# Oscillation , space

In the middle of empty space two equal masses, M = 2.1 solar masses, lie fixed on a horizontal line separated by a distance D = 8.4 AU. Halfway between the masses lies a third mass. The third mass is displaced vertically a distance y where y << D. Due to the gravitational attraction from the other two masses, the third mass will be pulled back toward the line. The subsequent motion of the third mass will be approximately simple harmonic. Determine the period of the motion in years.

Please derive a equation to solve this problem