SCIENTIFIC BACKGROUND
What is a Star?
A star is a ball of gas, held together by gravity that gives off heat and light (Dejoie and Truelove, n.d.). The gasses involved are mainly Hydrogen, around 75%, and Helium, around 25%, with just a small percent left over consisting of a mix of elements. The exact percentages and elements in each star vary, as it is depends on what elements are available when the star is born. The amount available will also determine how big the star will become which in turn affects the path it takes during its life cycle.
How is a Star Born?
A star is born in a cloud of gas and dust called a nebula (Knight, 1997). Initially the cloud is cool but as gravity pushes in on it and the particles inside begin to collide the temperature begins to rise. Gravity continues to push until in the middle, a protostar forms (Knight, 1997). The protostar continues to gain mass as gravity continues to push in and heat up until conditions are right to sustain nuclear reactions and this is when a star is born (Scientific, n.d.).
Nuclear Fusion
Once a star is born it continually goes through nuclear fusion converting lighter elements, hydrogen, into heavier elements, helium (Scientific, n.d.). Fusion takes two hydrogen atoms, consisting of one proton each, and fuses them together to form helium atoms, that consist of two protons, see figure #1 (Knight, 1997). Gravity continues to push on the star, trying to compact it further, but the nuclear fusion pushes back allowing the star to continue to exist. This state where the gravity pushing in balances the radiation pushing out happens while the star is in the main sequence stage (Scientific, n.d.). This balance called hydrostatic equilibrium keeps the star from collapsing or blowing up, see figure #2 (Pogge, 2006). See “life cycle” for more about the main sequence stage.
Figure #1
(Periodic, 1997)
Figure#2
(Pogge, 2006)
Life Cycle
After a star is born from a stellar nebula it can take one of two paths depending on its mass, these being an average star or massive star. Average stars have a longer life cycle as they burn their fuel slower than more massive stars (Knight, 1997). Since they have a smaller mass they don’t experience as much gravity therefore, they don’t have to produce as much gas pressure to push back to create an equilibrium (Pogge, 2006). During this stage of equilibrium the stars wither, average or massive, this is considered part of the main sequence. This equilibrium becomes compromised, as nuclear fusion slows down from lack of hydrogen present. Both average and massive stars at this stage begin to fuse helium causing the star to collapse leaving a hot core with an outer surface that begins to expand and cool (Knight, 1997). The stars can expand to be 100 times larger than the original stars surface area (Knight, 1997). Average stars become red giants, red indicating a cooler temperature and giant indicating that it has expanded. Massive stars become red supergiants an example would be Betelgeuse located in the constellation Orion. Eventually, the outer surface becomes separated and at this point is considered a planetary nebula. A planetary nebula has nothing to do with a planet it can; however, it can be mistaken to look like one. The small, white, and initially hot core, known as a white dwarf, is left to cool until it turns into a black dwarf where no more light is given off (Scientific, n.d.). A red supergiant similarly begins to run out of hydrogen but when it collapses it is in the form of an explosion referred to as a supernova. The remnants of the explosion can leave behind a neutron star or a black hole. As one would imagine with an explosion, matter gets spread out everywhere. But in this case there is also a small core left behind that is so compact the protons and electrons have formed together to a neutron, hence the name (Scientific, n.d.). Now if the red supergiant was a big enough star to begin with, bigger than one that would create a neutron star, the explosion will be so immense that it will create a tiny core with enormous gravity field (Scientific, n.d.). The pull is so strong that not even light can escape its grasp resulting in a black hole (Knight, 1997).
After a star is born from a stellar nebula it can take one of two paths depending on its mass, these being an average star or massive star. Average stars have a longer life cycle as they burn their fuel slower than more massive stars (Knight, 1997). Since they have a smaller mass they don’t experience as much gravity therefore, they don’t have to produce as much gas pressure to push back to create an equilibrium (Pogge, 2006). During this stage of equilibrium the stars wither, average or massive, this is considered part of the main sequence. This equilibrium becomes compromised, as nuclear fusion slows down from lack of hydrogen present. Both average and massive stars at this stage begin to fuse helium causing the star to collapse leaving a hot core with an outer surface that begins to expand and cool (Knight, 1997). The stars can expand to be 100 times larger than the original stars surface area (Knight, 1997). Average stars become red giants, red indicating a cooler temperature and giant indicating that it has expanded. Massive stars become red supergiants an example would be Betelgeuse located in the constellation Orion. Eventually, the outer surface becomes separated and at this point is considered a planetary nebula. A planetary nebula has nothing to do with a planet it can; however, it can be mistaken to look like one. The small, white, and initially hot core, known as a white dwarf, is left to cool until it turns into a black dwarf where no more light is given off (Scientific, n.d.). A red supergiant similarly begins to run out of hydrogen but when it collapses it is in the form of an explosion referred to as a supernova. The remnants of the explosion can leave behind a neutron star or a black hole. As one would imagine with an explosion, matter gets spread out everywhere. But in this case there is also a small core left behind that is so compact the protons and electrons have formed together to a neutron, hence the name (Scientific, n.d.). Now if the red supergiant was a big enough star to begin with, bigger than one that would create a neutron star, the explosion will be so immense that it will create a tiny core with enormous gravity field (Scientific, n.d.). The pull is so strong that not even light can escape its grasp resulting in a black hole (Knight, 1997).
