Mass Beyond the Main Sequence

Brown dwarfs are now being discovered in significant numbers which means that at last it is possible to be quantitative about their number density and thus their contribution to the stellar neighbourhood. Overall the emerging picture is one of rising mass function into the brown dwarf regime though with a total brown dwarf mass contribution of around 10 percent that due to stars. Contrary to expectation, these stars too small to burn nuclear fuel, do not contribute significantly to our Galaxy's missing mass. However, their properties are more complex than expected and thus there are considerable uncertainties to overcome before a robust determination of the brown dwarf mass function is possible.