it's life and finally dies. Overall, it was a good response and a very well written essay.