Luminosity physics question

  • #1
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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

  • #2
dextercioby
Science Advisor
Homework Helper
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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.
 
  • #3
281
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I have, all there is about this is one half page of text.
 
  • #4
281
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This is still a problem... Haven't anyone dealt with this before?
 

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