What are stars made of?

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Katy Morris        Page         5/2/2007






What are stars made of?

How do we know?

Contents Page

The Life Cycle Of A Star.        

Information Used From the following Websites:

Books Used:

Stars and Supernovas – Iain Nicholson

Stars and Planets –Ian RidPath

What Are Stars Made Of?

Stars are made of very hot gasses, mainly hydrogen and helium.  The gas gets denser and hotter as you had toward the middle of the star.

        In the sun the temperature reaches 15 million degrees Celsius.  The largest stars make other elements in their cores, as a by-product of the nuclear fusion that powers them.  Most material in the earth and in our bodies has been created in this way in the stars and spread throughout the galaxy by supernova explosions.  So basically, stars are big exploding balls of gas, mostly hydrogen and helium.


The Life Of A Star.

Our nearest star, the Sun, is so hot that the huge amount of hydrogen is undergoing a regular star-wide nuclear reaction, like in a hydrogen bomb. Even though it is frequently exploding in a nuclear reaction, the Sun and other stars are so large and have so much matter in them that it will take billions of years for the explosion to use all the "fuel" in the star. The huge reactions taking place in stars are frequently releasing energy (called electromagnetic radiation) into the universe, which is why we can see them and find them on radio telescopes such as the ones in the Deep Space Network (DSN). Stars, including the Sun, also send out a solar wind and burst out occasional solar flares.

Hubble Space Telescope Image from the Astronomy Picture of the Day Archive. http://antwrp.gsfc.nasa.gov/apod/ap990113.html

The Sagittarius Star Cloud, found at the centre of our galaxy. The colour of the star is linked to temperature that it is. A relatively cool star would be yellow like our Sun would seem dim in this photograph.

The Life Cycle Of A Star.

Stars are born from clusters of interstellar matter

Outer space is not an absolute vacuum. In fact, it is filled with very thin clouds of hydrogen and helium, and dust-like interstellar particles. These are the raw materials of future stars. Clusters of interstellar particles attract more and more other particles, gradually increasing in size. Eventually, the cluster begins to contract by virtue of its own gravity. Then, when the core temperature has reached around 10 million degrees, a nuclear reaction begins. The period up until this point is known as the "contraction phase" and, in the case of a star with a mass similar to that of our Sun, takes about 500 million years.

The longest period in a star's life is as a main sequence star

Once the contraction phase is completed, the star becomes a fixed star, an "adult" so to speak, and enters the main sequence star phase. Stars in this phase produce energy as the result of a nuclear reaction that creates one helium atom from every four hydrogen atoms. This means that the amount of hydrogen in the star gradually decreases, while the helium increases. The main sequence star phase is the longest period in a star's life, and in the case of a star with a mass similar to that of our Sun, lasts for about 10 billion years. Our Sun is thought to be around 4.6 billion years old, which means that it is probably about halfway through its main sequence star phase.

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As the outer layers expand from the helium core, the star becomes a red giant

The helium at the centre of the star continues to increase until a helium core is formed. A Nuclear reaction then begins to spread outward. As the helium core grows heavier, the core's temperature also increases, and the outer layers begin to expand until the star becomes a massive red star known as a red giant.

In the case of a star that is about the size of our Sun, the gases of the outer layer are ...

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