 Once the mass of enough binary stars were calculated, it became possible to plot mass versus luminosity on a graph. Here's what they found. Instead of having any combination of mass and luminosity, we see that stars fall on the line from low mass, low luminosity, to high mass, high luminosity. But it is not linear. Each time the mass is doubled, the luminosity goes up 11 times. This relationship seems to work for most stars that aren't too massive. Note that this is an empirical relationship. We don't start with an equation and plot its graph. We observe events to create the graph and then find an equation that would have created a graph that looks like the one or fits the one we observed. Now back to stars again. . . . . . . .