List of Most Massive Stars - Uncertainties and Caveats

Uncertainties and Caveats

Most of the masses listed below are contested and, being the subject of current research, are constantly being revised.

The masses listed in the table below are inferred from theory, using difficult measurements of the stars’ temperatures and absolute brightnesses. All the listed masses are uncertain: both the theory and the measurements are pushing the limits of current knowledge and technology. Either measurement or theory, or both, could be incorrect. For example, VV Cephei could be between 25–40 M_☉, or 100 M_☉, depending on which property of the star is examined.

Massive stars are rare; astronomers must look very far from the Earth to find one. All the listed stars are many thousands of light years away, and that alone makes measurements difficult. In addition to being far away, many stars of such extreme mass are surrounded by clouds of outflowing gas; the surrounding gas obscures the already difficult-to-obtain measurements of the stars’ temperatures and brightnesses, and greatly complicates the issue of measuring their internal chemical compositions. For some methods, different chemical composition leads to different mass estimates. In addition, the clouds of gas obscure observations of whether the star is just one supermassive star, or instead a multiple star system. A number of the stars below may actually consist of two or more companions in close orbit, each star being massive in itself, but not necessarily supermassive. Alternatively, it is possible for a multiple-star system to still have one (or more) supermassive star, with one (or more) much smaller companion(s). Without being able to see inside of the surrounding cloud, it is difficult to know which scenario might be the case.

Amongst the most reliable listed masses are NGC 3603-A1 and WR20a+b, which were obtained from orbital measurements. They are both members of (different) binary star systems, and it is possible to measure in both cases the individual masses of the two stars by studying their orbital motion, via Kepler's laws of planetary motion. This involves measuring their radial velocities and also their light curves, as both stars are eclipsing binaries. The derivation of binary masses requires relatively limited information about the orbital parameters, but one key value that isn't always accurately known is the inclination. Without this only a minimum value for the masses can be derived, so several binaries are shown with masses as greater than a particular value.