There is a rather surprising thing afoot in many introductory astronomy texts, and many online web course notes, relating to a commonly seen but completely wrong explanation for why high-mass main-sequence stars have a much higher luminosity than low-mass main-sequence stars. You would really think this would be a basic question, and indeed its answer has been well known for about 100 years, and can still be found in all the high-level texts. But in course notes, and introductory texts, which still ought to know better, you generally find a "truthy" sounding explanation along the lines of, higher mass yields stronger gravity, greater weight, a higher temperature and pressure core, and more rapid fusion as a result. For example, if I google the question "why are high-mass main-sequence stars more luminous than low-mass main-sequence stars," the first hit does not attempt to answer the question, and the second hit is a Wiki entry that does give the correct answer but it largely plays out in the bibliography to the article, so the reader might go on to the third hit, an Astropedia entry at: http://m.teachastronomy.com/astropedia/article/Understanding-the-Main-Sequence [Broken] which asserts: " More massive stars have greater gravity that creates higher pressure in the stellar interior. The higher pressure results in higher temperature that causes higher energyoutput by the fusion process, giving both higher luminosity and higher surface temperature." The next hit does not offer an explanation, it just cites the empirical relationship, but the fifth hit, lecture notes from Lick observatory at http://www.ucolick.org/~mfduran/AY2/lectures/Class-02-21.pdf , repeats verbatim this completely wrong explanation, as though it was cut and pasted from the same source (or written by the same author?). Other websites at least put it into their own words, but they often repeat some version of that false dogma. So by this point, a student seeking an answer to this question would have found some sites that don't answer it, a Wiki entry that requires some digging to get to the right answer, and two authoritative websites that very clearly "explain" the answer by saying something completely wrong. How can we have this sorry situation in regard to such a simple question? For those who do not know why that answer is so completely wrong, the correct answer is that high-mass stars do not need to contract as much to get to fusion temperatures in their core, so they have both lower densities, and lower pressures, than lower mass main-sequence stars. That makes them bigger and leakier buckets of light, pure and simple. Yes, that's right, they have lower core pressures. Also, their luminosity is not set by their fusion rates, instead their fusion rates self-regulate to simply replace whatever light is leaking out. The luminosity is set by the rate the light leaks out, which mostly relates to the physics of thermal radiation and how it diffuses, as was known even before fusion was discovered. A somewhat awkward but basically correct version can be found at http://en.wikipedia.org/wiki/Mass–luminosity_relation , which suffices to show that the rate light diffuses out of a star depends almost exclusively on the mass of the star, period, with no reference to fusion, and certainly no false claims that high mass stars have higher core pressures. So what gives here, why are so many authoritative sources so wrong on this simple issue?