Stellar mass

Stellar mass is a phrase that is used by astronomers to describe the mass of a star. It is usually enumerated in terms of the Sun's mass as a proportion of a solar mass (M_☉). Hence, the bright star Sirius has around 2.02 M_☉. A star's mass will vary over its lifetime as additional mass becomes accreted, such as from a companion star, or mass is ejected with the stellar wind or pulsational behavior.

Stars are sometimes grouped by mass based upon their evolutionary behavior as they approach the end of their nuclear fusion lifetimes.

Very low mass stars with masses below 0.5 M_☉ do not enter the asymptotic giant branch (AGB) but evolve directly into white dwarfs. (At least in theory; the lifetimes of such stars are long enough -- longer than the age of the universe to date -- that none has yet had time to evolve to this point and be observed.)

Low mass stars with a mass below about 1.8–2.2 M_☉ (depending on composition) do enter the AGB, where they develop a degenerate helium core.

Intermediate-mass stars undergo helium fusion and develop a degenerate carbon-oxygen core.

Massive stars have a minimum mass of 7–10 M_☉, but this may be as low as 5–6 M_☉. These stars undergo carbon fusion, with their lives ending in a core-collapse supernova explosion.Black holes created as a result of a stellar collapse are termed stellar mass black holes.

The combination of the radius and the mass of a star determines the surface gravity. Giant stars have a much lower surface gravity than main sequence stars, while the opposite is the case for degenerate, compact stars such as white dwarfs. The surface gravity can influence the appearance of a star's spectrum, with higher gravity causing a broadening of the absorption lines.

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