Main_Sequence

# Main_Sequence - Main Sequence Stars Thermal and...

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Main Sequence Stars

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Thermal and Gravitational Energy Two large stores of energy in a star are its internal heat ( thermal energy) and its gravitational energy. The heat stored in a gas is simply the energy of motion ( kinetic energy) of the particles that compose it. If the speeds of these particles decrease, the loss in kinetic energy is radiated away as heat and light.
Conservation of Energy The source of heat energy is the chemical burning of objects. Even if the immense mass of the Sun consisted of burnable material, it could not produce energy at its present rate for more than a few thousand years. Geologists have found fossils in rocks that are 3.5 billion years old. Therefore, the Sun must have been heating the Earth nearly that long in order for life to have been maintained. In the 19th century, scientists used the Law of Conservation of Energy to look for a source of energy for the Sun. The law of conservation of energy simply says that energy cannot be created or destroyed, but can be transformed. The reverse is also true. Mechanical motion can be transformed into heat.

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Gravitational Energy The outer layer of the Sun is a gas, and the temperature is a measure of the atoms’ speeds. If this layer were to fall inward, the atoms would acquire an additional velocity (potential energy is converted to kinetic energy). The star would contract and the atoms would move closer together, increasing the number of collisions, and the temperature would increase. A contraction rate of 40 m/yr would be enough. The amount of energy that has been released since the pre-solar cloud began to contract is on the order of 10 42 joules. This is the amount that the Sun could have converted to thermal energy. Since the present luminosity is 3.83 x 10 26 watts (J/s) or about 10 34 J/yr, this mechanism could have kept the Sun going for 100 million years, but this is much less than the age of the Solar System.
Mass, Energy, and Special Relativity Einstein’s Special Theory of Relativity says that mass and energy are equivalent: E = m c 2 Mass can be converted to energy, and energy can be converted to mass. The conversion of even a small amount of mass can release great amounts of energy.

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