--- title: Red dwarf summary: A small, cool, faint main-sequence star of spectral class M, between about 8% and 60% of the Sun's mass. Red dwarfs are about three quarters of all stars, live for trillions of years, flare violently when young, and host many of the nearest known rocky planets. science_status: [observed, sim] categories: [Stars, Main-sequence stars, M-type stars] aliases: [Red dwarfs, M dwarf, M dwarfs, M-type main-sequence star, M-dwarf, Red dwarf star, RDW, dM, Flare star] infobox: type: star_class name: Red dwarf image: File:Proxima_Centauri_Hubble_potw1343a.jpg caption: "Observation: Proxima Centauri, the nearest star to the Sun, imaged by the Hubble Space Telescope. Credit: ESA/Hubble & NASA" code: RDW stellar_class_key: red_dwarf spectral_types_covered: "M0V to M9.5V" luminosity_class: V effective_temperature: {value: "about 2,350 to 3,900 (M0V 3,850; M5V 3,060; M9V 2,380)", unit: K, source: observed} mass: {value: "about 0.08 to 0.6 (M0V 0.57; M5V 0.162; M9V 0.079)", unit: M_Sun, source: observed} radius: {value: "about 0.10 to 0.6 (M0V 0.59; M5V 0.196; M9V 0.102)", unit: R_Sun, source: observed} luminosity: {value: "about 0.0003 to 0.07", unit: L_Sun, source: observed} main_sequence_lifetime: {value: "hundreds of billions to about 10 trillion years", unit: yr, source: model} bv_colour: {value: "1.42 (M0V) to 2.17 (M9V)", unit: mag, source: observed} absolute_magnitude_v: {value: "8.8 (M0V) to 19.4 (M9V)", unit: mag, source: observed} perceived_colour: "Orange rather than red to the eye; none is bright enough to see without a telescope" activity: "Strong magnetic activity and frequent flares, especially when young; fully convective below about 0.35 M_Sun" share_of_stars: "About 74% of stars within 10 pc (249 of 337)" habitable_zone: {value: "M0V about 0.27 to 0.52; M5V about 0.06 to 0.11 (conservative, Kopparapu et al. 2014)", unit: AU, source: model} planet_occurrence: "Small planets common; Proxima Centauri, Barnard's Star and TRAPPIST-1 all host rocky planets" subtypes: "RDW-EM early, RDW-MM mid, RDW-LM late, each quiet (QT) or active (AC); RDW-UC ultracool (sim codes)" real_examples: "Proxima Centauri (M5.5Ve), Barnard's Star (M4V), TRAPPIST-1 (M7.5 to M8V)" physics_engine: "Red dwarf physics engine and subtype classifier" science_doc: "The sim's red dwarf science and flare-environment references" last_verified: "2026-09-27, writer B" sim: entity: stellar_class.red_dwarf refs: - id: eem22 type: dataset author: [{family: Mamajek, given: Eric E.}] title: "A Modern Mean Dwarf Stellar Color and Effective Temperature Sequence (version 2022.04.16)" URL: https://www.pas.rochester.edu/~emamajek/EEM_dwarf_UBVIJHK_colors_Teff.txt accessed: 2026-09-27 - id: pm13 type: article-journal author: [{family: Pecaut, given: Mark J.}, {family: Mamajek, given: Eric E.}] title: "Intrinsic Colors, Temperatures, and Bolometric Corrections of Pre-main-sequence Stars" container-title: The Astrophysical Journal Supplement Series volume: 208 page: 9 issued: 2013 DOI: 10.1088/0067-0049/208/1/9 - id: reyle21 type: article-journal author: [{family: Reylé, given: C.}, {family: Jardine, given: K.}, {family: Fouqué, given: P.}, {literal: "et al."}] title: "The 10 parsec sample in the Gaia era" container-title: Astronomy & Astrophysics volume: 650 page: A201 issued: 2021 DOI: 10.1051/0004-6361/202140985 - id: cb97 type: article-journal author: [{family: Chabrier, given: G.}, {family: Baraffe, given: I.