Monday, February 6, 2012

What is the period of this binary star system?

The mass of one star is 1 solar mass, the mass of the second star is 2 solar masses, and the distance between them is 100 * solar radius.What is the period of this binary star system?Use Kepler's third law.

P^2 = 4 pi^2 d^3/(G(M1+M2))



If we use Years, Astronomical Units and Solar Masses as units this reduces to

P^2 = d^3/(M1+M2)



So we have P = sqrt (100^3 / (1+2)) = 577 years.What is the period of this binary star system?First use this equation to find the stars' barycenter:

R1= A x (M2/(M1+M2)

M1= mass of the more massive stars

M2= mass of the less massive star

A= the distance between the two stars

R1= is the distance of the 1 solar mass star from its barycenter.



R1= 100 x (2/(2+1)

(2/(2+1)= 0.67

0.67 x 100=67=R1

67 solar radii = the distance of the 1 solar mass star from the barycenter.

to find the distance between the barycenter and the 2 solar mass star you do 100-67=33

33 solar radii= The distance of the 2 solar mass star from the barycenter

To find the orbital period for each stars, do each of the distances to the 1.5 power.

67^1.5=548.42

33^1.5=189.57

P of the 1 solar mass star= 548.42 years

P of the 2 solar mass star= 189.57 years

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