Binary Stars Interactive (*.swf)
McGraw-Hill Online Learning Center
Astronomy 10 learning goal Q10.2
Begin with setting M_A = 0.5 solar masses, M_B = 5.0 solar masses, and separation distance = 20 solar radii. Point out that the more massive star B is closer to the center of mass/rotation axis, while the less massive star A is farther away. Ask the students which star will eventually reach the end of its main sequence lifetime first, and why (star B, as it is more massive), and which star will have the larger Roche lobe (star B, as it is both more massive and slower in orbital speed, resulting in less centrifugal force, which counteracts gravity).
If the separation distance is decreased to 7.0 solar radii, the Roche lobes of both stars shrink, as they will both have faster orbital speeds (and thus stronger centrifugal forces, which decreases the volume of space that matter will accelerate in towards either star). The more massive star B still has a larger Roche lobe than star A.
http://highered.mcgraw-hill.com/olcweb/cgi/pluginpop.cgi?it=swf::100%::100%::/sites/dl/free/007299181x/78778/Binary_Nav.swf::Binary%20Stars%20Interactive
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