}] title: "Structure and evolution of low-mass stars" container-title: Astronomy & Astrophysics volume: 327 page: 1039-1053 issued: 1997 URL: https://arxiv.org/abs/astro-ph/9704118 - id: jao18 type: article-journal author: [{family: Jao, given: Wei-Chun}, {family: Henry, given: Todd J.}, {family: Gies, given: Douglas R.}, {family: Hambly, given: Nigel C.}] title: "A Gap in the Lower Main Sequence Revealed by Gaia Data Release 2" container-title: The Astrophysical Journal Letters volume: 861 page: L11 issued: 2018 DOI: 10.3847/2041-8213/aacdf6 - id: lba97 type: article-journal author: [{family: Laughlin, given: Gregory}, {family: Bodenheimer, given: Peter}, {family: Adams, given: Fred C.}] title: "The End of the Main Sequence" container-title: The Astrophysical Journal volume: 482 page: 420-432 issued: 1997 DOI: 10.1086/304125 - id: al97 type: article-journal author: [{family: Adams, given: Fred C.}, {family: Laughlin, given: Gregory}] title: "A dying universe: the long-term fate and evolution of astrophysical objects" container-title: Reviews of Modern Physics volume: 69 page: 337-372 issued: 1997 DOI: 10.1103/RevModPhys.69.337 - id: kervella17 type: article-journal author: [{family: Kervella, given: P.}, {family: Thévenin, given: F.}, {family: Lovis, given: C.}] title: "Proxima's orbit around alpha Centauri" container-title: Astronomy & Astrophysics volume: 598 page: L7 issued: 2017 DOI: 10.1051/0004-6361/201629930 - id: anglada16 type: article-journal author: [{family: Anglada-Escudé, given: Guillem}, {family: Amado, given: Pedro J.}, {family: Barnes, given: John}, {literal: "et al."}] title: "A terrestrial planet candidate in a temperate orbit around Proxima Centauri" container-title: Nature volume: 536 page: 437-440 issued: 2016 DOI: 10.1038/nature19106 - id: faria22 type: article-journal author: [{family: Faria, given: J. P.}, {family: Suárez Mascareño, given: A.}, {family: Figueira, given: P.}, {literal: "et al."}] title: "A candidate short-period sub-Earth orbiting Proxima Centauri" container-title: Astronomy & Astrophysics volume: 658 page: A115 issued: 2022 DOI: 10.1051/0004-6361/202142337 - id: howard18 type: article-journal author: [{family: Howard, given: Ward S.}, {family: Tilley, given: Matt A.}, {family: Corbett, given: Hank}, {literal: "et al."}] title: "The First Naked-eye Superflare Detected from Proxima Centauri" container-title: The Astrophysical Journal Letters volume: 860 page: L30 issued: 2018 DOI: 10.3847/2041-8213/aacaf3 - id: macgregor21 type: article-journal author: [{family: MacGregor, given: Meredith A.}, {family: Weinberger, given: Alycia J.}, {family: Loyd, given: R. O. Parke}, {literal: "et al."}] title: "Discovery of an Extremely Short Duration Flare from Proxima Centauri Using Millimeter through Far-ultraviolet Observations" container-title: The Astrophysical Journal Letters volume: 911 page: L25 issued: 2021 DOI: 10.3847/2041-8213/abf14c - id: crowley24 type: article-journal author: [{family: Crowley, given: James}, {family: Wheatland, given: Michael S.}, {family: Yang, given: Kai}] title: "Superflare rate variability on M dwarfs" container-title: Monthly Notices of the Royal Astronomical Society volume: 530 page: 457-472 issued: 2024 DOI: 10.1093/mnras/stae818 - id: gh24 type: article-journal author: [{family: González Hernández, given: J. I.}, {family: Suárez Mascareño, given: A.}, {family: Silva, given: A. M.}, {literal: "et al."