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The term
dwarf star refers to a variety of distinct classes of
starA star is a massive, luminous sphere of plasma held together by gravity. At the end of its lifetime, a star can also contain a proportion of degenerate matter. The nearest star to Earth is the Sun, which is the source of most of the energy on Earth...
s.
- Dwarf star alone generally refers to any main sequence
The main sequence is a continuous and distinctive band of stars that appears on plots of stellar color versus brightness. These color-magnitude plots are known as Hertzsprung–Russell diagrams after their co-developers, Ejnar Hertzsprung and Henry Norris Russell...
star, a star of luminosity class V.
- Red dwarf
According to the Hertzsprung-Russell diagram, a red dwarf star is a small and relatively cool star, of the main sequence, either late K or M spectral type....
s are low-mass main sequence stars.
- Yellow dwarf
A G-type main-sequence star , often called a yellow dwarf, is a main-sequence star of spectral type G and luminosity class V. Such a star has about 0.8 to 1.2 solar masses and surface temperature of between 5,300 and 6,000 K., Tables VII, VIII...
s are main sequence (dwarf) stars with masses comparable to that of the SunThe Sun is the star at the center of the Solar System. It is almost perfectly spherical and consists of hot plasma interwoven with magnetic fields...
. The Sun is a yellow dwarf.
- A blue dwarf
A blue dwarf is a hypothetical class of star that develops from a red dwarf star after it has exhausted much of its hydrogen fuel supply. Since red dwarf stars fuse their hydrogen slowly and are fully convective , the universe is currently not old enough for any blue dwarfs to have formed yet...
is a low-mass star which is hypothesized to be the post-main sequence form of a red dwarf.
- A white dwarf
A white dwarf, also called a degenerate dwarf, is a small star composed mostly of electron-degenerate matter. They are very dense; a white dwarf's mass is comparable to that of the Sun and its volume is comparable to that of the Earth. Its faint luminosity comes from the emission of stored...
is a star composed of electron-degenerate matter, thought to be the final stage in the evolution of stars not massive enough to undergo a Type II supernovaA Type II supernova results from the rapid collapse and violent explosion of a massive star. A star must have at least 9 times, and no more than 40–50 times the mass of the Sun for this type of explosion. It is distinguished from other types of supernova by the presence of hydrogen in its spectrum...
—stars less massive than roughly 9 solar massThe solar mass , , is a standard unit of mass in astronomy, used to indicate the masses of other stars and galaxies...
es.
- A black dwarf
A black dwarf is a hypothetical stellar remnant, created when a white dwarf becomes sufficiently cool to no longer emit significant heat or light...
refers to a white dwarf that has cooled sufficiently such that it no longer emits any visible light.
- A brown dwarf
Brown dwarfs are sub-stellar objects which are too low in mass to sustain hydrogen-1 fusion reactions in their cores, which is characteristic of stars on the main sequence. Brown dwarfs have fully convective surfaces and interiors, with no chemical differentiation by depth...
is a sub-stellar object not massive enough to ever fuse hydrogenHydrogen is the chemical element with atomic number 1. It is represented by the symbol H. With an average atomic weight of , hydrogen is the lightest and most abundant chemical element, constituting roughly 75% of the Universe's chemical elemental mass. Stars in the main sequence are mainly...
into heliumHelium is the chemical element with atomic number 2 and an atomic weight of 4.002602, which is represented by the symbol He. It is a colorless, odorless, tasteless, non-toxic, inert, monatomic gas that heads the noble gas group in the periodic table...
—less than about 0.08 solar masses.