List of most massive stars
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, WR21a and WR20a, which were obtained from orbital measurements. They are 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 they 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. For eclipsing binaries, the inclination can be derived with better accuracy.
Stellar evolution 
The list only gives the inferred current masses of stars, not previous masses. A number of these and other stars may have started out with even greater masses than the listed current estimates, but have probably lost many tens of solar masses of material due to the huge amount of gas they outflow, and sub-supernova and supernova impostor explosion events.
Also there are a number of supernovae and hypernovae remnants whose precursor stars' masses can be estimated based on pre-super/hypernova observations and the energy and type of explosion. These stars would have easily appeared in this list, had they survived.
List of the most massive stars 
Known stars with an estimated mass of 25 or greater M☉. Masses are their current (evolutionary) mass, not their initial (formation) mass. The list is far from complete, although the majority of stars thought to be more than 100 M☉ are shown.
- This is the estimated initial mass when the star formed. The current mass is unclear, obviously less. A crude WR mass-luminosity estimate would point to a current mass of 70-130.
- This unusual measurement was made by assuming the star was ejected from a three-body encounter in NGC 3603. This assumption also means that the current star is the result of a merger between two original close binary components. The mass is consistent with evolutionary mas for a star with the observed parameters
- These are minimum values with the orbital solution still uncertain.
Black holes 
Black holes are the end point evolution of massive stars. Technically they are not stars, as they no longer generate heat and light via nuclear fusion in their cores.
- Stellar black holes are objects with approx. 4-15 M☉.
- Intermediate-mass black holes range from 100-10000 M☉.
- Supermassive black holes are in the range of millions or billions M☉.
Eddington's size limit 
The limit on mass arises because stars of greater mass have a higher rate of core energy generation, their luminosity increasing far out of proportion to their mass. For a sufficiently massive star the outward pressure of radiant energy generated by nuclear fusion in the star’s core exceeds the inward pull of its own gravity. This is called the Eddington limit. Beyond this limit, a star ought to push itself apart, or at least shed enough mass to reduce its internal energy generation to a lower, maintainable rate. In theory, a more massive star could not hold itself together, because of the mass loss resulting from the outflow of stellar material. In practice the theoretical Eddington Limit must be modified for high luminosity stars and the empirical Humphreys Davidson Limit is derived.
Astronomers have long theorized that as a protostar grows to a size beyond 120 M☉, something drastic must happen. Although the limit can be stretched for very early Population III stars, and the exact value is uncertain, if any stars still exist above 150-200 M☉, they would challenge current theories of stellar evolution. Studying the Arches cluster, which is the densest known cluster of stars in our galaxy, astronomers have confirmed that stars in that cluster do not occur any larger than about 150 M☉. One theory to explain rare ultramassive stars that exceed this limit, for example in the R136 star cluster, is the collision and merger of two massive stars in a close binary system.
See also 
- Luminous blue variable
- Wolf–Rayet star
- List of least massive stars
- List of largest known stars
- List of most luminous stars
- List of brightest stars
- Lists of stars
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