The Universe Essay Research Paper Student — страница 4

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After the core has burned out, the surface will cool and turn red. After a star has been in its main sequence phase long enough to use up all of the hydrogen fuel in its core, the star’s core will collapse and its outer layers will expand and cool, producing a very large, reddish colored star known as a red giant. During the red giant phase, helium is consumed in the hot, high pressure core of the star until all of the helium is used up, at which time the star again becomes unstable and evolves further into a white dwarf, a neutron star, or a black hole. 31. List the spectral types into which stars are grouped, and state into which type the Sun has been classified. Your Answer: hottest to coolest:OBAFGKM, sun is a G star. The spectral classes into which stars are classified by

their surface temperatures from hottest to coolest are; O, B, A, F, G, K, M. Our Sun has a relatively cool surface, about 6000 K, and is classified as a G type star. 32. What is a supernova? Your Answer: Explosion which occurs when a core of a star collapses. A supernova is a tremendous explosive event that occurs when the core of a massive main sequence star collapses with such energy that the star may completely destroy itself. This may occur after the nuclear fusion reactions in the core of the star have used up all available fuel. 33. Describe a simplified H-R diagram, and indicate the location of the following: main-sequence stars, red giants, and white dwarfs. (Draw a simple diagram if you wish.) Your Answer: The diagram plots the absolute magnitude of stars. An H-R diagram

is a plot of the absolute magnitudes of many stars as a function of their spectral classes (this is essentially the same thing as their surface temperatures). Such a plot shows all of the main sequence stars in a diagonal pattern, with the heaviest of them at the upper left corner and the less massive ones in the lower right-hand corner of the diagram. Red giant stars are plotted above and to the right of the main sequence, and white dwarf stars are below and near the center of the main sequence plot. See Figure 18.11 in the textbook for a pictorial representation of an H-R diagram. 34. Explain how galaxies are classified, and give the names for the three main classes of galaxies. Your Answer: They are classified by how they look from the Earth. Three classes are elliptical,

spiral, and irregular. Galaxies are classified by the way that they appear as seen from Earth. Galaxies that have a clearly spherical or flattened spherical shape are called elliptical galaxies, and those showing a tight or loose spiral structure are called spiral galaxies. Any galaxies that cannot be classified as elliptical or spiral are designated as irregular galaxies. 35. What is the cosmological redshift, and what does it suggest about the origin of the universe? Your Answer: A shift in galaxies toward the low frequency. From this we can tell the universe is expanding and began with an explosion, the Big Bang. The cosmological redshift is a shift in the spectrum lines of galaxies toward the low-frequency (red) end of the electromagnetic spectrum. It is believed that this

shift in spectrum lines is the result of the overall expansion of the universe. This redshift along with the discovery of the 3-K cosmic background radiation and the observed mass ratio of hydrogen to helium throughout the universe all point to a model in which the universe was created in a gigantic explosion, the Big Bang, and we now see the entire 320