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Massive stars are few and far between.
This is a list of the most massive stars. The list is ordered by solar mass (1 solar mass = the mass of Earth's Sun).
Stellar mass is the most important attribute of a star. Combined with chemical compositions, mass determines a star’s luminosity, its physical size, and its ultimate fate. Due to their mass, most of the stars below will eventually go supernova or hypernova, and form black holes.
Massive stars uncertainties and caveats.
The masses listed in the table 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. An example is VV Cephei, which, depending on which property of the star is examined, could be between 25 to 40, or 100 solar masses.
Massive stars are rare. All the listed stars are many thousands of light years away, and that alone makes measurements difficult. In addition to being far away, it seems that most 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.
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 indeed consist of two or more companions in close orbit, each star being large in themselves, but not necessary massive; alternatively the system may still have one (or more) massive star, with much smaller companions.
Hence many of the masses listed below are contested, and being the subject of current research, are constantly being revised.
Amongst the most reliable listed masses are A1 and WR20a+b, which were obtained from orbital measurements. A1 and WR20a+b are both members of binary star systems (two stars orbiting around each other), 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 A1 and WR20a+b are both eclipsing binaries.
Massive stars stellar evolution.
A number of the stars may have started out with even greater masses than those currently estimated, but due to the huge amount of gas they outflow, and sub-supernova and supernova imposter explosion events, have lost many tens of solar masses of material.
Also there are a number of supernovae and hypernovae remnants whose pre-cursor stars' masses can be estimated based on pre-super/hypernova observations, the energy of the super/hypernova, and the type of super/hypernova event. These stars (if they had not exploded) would have easily made appearances in this list (however they are not shown below).
List of massive stars.
Known stars with an estimated mass of 25 or greater solar masses:
Massive stars and black holes.
Eddington's size limit of massive stars.
Astronomers have long theorized that as a protostar grows to a size beyond 120 solar masses, something drastic must happen. Although the limit can be stretched for very early Population III stars, if any stars existed above 120 solar mass, they would challenge current theories of stellar evolution.
The limit on mass arises because stars of greater mass have a higher rate of core energy generation, which is higher far out of proportion to their greater 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.
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