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Planetary system

  1. Nov 7, 2012 #1
    Hey guys so I'm kind of stuck on the second part of this question, here it is.

    It’s possible to make a rough estimate of how often planetary systems form by making some basic assumptions. For example, if you assume that the stars we see have been born at random times over the last 10 billion years, then the rate of star formation is simply the number of stars we see divided by 10 billion years. The fraction of stars with detected extrasolar planets is at least 5%, so this factor can be multiplied in to find the approximate rate of formation of planetary systems.


    1. Using these assumptions, how often does a planetary system form in our galaxy? (Our galaxy contains at least 100 billion stars.)

    answer was 2 year/planetary systems

    2. How often does a planetary system form somewhere in the observable universe, which contains at least 100 billion galaxies?

    (In seconds between planetary systems being born)

    Need help with this second part, thanks!
     
    Last edited: Nov 7, 2012
  2. jcsd
  3. Nov 7, 2012 #2

    SammyS

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    Many stars have lifetimes much much less than 10 billion years. For some the lifetime is just a few million years.

    Others have lifetimes well in excess of 10 billion years. As much as six to twelve trillion years.
     
  4. Nov 7, 2012 #3

    Simon Bridge

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    Well how did you do the first part?
    Why can't you use the same method for the second part?
     
  5. Nov 7, 2012 #4
    I keep getting some ridiculous number >.<
     
  6. Nov 7, 2012 #5

    haruspex

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    It might be astonishing but not ridiculous. What do you get?
     
  7. Nov 7, 2012 #6

    Simon Bridge

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    I agree - but also show your working/reasoning.
     
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