Stellar mass is a phrase that is used by astronomers to describe the
mass
Mass is an Intrinsic and extrinsic properties, intrinsic property of a physical body, body. It was traditionally believed to be related to the physical quantity, quantity of matter in a body, until the discovery of the atom and particle physi ...
of a
star
A star is a luminous spheroid of plasma (physics), plasma held together by Self-gravitation, self-gravity. The List of nearest stars and brown dwarfs, nearest star to Earth is the Sun. Many other stars are visible to the naked eye at night sk ...
. It is usually enumerated in terms of the
Sun's mass as a proportion of a
solar mass (). Hence, the bright star
Sirius has around .
A star's mass will vary over its lifetime as mass is lost with the
stellar wind or ejected via
pulsational behavior, or if additional mass is
accreted, such as from a
companion star.
Properties
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 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 (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 5–10 . These stars undergo
carbon fusion, with their lives ending in a core-collapse
supernova
A supernova (: supernovae or supernovas) is a powerful and luminous explosion of a star. A supernova occurs during the last stellar evolution, evolutionary stages of a massive star, or when a white dwarf is triggered into runaway nuclear fusion ...
explosion.
[ ]Black hole
A black hole is a massive, compact astronomical object so dense that its gravity prevents anything from escaping, even light. Albert Einstein's theory of general relativity predicts that a sufficiently compact mass will form a black hole. Th ...
s 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.
Range
One of the most massive stars known is Eta Carinae,[ with ; its lifespan is very short—only several million years at most. A study of the Arches Cluster suggests that is the upper limit for stars in the current era of the universe.][ A study has determined that stars larger than 150 in R136 were created through the collision and merger of massive stars in close binary systems, providing a way to sidestep the 150 limit.][LiveScience.com]
"Mystery of the 'Monster Stars' Solved: It Was a Monster Mash"
Natalie Wolchover, 7 August 2012
The first stars to form after the Big Bang may have been larger, up to 300 or more,[ due to the complete absence of elements heavier than ]lithium
Lithium (from , , ) is a chemical element; it has chemical symbol, symbol Li and atomic number 3. It is a soft, silvery-white alkali metal. Under standard temperature and pressure, standard conditions, it is the least dense metal and the ...
in their composition. This generation of supermassive, population III stars is long extinct, however, and currently only theoretical.
With a mass only 93 times that of Jupiter
Jupiter is the fifth planet from the Sun and the List of Solar System objects by size, largest in the Solar System. It is a gas giant with a Jupiter mass, mass more than 2.5 times that of all the other planets in the Solar System combined a ...
(), or .09 , AB Doradus C, a companion to AB Doradus A, is the smallest known star undergoing nuclear fusion in its core.[ For stars with similar metallicity to the Sun, the theoretical minimum mass the star can have, and still undergo fusion at the core, is estimated to be about 75 .][ Smaller bodies are called brown dwarfs, which occupy a poorly defined grey area between stars and ]gas giant
A gas giant is a giant planet composed mainly of hydrogen and helium. Jupiter and Saturn are the gas giants of the Solar System. The term "gas giant" was originally synonymous with "giant planet". However, in the 1990s, it became known that Uranu ...
s.
Change
The Sun is losing mass from the emission of electromagnetic energy and by the ejection of matter with the solar wind
The solar wind is a stream of charged particles released from the Sun's outermost atmospheric layer, the Stellar corona, corona. This Plasma (physics), plasma mostly consists of electrons, protons and alpha particles with kinetic energy betwee ...
. It is expelling about per year.[ The mass loss rate will increase when the Sun enters the red giant stage, climbing to y−1 when it reaches the tip of the red-giant branch. This will rise to y−1 on the asymptotic giant branch, before peaking at a rate of 10−5 to 10−4 y−1 as the Sun generates a planetary nebula. By the time the Sun becomes a degenerate ]white dwarf
A white dwarf is a Compact star, stellar core remnant composed mostly of electron-degenerate matter. A white dwarf is very density, dense: in an Earth sized volume, it packs a mass that is comparable to the Sun. No nuclear fusion takes place i ...
, it will have lost 46% of its starting mass.[
]
References
{{Star
Mass
Mass is an Intrinsic and extrinsic properties, intrinsic property of a physical body, body. It was traditionally believed to be related to the physical quantity, quantity of matter in a body, until the discovery of the atom and particle physi ...
Concepts in stellar astronomy
Mass