Chapter 21, Problem 7E

The evolutionary track for a star of 1 solar mass remains nearly vertical in the H−R diagram for a while (see Figure 21.12). How is its luminosity changing during this time? Its temperature? Its radius?

Figure 21.12 Evolutionary Tracks for Contracting Protostars. Tracks are plotted on the H−R diagram to show how stars of different masses change during the early parts of their lives. The number next to each dark point on a track is the rough number of years it takes an embryo star to reach that stage (the numbers are the result of computer models and are therefore not well known). Note that the surface temperature (K) on the horizontal axis increases toward the left. You can see that the more mass a star has, the shorter time it takes to go through each stage. Stars above the dashed line are typically still surrounded by infalling material and are hidden by it.