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ismstarformationshort

# ismstarformationshort - How Long do Stars Live(as Main...

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1 Energy mosquito lands on your arm = 1 erg Firecracker = 5 x 10 9 ergs 1 stick of dynamite = 2 x 10 13 ergs 1 ton of TNT = 4 x 10 16 ergs 1 atomic bomb = 1 x 10 21 ergs Magnitude 8 earthquake = 1 x 10 26 ergs Earth’s daily solar input = 1 x 10 29 ergs Planet cracker = 1 x 10 32 ergs Luminosity of the sun = 4 x 10 33 ergs/sec How Long do Stars Live (as Main Sequence Stars)? A star on Main Sequence has fusion of H to He in its core. How fast depends on mass of H available and rate of fusion . Mass of H in core depends on mass of star . Fusion rate is related to luminosity (fusion reactions make the radiation energy). lifetime α mass (mass) 3 Because luminosity α (mass) 3 , lifetime α or 1 (mass) 2 So if the Sun's lifetime is 10 billion years, a 30 M Sun star’s lifetime is only 10 million years. Such massive stars live only “brieFy”. mass of core fusion rate mass of star luminosity α So, Clicker Question: The HR diagram is a plot of stellar A: mass vs diameter. B: luminosity vs temperature C: mass vs luminosity D: temperature vs diameter Clicker Question: What would be the lifetime of a star one tenth as massive as our sun? A: 1 billion years = 10 9 years B: 10 billion years = 10 10 years C: 100 billion years = 10 11 years D: 1 trillion years = 10 12 years Clicker Question: What would be the lifetime of a star three times more massive as our sun? A: 1 billion years = 10 9 years B: 10 billion years = 10 10 years C: 100 billion years = 10 11 years D: 1 trillion years = 10 12 years

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2 The Interstellar Medium (ISM) of the Milky Way Galaxy Or: The Stuff (gas and dust) Between the Stars Stars form out of it. Stars end their lives by returning gas to it. The ISM has: a wide range of structures a wide range of densities (10 -3 - 10 7 atoms / cm 3 ) a wide range of temperatures (10 K - 10 7 K) Why study it? Compare density of ISM with Sun or planets: Sun and Planets: 1-5 g / cm 3 ISM average: 1 atom / cm 3 Mass of one H atom is 10 -24 g! So ISM is about
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ismstarformationshort - How Long do Stars Live(as Main...

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