Red dwarf

redred dwarf starsred dwarfsMM-dwarf starred sunM dwarfsM-dwarfM-type dwarfM-type main-sequence star
A red dwarf (or M dwarf) is a small and cool star on the main sequence, of M spectral type.wikipedia
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Proxima Centauri

Alpha Proximaits host starProxima
Proxima Centauri, the nearest star to the Sun, is a red dwarf (Type M5, apparent magnitude 11.05), as are fifty of the sixty nearest stars.
Proxima Centauri, or Alpha Centauri C, is a red dwarf, a small low-mass star, about 4.244 ly from the Sun in the constellation of Centaurus.

List of nearest stars and brown dwarfs

passing starsnearest starsclosest stars
Proxima Centauri, the nearest star to the Sun, is a red dwarf (Type M5, apparent magnitude 11.05), as are fifty of the sixty nearest stars.
These systems contain a total of 63 stars, of which 50 are red dwarfs, by far the most common type of star in the Milky Way.

K-type main-sequence star

orange dwarfKK-type star
Sometimes K-type main-sequence stars, with masses between 0.50-0.8 solar mass, are also included.
A K-type main-sequence star (K V), also referred to as an K dwarf, is a main-sequence (hydrogen-burning) star of spectral type K and luminosity class V. These stars are intermediate in size between red M-type main-sequence stars ("red dwarfs") and yellow G-type main-sequence stars.

Sun

solarSolThe Sun
Red dwarfs are by far the most common type of star in the Milky Way, at least in the neighborhood of the Sun, but because of their low luminosity, individual red dwarfs cannot be easily observed.
The Sun has an absolute magnitude of +4.83, estimated to be brighter than about 85% of the stars in the Milky Way, most of which are red dwarfs.

Brown dwarf

brown dwarfsbrown dwarvesPlanetar
The coolest true main-sequence stars are thought to have spectral types around L2 or L3, but many objects cooler than about M6 or M7 are brown dwarfs, insufficiently massive to sustain hydrogen-1 fusion.
Brown dwarfs are substellar objects that occupy the mass range between the heaviest gas giant planets and the lightest stars, having masses between approximately 13 to 75–80 times that of Jupiter, or approximately 2.5 kg to about 1.5 kg. Below this range are the sub-brown dwarfs (sometimes referred to as rogue planets), and above it are the lightest red dwarfs (M9 V).

Stellar classification

spectral typeK-typeG-type
A red dwarf (or M dwarf) is a small and cool star on the main sequence, of M spectral type.
Red dwarfs are a deep shade of orange, and brown dwarfs do not literally appear brown, but hypothetically would appear dim grey to a nearby observer.

Milky Way

galaxyMilky Way Galaxyour galaxy
Red dwarfs are by far the most common type of star in the Milky Way, at least in the neighborhood of the Sun, but because of their low luminosity, individual red dwarfs cannot be easily observed. This provides a lower limit to the age of the Universe and also allows formation timescales to be placed upon the structures within the Milky Way, such as the Galactic halo and Galactic disk.
On November 4, 2013, astronomers reported, based on Kepler space mission data, that there could be as many as 40 billion Earth-sized planets orbiting in the habitable zones of Sun-like stars and red dwarfs within the Milky Way.

Lacaille 8760

Even the largest red dwarfs (for example HD 179930, HIP 12961 and Lacaille 8760) have only about 10% of the Sun's luminosity.
Lacaille 8760 (AX Microscopii) is a red dwarf star in the constellation Microscopium.

HIP 12961

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Even the largest red dwarfs (for example HD 179930, HIP 12961 and Lacaille 8760) have only about 10% of the Sun's luminosity.
HIP 12961 is a dim red dwarf star located approximately 75 light-years away in the constellation of Eridanus.

Main sequence

main-sequencemain sequence dwarfmain-sequence star
A red dwarf (or M dwarf) is a small and cool star on the main sequence, of M spectral type.
For the cooler stars, dwarfs such as red dwarfs, orange dwarfs, and yellow dwarfs are indeed much smaller and dimmer than other stars of those colors.

Thermonuclear fusion

thermonuclearfusingfusion
Hence the helium produced by the thermonuclear fusion of hydrogen is constantly remixed throughout the star, avoiding helium buildup at the core, thereby prolonging the period of fusion.
The mass needed, however, is so great that gravitational confinement is only found in stars—the least massive stars capable of sustained fusion are red dwarfs, while brown dwarfs are able to fuse deuterium and lithium if they are of sufficient mass. In stars heavy enough, after the supply of hydrogen is exhausted in their cores, their cores (or a shell around the core) start fusing helium to carbon.

Barnard's Star

Barnard’s Starextrasolar planets
It has been calculated that a red dwarf (approximately the mass of the nearby Barnard's Star) would stay on the main sequence for 2.5 trillion years, followed by five billion years as a blue dwarf, during which the star would have one third of the Sun's luminosity and a surface temperature of 6,500–8,500 kelvins.
Barnard's Star is a very-low-mass red dwarf about 6 light-years away from Earth in the constellation of Ophiuchus.

Blue dwarf (red-dwarf stage)

blue dwarfblue dwarfsblue
According to computer simulations, the minimum mass a red dwarf must have in order to eventually evolve into a red giant is ; less massive objects, as they age, would increase their surface temperatures and luminosities becoming blue dwarfs and finally white dwarfs.
A blue dwarf is a predicted class of star that develops from a red dwarf after it has exhausted much of its hydrogen fuel supply.

