Stellar Evolution Essay -- Astronomy Space Cosmos Papers

Stellar Evolution A star begins as nothing more than a very light distribution of interstellar gases and dust particles over a distance of a few dozen lightyears. Although there is extremely low pressure existing between stars, this distribution of gas exists instead of a true vacuum. If the density of gas becomes larger than .1 particles per cubic centimeter, the interstellar gas grows unstable. Any small deviation in density, and because it is impossible to have a perfectly even distribution in these clouds this is something that will naturally occur, and the area begins to contract. This happens because between about .1 and 1 particles per cubic centimeter, pressure gains an inverse relationship with density. This causes internal pressure to decrease with increasing density, which because of the higher external pressure, causes the density to continue to increase. This causes the gas in the interstellar medium to spontaneously collect into denser clouds. The denser clouds will contain molecu lar hydrogen (H2) and interstellar dust particles including carbon compounds, silicates, and small impure ice crystals. Also, within these clouds, there are 2 types of zones. There are H I zones, which contain neutral hydrogen and often have a temperature around 100 Kelvin (K), and there are H II zones, which contain ionized hydrogen and have a temperature around 10,000 K. The ionized hydrogen absorbs ultraviolet light from it’s environment and retransmits it as visible and infrared light. These clouds, visible to the human eye, have been named nebulae. The density in these nebulae is usually about 10 atoms per cubic centimeter. In brighter nebulae, there exists densities of up to several thousand atoms per cubic centimete... ...J. Stellar Evolution. London: Pergamon Press, 1967. Shklovskii, Iosif S. Stars: Their Birth, Life, and Death. Moscow: Central Press for Literature in Physics and Mathematics, 1975. Livio, Mario. Unsolved Problems in Stellar Evolution. Cambridge: The Cambridge University Press, 2000. Websites: http://www.wikipedia.org/wiki/Astronomy_and_astrophysics Encyclopedia of Astronomy Terms http://imagine.gsfc.nasa.gov/docs/science/how_l1/spectral_what.html NASA’s Introduction to Spectral Analysis http://zebu.uoregon.edu/textbook/se.html Hypertext Book on Stellar Evolution @ The University of Oregon http://hyperphysics.phy-astr.gsu.edu/hbase/starlog/staspe.html#c1 Star Spectral Classifications @ Georgia State University http://oposite.stsci.edu/pubinfo/PR/96/22/pulsars.html How Pulsars Are Formed @ The Space Telescope Science Institute