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Math Help - Planetary system

  1. #1
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    Exclamation Planetary system

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


    Itís 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?


    (Seconds between planetary systems being born)



    I've been getting numbers all over the place for the second part, please help!

    Thanks!
    Last edited by Oldspice1212; November 7th 2012 at 02:18 AM.
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  2. #2
    MHF Contributor MarkFL's Avatar
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    Re: Planetary system

    Multiply the result from part a) by 100 billion, then convert years to seconds.
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  3. #3
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    Re: Planetary system

    6.31139e18 that seems outrageously large?!
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  4. #4
    MHF Contributor MarkFL's Avatar
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    Re: Planetary system

    I get about 6.3 per second. Informally, you want to multiply 2 times 100 billion, then divide by the number of seconds in a year.
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  5. #5
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    Re: Planetary system

    Nope that didn't work :\

    6.3 seconds between planetary systems being born. This seems odd.

    Unless I divide 6.3/ 60 seconds = 0.105 s does this make sense?
    Last edited by Oldspice1212; November 7th 2012 at 01:56 AM.
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  6. #6
    MHF Contributor MarkFL's Avatar
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    Re: Planetary system

    No, I mean about 6.3 per second, assuming the result from the first part of the question was 2 per year, which I did not check.
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  7. #7
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    Re: Planetary system

    Ah we'll I'm getting 6337.7 now haha
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