White dwarf

white dwarfswhite dwarf starcentral star
According to computer simulations, the minimum mass a red dwarf must have in order to eventually evolve into a red giant is ; less massive objects, as they age, would increase their surface temperatures and luminosities becoming blue dwarfs and finally white dwarfs.
The first white dwarf discovered was in the triple star system of 40 Eridani, which contains the relatively bright main sequence star 40 Eridani A, orbited at a distance by the closer binary system of the white dwarf 40 Eridani B and the main sequence red dwarf 40 Eridani C.

Lalande 21185

22 H Camelopardalis
and HD 95735/Lalande 21185 (M2 V). While HD 147379 was not considered a standard by expert classifiers in later compendia of standards, Lalande 21185 is still a primary standard for M2 V. Robert Garrison does not list any "anchor" standards among the red dwarfs, but Lalande 21185 has survived as a M2 V standard through many compendia. The M-dwarf primary spectral standards are: GJ 270 (M0 V), GJ 229A (M1 V), Lalande 21185 (M2 V), Gliese 581 (M3 V), Gliese 402 (M4 V), GJ 51 (M5 V), Wolf 359 (M6 V), Van Biesbroeck 8 (M7 V), VB 10 (M8 V), LHS 2924 (M9 V).
Lalande 21185 is a star in the constellation of Ursa Major, relevant for being the brightest red dwarf observable in the northern hemisphere (only AX Microscopii and Lacaille 9352, in the southern hemisphere, are brighter).

Gliese 229

Gliese 229B
The M-dwarf primary spectral standards are: GJ 270 (M0 V), GJ 229A (M1 V), Lalande 21185 (M2 V), Gliese 581 (M3 V), Gliese 402 (M4 V), GJ 51 (M5 V), Wolf 359 (M6 V), Van Biesbroeck 8 (M7 V), VB 10 (M8 V), LHS 2924 (M9 V).
Gliese 229 (also written as Gl 229 or GJ 229) is a red dwarf about 19 light years away in the constellation Lepus.

Gliese 581

Gliese planetary system
The M-dwarf primary spectral standards are: GJ 270 (M0 V), GJ 229A (M1 V), Lalande 21185 (M2 V), Gliese 581 (M3 V), Gliese 402 (M4 V), GJ 51 (M5 V), Wolf 359 (M6 V), Van Biesbroeck 8 (M7 V), VB 10 (M8 V), LHS 2924 (M9 V).
Gliese 581 is a star of spectral type M3V (a red dwarf) at the center of the Gliese 581 planetary system, about 20 light years away from Earth in the Libra constellation.

Wolf 359

star of the same name
The M-dwarf primary spectral standards are: GJ 270 (M0 V), GJ 229A (M1 V), Lalande 21185 (M2 V), Gliese 581 (M3 V), Gliese 402 (M4 V), GJ 51 (M5 V), Wolf 359 (M6 V), Van Biesbroeck 8 (M7 V), VB 10 (M8 V), LHS 2924 (M9 V).
Wolf 359 is a red dwarf star located in the constellation Leo, near the ecliptic.

Convection zone

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Stellar models indicate that red dwarfs less than are fully convective.
This combination of circumstances produces an outer convection zone, the top of which is visible in the Sun as solar granulation. Low mass main sequences of stars, such as red dwarfs below 0.35 solar masses, as well as pre-main sequence stars on the Hayashi track, are convective throughout and do not contain a radiation zone.

VB 10

Van Biesbroeck's starbGliese (GJ) 752B
The M-dwarf primary spectral standards are: GJ 270 (M0 V), GJ 229A (M1 V), Lalande 21185 (M2 V), Gliese 581 (M3 V), Gliese 402 (M4 V), GJ 51 (M5 V), Wolf 359 (M6 V), Van Biesbroeck 8 (M7 V), VB 10 (M8 V), LHS 2924 (M9 V).
VB 10 or Van Biesbroeck's star is a very small and very dim red dwarf located in the constellation Aquila.

Exoplanet

extrasolar planetexoplanetsplanet
Many red dwarfs are orbited by exoplanets, but large Jupiter-sized planets are comparatively rare.
Assuming there are 200 billion stars in the Milky Way, it can be hypothesized that there are 11 billion potentially habitable Earth-sized planets in the Milky Way, rising to 40 billion if planets orbiting the numerous red dwarfs are included.

V1054 Ophiuchi

The M-dwarf primary spectral standards are: GJ 270 (M0 V), GJ 229A (M1 V), Lalande 21185 (M2 V), Gliese 581 (M3 V), Gliese 402 (M4 V), GJ 51 (M5 V), Wolf 359 (M6 V), Van Biesbroeck 8 (M7 V), VB 10 (M8 V), LHS 2924 (M9 V).
It consists of five stars, all of which are red dwarfs.

Gravitational microlensing

microlensingmicrolensing eventdetected by microlensing
On the other hand, microlensing surveys indicate that long-orbital-period Neptune-mass planets are found around one in three red dwarfs.
It is thus an ideal technique to study the galactic population of such faint or dark objects as brown dwarfs, red dwarfs, planets, white dwarfs, neutron stars, black holes, and

Spiral galaxy

spiral galaxiesspiral armspiral
This provides a lower limit to the age of the Universe and also allows formation timescales to be placed upon the structures within the Milky Way, such as the Galactic halo and Galactic disk.
The motion of halo stars does bring them through the disc on occasion, and a number of small red dwarfs close to the Sun are thought to belong to the galactic halo, for example Kapteyn's Star and Groombridge 1830.

Jupiter

Jovianplanet JupiterGiove
Many red dwarfs are orbited by exoplanets, but large Jupiter-sized planets are comparatively rare.
Although Jupiter would need to be about 75 times as massive to fuse hydrogen and become a star, the smallest red dwarf is only about 30 percent larger in radius than Jupiter.