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 The Sun is the star at the centre of the Solar System. It is a massive, nearly perfect sphere of hot plasma, heated to incandescence by nuclear fusion reactions in its core, radiating the energy from its surface mainly as visible light a ...

's mass as a proportion of a

solar mass The solar mass () is a frequently used unit of mass in astronomy, equal to approximately . It is approximately equal to the mass of the Sun. It is often used to indicate the masses of other stars, as well as stellar clusters, nebulae, galaxie ...

(). Hence, the bright star

Sirius Sirius is the brightest star in the night sky. Its name is derived from the Greek word (Latin script: ), meaning 'glowing' or 'scorching'. The star is designated Canis Majoris, Latinized to Alpha Canis Majoris, and abbr ...

has around . A star's mass will vary over its lifetime as mass is lost with the

stellar wind A stellar wind is a flow of gas ejected from the stellar atmosphere, upper atmosphere of a star. It is distinguished from the bipolar outflows characteristic of young stars by being less collimated, although stellar winds are not generally spheri ...

or ejected via pulsational behavior, or if additional mass is accreted, such as from a

companion star A binary star or binary star system is a system of two stars that are gravitationally bound to and in orbit around each other. Binary stars in the night sky that are seen as a single object to the naked eye are often resolved as separate stars us ...

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 The asymptotic giant branch (AGB) is a region of the Hertzsprung–Russell diagram populated by evolved cool luminous stars. This is a period of stellar evolution undertaken by all low- to intermediate-mass stars (about 0.5 to 8 solar masses) lat ...

(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 In physical cosmology, the age of the universe is the cosmological time, time elapsed since the Big Bang: 13.79 billion years. Astronomers have two different approaches to determine the age of the universe. One is based on a particle physics ...

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 The triple-alpha process is a set of nuclear fusion reactions by which three helium-4 nuclei (alpha particles) are transformed into carbon. In stars Helium accumulates in the cores of stars as a result of the proton–proton chain reaction a ...

and develop a degenerate carbon–oxygen core. ''Massive stars'' have a minimum mass of 5–10 . These stars undergo

carbon fusion The carbon-burning process or carbon fusion is a set of nuclear fusion reactions that take place in the cores of massive stars (at least 4 \beginM_\odot\end at birth) that combines carbon into other elements. It requires high temperatures (> 5&t ...

, 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 The surface gravity, ''g'', of an astronomical object is the gravitational acceleration experienced at its surface at the equator, including the effects of rotation. The surface gravity may be thought of as the acceleration due to gravity experi ...

. Giant stars have a much lower surface gravity than

main sequence stars In astronomy, the main sequence is a classification of stars which appear on plots of stellar color versus brightness as a continuous and distinctive band. Stars on this band are known as main-sequence stars or dwarf stars, and positions of star ...

, 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 line Absorption spectroscopy is spectroscopy that involves techniques that measure the absorption (electromagnetic radiation), absorption of electromagnetic radiation, as a function of frequency or wavelength, due to its interaction with a sample. Th ...

Range

One of the most massive stars known is

Eta Carinae η Carinae (Eta Carinae, abbreviated to η Car), formerly known as η Argus, is a stellar system containing at least two stars with a combined luminosity greater than five million times that of the Sun, located around ...

, with ; its lifespan is very short—only several million years at most. A study of the

Arches Cluster The Arches Cluster is the densest known star cluster in the Milky Way, about 100 light-years from Galactic Center, its center in the constellation Sagittarius (constellation), Sagittarius (The Archer), 25,000 light-years from Earth. Its discovery ...

suggests that is the upper limit for stars in the current era of the universe. The reason for this limit is not precisely known, but it is partially due to the

Eddington luminosity The Eddington luminosity, also referred to as the Eddington limit, is the maximum luminosity a body (such as a star) can achieve when there is balance between the force of radiation acting outward and the gravitational force acting inward. The stat ...

which defines the maximum amount of luminosity that can pass through the atmosphere of a star without ejecting the gases into space. However, a star named

R136a1 R136a1 (short for RMC 136a1) is one of the List of most massive stars, most massive and list of most luminous stars, luminous stars known, at nearly and nearly 4.7 million , and is also one of the List of hottest stars, hottest, at around ...

in the RMC 136a star cluster has been measured at 215 , putting this limit into question. A study has determined that stars larger than 150 in

R136 R136 (formerly known as RMC 136 from the Radcliffe Observatory Magellanic Clouds catalogue) is the central concentration of stars in the NGC 2070 star cluster, which lies at the centre of the Tarantula Nebula in the Large Magellanic Cloud. W ...

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 In 1944, Walter Baade categorized groups of stars within the Milky Way into stellar populations. In the abstract of the article by Baade, he recognizes that Jan Oort originally conceived this type of classification in 1926. Baade observed tha ...

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 . When the metallicity is very low, however, a recent study of the faintest stars found that the minimum star size seems to be about 8.3% of the solar mass, or about 87 . Smaller bodies are called

brown dwarf Brown dwarfs are substellar objects that have more mass than the biggest gas giant planets, but less than the least massive main sequence, main-sequence stars. Their mass is approximately 13 to 80 Jupiter mass, times that of Jupiter ()not big en ...

s, 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 ...

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 A red giant is a luminous giant star of low or intermediate mass (roughly 0.3–8 solar masses ()) in a late phase of stellar evolution. The stellar atmosphere, outer atmosphere is inflated and tenuous, making the radius large and the surface t ...

stage, climbing to y⁻¹ when it reaches the

tip of the red-giant branch Tip of the red-giant branch (TRGB) is a primary distance indicator used in astronomy. It uses the luminosity of the brightest red-giant-branch stars in a galaxy as a standard candle to gauge the distance to that galaxy. It has been used in conjun ...

. This will rise to y⁻¹ on the

, before peaking at a rate of 10⁻⁵ to 10⁻⁴ y⁻¹ as the Sun generates a

planetary nebula A planetary nebula is a type of emission nebula consisting of an expanding, glowing shell of ionized gas ejected from red giant stars late in their lives. The term "planetary nebula" is a misnomer because they are unrelated to planets. The ...

. 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

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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