ast3018lecturestarform

ast3018lecturestarform - 1 It's lovely to live on a raft We...

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Unformatted text preview: 1 It's lovely to live on a raft. We had the sky up there, all speckled with stars, and we used to lay on our backs and look up at them, and discuss about whether they was made or only just happened . The Adventures of Huckleberry Finn by Mark Twain (1884; pg. 159). Is star formation occurring now? !4UFMMBS!TUSVDUVSF!BOE!FWPMVUJPO Expanding OB associations Discovery of the Interstellar medium First Proof: Nuclear Powered Stars In 1938 Bethe and others worked out the fusion reactions (CNO and p-p cycles) that powered stars and demonstrated that: Stars are thermo-nuclear reactors which fuse the primary product of the big bang into heavier elements of the periodic table releasing enormous amounts of energy in the process. Massive OB stars burn nuclear fuel at such prodigious rates that their lifetimes must be less than 10 7 years, considerably less than the age of the universe. Hans Bethe 1906 - Second Proof: Expanding OB Associations Ambartsumian (1949) identified loose associations of OB stars with stellar densities less than the general galactic field and he demonstrated that such groups are unstable and will dissolve into the field on timescales of 10 7 years, considerably less than the age of the Galaxy. V. A. Ambartsumian 1906 - 1996 Third Proof: A Hydrogen-rich Interstellar Medium The discovery of pervasive HI emission in the galaxy by Ewen and Purcell in 1951 convincingly demonstrated that the raw material for building stars existed in substantial concentrations between the stars. Existence of vast Interstellar Medium of the same composition as stars 2 • ORION “...ein Loch im Himmel!” William Herschel 1738-1822 Caroline Herschel 1750-1848 An Opening in the heavens “...for instance, in the body of the Scorpion is an opening, or hole, ...I found it while I was gauging in parallel from 112 to 114 degrees north of polar distance…As I approached the Milky Way the gauges were gradually running up …when all of a sudden, they fell to nothing! William Herschel 1785, Phil. Trans. LXXV, pp. 213-266 An Opening in the heavens “...It is remarkable, that one of the richest and most compressed clusters of small stars I remember to have seen, is situated on the western border of it, and would almost authorise a suspicion that the stars, of which it is composed, were collected from that place and had left the vacancy.” William Herschel 1785, Phil. Trans. LXXV, pp. 213-266 3 “Dear Nephew, As soon as your instrument is erected I wish you would see if there is not something remarkable in the lower part of the Scorpion to be found...” John Herschel 1792-1871 Feldhausen, South Africa:1834 “I have not been unmindful of your hint about Scorpio. I am now rummaging the recesses of that constellation and find it full of beautiful globular clusters.” John Herschel 1792-1871 “It is not Clusters of Stars I want you to discover in the body of the Scorpion (or thereabouts) for that does not answer my expectation, remembering having once heard your father...expectation, remembering having once heard your father....
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This note was uploaded on 07/28/2011 for the course AST 3018 taught by Professor Lada during the Fall '08 term at University of Florida.

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ast3018lecturestarform - 1 It's lovely to live on a raft We...

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