An evolutionary track charts a star or protostar\'s changing position within its
ID: 235045 • Letter: A
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An evolutionary track charts a star or protostar's changing position within its parent cluster. More massive stars form more rapidly. The least massive stars will remain stable for a trillion years. While more massive than most of our neighbors, our Sun is still technically a low- mass star. Brown dwarfs take a long time to form, but will eventually become visible as stars on the lower main sequence. About 90 percentage of the star's total life is spent on the main sequence. As a star evolves away from the main sequence, it gets larger. As a star evolves away from the main sequence, it gets hotter. Our Sun will first become a red giant, then a white dwarf, and finally a brown dwarf. A star may undergo two or more red giant expansion stages. Our Sun should become a planetary nebula in another five billion years. White dwarfs were once the central star of planetary nebulae. The density of white dwarfs is about a million times that of our Sun. A nova occurs when a white dwarf is fed enough matter to reach its Chandrasekhar limit by its swollen companion. Stellar evolution in binary stars has much the same outcome as in isolated stars. A 100 million year old open cluster will no longer contain any O type stars. Globular clusters are dominated by bright red supergiants at the top right of the H-R diagram. Most stars form as members of groups or clusters.Explanation / Answer
1. False : Each curve in HR Diagram, is a life track (or evolutionary track) showing how the luminosity and temperature of a single protostar changes as it gradually develops into a main sequence star.
2. True : The very massive stars form first and explode into supernova. This makes shock waves into the molecular cloud, causing nearby gas to compress and form more stars.
3. True: The very massive stars form first and explode into supernova.
4. True: Our Sun is low massive star.
5. False: Brown dwarfs lack sufficient mass required to ignite the fusion of hydrogen in their cores, and thus never become true stars.
6.True: yes 90% of life is spent on the main sequence
7.True: As the star evolve it get larger and hotter.
8. True.
9. False: In some five billion years from now, our sun can become a red giant and burned the Earth to a cinder, it can eject its own beautiful nebula and then fade away as a white dwarf star.
10 True: A star can have more than one stages of expansion.
11 True:
12 True:
13 False: Average density of matter in a white dwarf must therefore be, very roughly, 1,000,000 times greater than the average density of the Sun.
14 True : As the white dwarf's mass approaches the Chandrasekhar limit, its central density increases, and, as a result of compressional heating, its temperature also increases. This eventually ignites nuclear fusion reactions, leading to an immediate carbon detonation which disrupts the star and causes the supernova.
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