1) Astronomers discover a binary star system that has period of 90 days. The binary star system consists of two equal mass stars each with a mass twice the sun's. They rotate about the center of mass at the midpoint between them. How far apart are the two stars?
2) Three stars each with a mass of our sun, form an equilateral triangle with sides 1* 10^12 m long. The triangle has to rotate because otherwise the stars would collide. What is the period of rotation?
The Attempt at a Solution
There doesn't seem to me to be any clear pivot or mass around which the stars orbit, and that's what baffles me. I thought about pretending they were connected by a massless string and calculating the moment of inertia, and then using rotational kinetic energy, but I'm not sure how to start
#2 I think I'll have a better grasp on this after figuring out #1