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Luminosity physics question

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1. Homework Statement
Show that the Hubble profile of surface brightness

[tex]I(r) = I_0 \left(1+\frac{r}{R}\right)^{-2}[/tex]

leads to an infinite total luminosity. r is the distance from the center and R is a constant.


2. The attempt at a solution
For large r this is related as

[tex]I(r) \propto r^{-2}[/tex]

but how is the surface brightness related to the total luminosity?
 

Answers and Replies

dextercioby
Science Advisor
Homework Helper
Insights Author
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Can't you find it in the textbook ? Even though the problem seems to be purely mathematical (basically a computation which gives infinity as its result), you have problems in the conceptual domain. Well, the/my advice is to look again in the book.
 
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I have, all there is about this is one half page of text.
 
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This is still a problem... Haven't anyone dealt with this before?
 

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