List of most massive stars

Indeed, many of the masses listed in the table below are inferred from theory, using difficult measurements of the stars' temperatures, composition, and absolute brightnesses.

All the masses listed below are uncertain: Both the theory and the measurements are pushing the limits of current knowledge and technology.

In addition to being far away, many stars of such extreme mass are surrounded by clouds of outflowing gas created by extremely powerful stellar winds; the surrounding gas interferes with the already difficult-to-obtain measurements of stellar temperatures and brightnesses, which greatly complicates the issue of estimating internal chemical compositions and structures.

This mass may have been expelled by superwinds: high velocity winds that are driven by the hot photosphere into interstellar space.

The process forms an enlarged extended envelope around the star that interacts with the nearby interstellar medium and infuses the adjacent volume of space with elements heavier than hydrogen or helium.

The Eddington limit is the point beyond which a star ought to push itself apart, or at least shed enough mass to reduce its internal energy generation to a lower, maintainable rate.

Before their demise, the hypothetical metal-free Population III stars would have had the highest allowed mass, somewhere around 300 M☉.

In theory, a more massive star could not hold itself together because of the mass loss resulting from the outflow of stellar material.

Stars that are at least sometimes visible to the unaided eye have their apparent magnitude (6.5 or brighter) highlighted in blue.

[A] Technically they are not stars, as they no longer generate heat and light via nuclear fusion in their cores.