1. Not finding help here? Sign up for a free 30min tutor trial with Chegg Tutors
    Dismiss Notice
Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Kepler's Third Law and Motion of Two Point Masses

Tags:
  1. Sep 18, 2016 #1
    I'm trying to work through some equations in the paper 'Gravitational Radiation and the Motion of Two Point Masses' (Peters, 1964) but I can't get out the right values

    1. The problem statement, all variables and given/known data

    For a binary star system with each mass = 1 solar mass, the equations give the results:
    Separation ~ 10 solar radii
    Period ~ 4.5 days
    Lifetime for decay ~ 3x1012 years

    2. Relevant equations
    T = a4/4B
    B = (64/5)G3m1m2(m1+m2)/c5

    3. The attempt at a solution
    Using solar mass = 1.989 x 1030kg,
    solar radius = 695700 km
    G = 6.67408 x 10-11 m3kg-1s-2
    c = 3 x 108 ms-1

    I get B = (1/(3 x 108)5)(64/5)(6.67408 x 10-11)3 x 2 x 1.989 x1030 x 103 = 6.229 x 10-42

    T = (10 x (695700 x 1000))4/4B = ~1.12 x 1051 s, which isn't at all near 3 x 1012 years :( Help?
     
  2. jcsd
  3. Sep 18, 2016 #2
    Oh, also regarding Kepler's third law. My lecture notes give it as

    (G/4pi2)(m1 + m2) t2=a3

    where t is orbital period in years, masses are in solar units, and a is in au. This formula also isn't working for me yet?
     
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook

Have something to add?
Draft saved Draft deleted