Why are there upper and lower limits to the mass of Main-Sequence stars?
• The upper limit of around 80 MSun is simply due to the pressure of photons. At very high luminosity, the photons literally blow the outer layers of the star off. • The lower limit is set by the initial GPE of a collapsing cloud and resulting central temperature at the main sequence. Below about 0.08 MSun, the central temperature of the collapsed object never reaches the 107 K required for starting the fusion fires and the object never reaches stardom – these objects are called brown dwarfs. • All the above is star formation theory that was very difficult to check out with observations. Two things changed this: Infrared detectors and the Hubble Space Telescope. There have also been a few surprises resulting from the observations of the past 10 years. • Infrared Observations There are two reasons the observations at wavelengths between 10 microns and 2 microns are important. • Protostars and proto-stellar clouds are cool and emit much of their radiation a long wavelengths. • Dust absor
