Life of a Massive Star

     What kind of massive stars are we talking about? Main sequence stars that have 10-30 solar masses will be discussed.

     In the wanderings of space, the particle density is so many times lower than the density of air that in Earth it would be described as a perfect vacuum. It is important to know that vacuum in space has a density and the density is not zero. The "material" that makes up the vacuum is called the interstellar medium. It mainly consists of hydrogen and helium. How much of space is actually not a vacuum? A very tiny amount. Since hydrogen and helium make up the vacuum, they are by far the most abundant elements in the Universe.

     As the density of the interstellar medium increases due to condensation, we now have an interstellar cloud. It is still has very low density. Particles attract each other due to gravitational force and hold the cloud together.

Over time, if the interstellar cloud is large enough, it will contract and particles will move at higher speeds (temperature rises). This process continues until the temperature is high enough that the atoms collide violently and stripped off of their electrons. Two gases emerge: nuclei gas composed of hydrogen nuclei (protons) and a gas of free electrons. The gases repel each other and they are stable. This is called plasma.

Since every star dies after a long period of time, it follows the steps of evolution. Here are the steps of evolution from the birth of the star to its death.

Stage 3 of the evolution process is called the pro-star.  At this stage the star begins to glow and emit its own light because the compression of the cloud generates heat which gives cloud its own light. At this point the surface and radiation of the star is incredible due to its huge size.

At stage 4, the two nuclei of the proto-star collide together because the temperature becomes so great, reaching 15000000 K, that it causes them to merge together. After they unite the nuclear furnance will continue to burn until the star dies. At this stage the proto-star can now be called a young star.

During stage 5 a star matures and continues to burn. Most of its hydrogen converts into helium through the process called nuclear fusion. At this stage the star reaches equilibrium and depending on the surface temperature will radiate a white/yellow light. As we know the higher the temperature, the bluer the star will be & the lower the temperature the redder it will be.

Stage 6 is called the red giants. The star's brightness will increase by nearly half as much, while the hydrogen supply will only decrease. The temperature of the outside of the core will reach around 15000000 Kelvin which will make it expand. As an example, when our sun will become a red giant it will reach Venus in size and the Earth will be burned to ashes!

At stages 7 & 8 the temperature of the core of the star will rise reaching 100000000 K. When the inside of the core becomes even hotter, that way increasing the pressure, it will cause an even faster nuclear reaction- adding more heat to the core of the star. When the pressure becomes too great the star explodes. The core of the star will expand through helium explosion which will cool off the hot star. Then the star will expand into a red giant once more- a process which can only take a few million years!

During stage 9, last stage, the star dies. Unlike the medium size stars, large stars will not have a massive nuclear reaction simply because the core is less dense. The star will cool and shrink once the oxygen and carbon are gone, which yet again will heat the core and once it reaches trillions of degrees, explosion such as Supernova will occur. Since it is a large star, the explosion will significantly be brighter, shattering the atomic nuclei to pieces.

In 2006, astronomers were excited about star formation in Arp 220, a super galaxy created by the collision of two other galaxies 250 million light-years from Earth. The Hubble Space Telescope has observed more than 200 huge star clusters, giving scientists a glimpse of what occurred when the universe was young. A surprising find was that the mix of gas and dust in this new galaxy is very similar to our own older Milky Way.

Bibliography

1. http://www.milky-way.com/gb/sevol.htm
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3. http://www.cartage.org.lb/en/themes/sciences/Astronomy/Thestars/evolutionstars/evolutionstars.html
4. http://hven.swarthmore.edu/~cohen/winds/wind_bubble.jpg
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