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Author
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Topic: astrofizix
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grumpy
Sarge
Member # 1912
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posted 05-09-2005 01:19 AM
    
any comments appreciated!!!q1) why does the theoretical mass-luminosity relation depend either not at all or very slightly on the nuclear energy generation though it is usually the nuclear energy generation that suppliles the energy for the star's Luminosity? q2) when a layer is convectively unstable, why is it reasonable to assume that the temperature gradient is very nearly adiabatic?
thanx homies
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Posts: 1561 | From: girls! computers, drinking, partying | Registered: Feb 2000 | IP: Logged
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WillyTrombone
Sarge
Member # 27
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posted 05-09-2005 03:48 AM
1) Think of it in terms of the Bohr-Oppenheimer approximation. Yes, the energy is made from nuclear reactions. BUT, there are electrons in the cooler matter lying outside the fusion reaction just waiting to be stimulated. Hence, all the photons and phonons released by the nuclear reactions (which will be mostly in the x-ray region, IIRC, with maybe some UV-C and gamma rays) are essentially filtered by cooler matter before exiting the star and the signals we receive are from the re-emission of energy from this peripheral matter. At least, that's my guess. 2) I'm not sure exactly what you mean by convectively unstable. Taking it to mean that there is little exchange of mass across regions of significantly different thermal states, then the assumption of adiabatic conditions is inherently being made since the only exchange of energy will be radiative in nature, and hence of a small degree (and the source of most of the deviation from the prediction of an adiabatic system with the rest being due to the small amount of heat conduction available from the small-scale stabilities that will probably be present in the chaotic patterns of a real-life system) -------------------- signature
Posts: 2844 | From: the edge of forever | Registered: Jun 1999 | IP: Logged
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Wolfie
Sarge
Member # 1698
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posted 05-09-2005 07:58 PM
I think that's only a theory and not proven thus far. I'm studying for my geophysics exam tomorrow.  Questions in the past papers are something like..."Give an account of an experiment to measure the attraction of a mountain as a means of estimating the mass of the Earth"
(I take it this as something to do with Pratt and Bouger) and "Sketch a depth-profile of the differentail stress that could be supported in the continental lithosphere and explain why it is described as a strong-weak-strong sandwich"
(I have no idea what that's on about) That said, Geophysics is only my outside course, so it only matters if I pass, not whether I do well. -------------------- Draw a crazy picture,
Write a nutty poem,
Sing a mumble-grumble song,
Whistle through your comb.
Do a loony-goony dance
'Cross the kitchen floor,
Put something silly in the world
That ain't been there before.
-Put Something In, Shel Silverstein
Posts: 786 | From: Cold place that rains all the time | Registered: Jan 2000 | IP: Logged
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grumpy
Sarge
Member # 1912
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posted 05-10-2005 08:18 PM
thanx dub-T!sounds like money to me. good luck w/ your exam wolfchica! i gotta test in geo303 - Dinosaurs!! tomorrow. may da force be wit chu! --------------------
Posts: 1561 | From: girls! computers, drinking, partying | Registered: Feb 2000 | IP: Logged
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AcidWarp
Sarge
Member # 997
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posted 05-11-2005 01:45 AM
grumpy, don't you ever, and I mean EVER profane that phrase by using 'wit chu'.-------------------- “I have noticed even people who claim everything is predestined, and that we can do nothing to change it, look before they cross the road.” “Intelligence is the ability to adapt to change.” --Dr. Stephen Hawking.
Posts: 4363 | From: Waterloo, Ontario | Registered: Nov 1999 | IP: Logged
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