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Relativistic escape velocity

  1. Nov 9, 2016 #1
    1. The problem statement, all variables and given/known data
    Calculate the escape velocity on the surface of the neutron star in the previous problem (##m = \frac{2}{3} \cdot 2,1 \cdot M_{\odot}##; ##R = 15km##).

    Hint: Basic physics. Note, however, that the escape velocity is not going to be small when compared to the speed of light.

    2. Relevant equations
    Relativistic kinetic energy:
    \begin{equation}
    K = \gamma mc^2 - mc^2 = \sqrt{(pc)^2 + (mc^2)^2} - mc^2
    \end{equation}

    Standard Newtonian potential energy:
    \begin{equation}
    V_N = -G\frac{mM}{r}
    \end{equation}

    Relativistic potential energy:
    \begin{equation}
    V_R = ?
    \end{equation}

    3. The attempt at a solution

    My idea was to set the kinetic and potential energies to be equal, and solve for the speed as usual. The problem is, I don't know (how to derive) the expression for a relativistic potential, which I'm probably going to need because, you know, it's a neutron star we're talking about here.

    I found a source (since none of my books were of any use), that simply multiplies the standard Newtonian potential with the Lorentz-factor ##\gamma##, but I'm not sure that's allowed.

    Is it, and if so, why?
     
  2. jcsd
  3. Nov 9, 2016 #2
    Scratch everything I said. I got the wrong result because of an input error... No such thing as a relativistic potential, apparently.

    GG, calculator with a small screen.
     
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