3 The masses of stars
In the previous section, you saw that the overall luminosity of a star depends primarily on two factors: its temperature and its size. In order to explain the wide range of luminosities along the main sequence on the HR diagram, the more luminous stars must be hotter and larger, and the less luminous stars correspondingly cooler and smaller. This starts to provide a clue as to why the temperatures and luminosities of stars vary in the first place.
The answer lies in the mass of the star. As stars form from clouds of condensing gas, different amounts of material collapse down to form each star. Some contain more material and are heavier (more massive) and some contain less material and are lighter (less massive). In this section, you explore how the mass of a star influences its temperature and luminosity.