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B Characteristic age of pulsars

  1. Mar 14, 2016 #1
    Hi everyone.
    I'm trying to derive the formula for the characteristic age of a pulsar.

    What i'm starting with is the following differential equation.
    dP/dt=K*P2-n

    What i think is odd, is several places they say solving this differential equation gives the following solution.
    T=(P/((n-1)*dP/dt))*(1-(P0/P)n-1

    Here is a picture of the equation too: df1.gif

    But how do you get from equation 1. to this equation.
    Please help me out, if you could explain it step by step, i would really appreciate it.
    Because it doesn't make sense if you're trying to seperate both variables and integrate?
     
    Last edited: Mar 14, 2016
  2. jcsd
  3. Mar 15, 2016 #2
    Hope this helps:
    [itex]\dot{P}=\frac{dP}{dt}=kP^{2-n}[/itex]
    [itex]dt=\frac{dP}{kP^{2-n}}[/itex]
    [itex]\tau=t-t_{0}=\int_{P_{0}}^P \frac{dP}{kP^{2-n}}=\frac{1}{k}\frac{P^{n-1}-P_{0}^{n-1}}{n-1}=\frac{P^{n-1}}{k(n-1)}[1-(\frac{P_{0}}{P})^{n-1}][/itex]
    [itex]k=\frac{\dot{P}}{P^{2-n}}[/itex]
    [itex]\tau=\frac{P}{(n-1)\dot{P}}[1-(\frac{P_{0}}{P})^{n-1}][/itex]
     
  4. Mar 15, 2016 #3

    Student100

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    In some texts this is considered the "true" age of pulsar, although the true age would also have k and n as functions of time.

    The characteristic age is typically when k is kept as constant, n = 3, and ##\frac{P_0}{P} = 0##, this is an overestimation, but a decent approximation.

    Have you read M&T, Pulsars?
     
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