Figure #3
(Knight, 1997)
Our Sun
Our sun, sol, was formed over four and a half billion years ago but is currently only in the middle of its life (Facts, 2000). It is currently an average star that is part of the main sequence and it is actually pretty average but to be precise it is slightly cooler, 5,790 degrees Celsius, and smaller, diameter of 870,000 miles, than the average star. It’s life cycle will consist of becoming a red giant, then planetary nebula, and lastly a white dwarf, see life cycle above for more information. It is the star that all the planets in our solar system revolve around; therefore it is the star that we are the closest to. It is a yellow star with a spectral type of G2 and a luminosity of 1, which can be used to chart it on a HR diagram. An HR diagram is a chart where you can plot stars in comparison to luminosity and spectral type and/or absolute magnitude and temperature. It is important to note that without the sun life on earth, as we know it may not exist as it provides energy to producers that transform it in to forms of energy that we can use. It also gives us warmth and light.
(Periodic, 1997)
References:
Dejoie, J., & Truelove, E. (n.d.). Stars. StarChild. Retrieved December 4, 2011, from http://starchild.gsfc.nasa.gov/docs/StarChild/universe_level1/stars.html
Facts About the Sun. (2000). Great Balls of Fire. Retrieved December 4, 2011, from http://library.thinkquest.org/J002231F/Sun/factsaboutthesun.htm
Knight, J. D. (1997). Stars. Sea and Sky. Retrieved December 4, 2011, from http://www.seasky.org/celestial-objects/stars.html
Periodic Table (1997). Chem4kids. Retrieved December 4, 2011, from http://www.chem4kids.com/files/elements
Pogge, R. (2006, January 15). The Internal Structures of Stars. Department of Astronomy. Retrieved December 5, 2011, from http://www.astronomy.ohio-state.edu/~pogge/Ast162/Unit2/structure.html
Scientific Background. (n.d.). Montana State University. Retrieved December 4, 2011, from http://btc.montana.edu/ceres/html/LifeCycle/starsbackground.htm
Our sun, sol, was formed over four and a half billion years ago but is currently only in the middle of its life (Facts, 2000). It is currently an average star that is part of the main sequence and it is actually pretty average but to be precise it is slightly cooler, 5,790 degrees Celsius, and smaller, diameter of 870,000 miles, than the average star. It’s life cycle will consist of becoming a red giant, then planetary nebula, and lastly a white dwarf, see life cycle above for more information. It is the star that all the planets in our solar system revolve around; therefore it is the star that we are the closest to. It is a yellow star with a spectral type of G2 and a luminosity of 1, which can be used to chart it on a HR diagram. An HR diagram is a chart where you can plot stars in comparison to luminosity and spectral type and/or absolute magnitude and temperature. It is important to note that without the sun life on earth, as we know it may not exist as it provides energy to producers that transform it in to forms of energy that we can use. It also gives us warmth and light.
(Periodic, 1997)
References:
Dejoie, J., & Truelove, E. (n.d.). Stars. StarChild. Retrieved December 4, 2011, from http://starchild.gsfc.nasa.gov/docs/StarChild/universe_level1/stars.html
Facts About the Sun. (2000). Great Balls of Fire. Retrieved December 4, 2011, from http://library.thinkquest.org/J002231F/Sun/factsaboutthesun.htm
Knight, J. D. (1997). Stars. Sea and Sky. Retrieved December 4, 2011, from http://www.seasky.org/celestial-objects/stars.html
Periodic Table (1997). Chem4kids. Retrieved December 4, 2011, from http://www.chem4kids.com/files/elements
Pogge, R. (2006, January 15). The Internal Structures of Stars. Department of Astronomy. Retrieved December 5, 2011, from http://www.astronomy.ohio-state.edu/~pogge/Ast162/Unit2/structure.html
Scientific Background. (n.d.). Montana State University. Retrieved December 4, 2011, from http://btc.montana.edu/ceres/html/LifeCycle/starsbackground.htm