}] title: "A sub-Earth-mass planet orbiting Barnard's star" container-title: Astronomy & Astrophysics volume: 690 page: A79 issued: 2024 DOI: 10.1051/0004-6361/202451311 - id: basant25 type: article-journal author: [{family: Basant, given: Ritvik}, {family: Luque, given: Rafael}, {family: Bean, given: Jacob L.}, {literal: "et al."}] title: "Four Sub-Earth Planets Orbiting Barnard's Star from MAROON-X and ESPRESSO" container-title: The Astrophysical Journal Letters volume: 982 page: L1 issued: 2025 DOI: 10.3847/2041-8213/adb8d5 - id: ribas18 type: article-journal author: [{family: Ribas, given: I.}, {family: Tuomi, given: M.}, {family: Reiners, given: A.}, {literal: "et al."}] title: "A candidate super-Earth planet orbiting near the snow line of Barnard's star" container-title: Nature volume: 563 page: 365-368 issued: 2018 DOI: 10.1038/s41586-018-0677-y - id: gillon17 type: article-journal author: [{family: Gillon, given: Michaël}, {family: Triaud, given: Amaury H. M. J.}, {family: Demory, given: Brice-Olivier}, {literal: "et al."}] title: "Seven temperate terrestrial planets around the nearby ultracool dwarf star TRAPPIST-1" container-title: Nature volume: 542 page: 456-460 issued: 2017 DOI: 10.1038/nature21360 - id: agol21 type: article-journal author: [{family: Agol, given: Eric}, {family: Dorn, given: Caroline}, {family: Grimm, given: Simon L.}, {literal: "et al."}] title: "Refining the Transit-timing and Photometric Analysis of TRAPPIST-1: Masses, Radii, Densities, Dynamics, and Ephemerides" container-title: The Planetary Science Journal volume: 2 page: 1 issued: 2021 DOI: 10.3847/PSJ/abd022 - id: zieba23 type: article-journal author: [{family: Zieba, given: Sebastian}, {family: Kreidberg, given: Laura}, {family: Ducrot, given: Elsa}, {literal: "et al."}] title: "No thick carbon dioxide atmosphere on the rocky exoplanet TRAPPIST-1 c" container-title: Nature volume: 620 page: 746-749 issued: 2023 DOI: 10.1038/s41586-023-06232-z - id: glidden25 type: article-journal author: [{family: Glidden, given: Ana}, {family: Ranjan, given: Sukrit}, {family: Seager, given: Sara}, {literal: "et al."}] title: "JWST-TST DREAMS: Secondary Atmosphere Constraints for the Habitable Zone Planet TRAPPIST-1 e" container-title: The Astrophysical Journal Letters volume: 990 page: L53 issued: 2025 DOI: 10.3847/2041-8213/adf62e - id: hh21 type: article-journal author: [{family: Harre, given: Jan-Vincent}, {family: Heller, given: René}] title: "Digital color codes of stars" container-title: Astronomische Nachrichten volume: 342 page: 578-587 issued: 2021 DOI: 10.1002/asna.202113868 - id: kopparapu2014 type: article-journal author: [{family: Kopparapu, given: Ravi Kumar}, {family: Ramirez, given: Ramses M.}, {family: SchottelKotte, given: James}, {literal: "et al."}] title: "Habitable Zones around Main-sequence Stars: Dependence on Planetary Mass" container-title: The Astrophysical Journal Letters volume: 787 page: L29 issued: 2014 DOI: 10.1088/2041-8205/787/2/L29 images_wanted: - file: File:Proxima_Centauri_Hubble_potw1343a.jpg subject: "Proxima Centauri as a bright point with diffraction spikes among fainter stars, imaged by Hubble" source: esa-hubble page_url: https://esahubble.org/images/potw1343a/ credit: "ESA/Hubble & NASA" licence: "CC BY 4.0 (ESA/Hubble usage terms)" - file: File:Barnards_Star_planet_ESO_eso2414a.jpg subject: "Artist's impression of a small rocky planet close to the red dwarf Barnard's Star" source: eso page_url: https://www.eso.org/public/images/eso2414a/ credit: "ESO/M. Kornmesser" licence: "CC BY 4.0 (ESO usage terms)" - file: File:TRAPPIST-1_system_PIA21751.jpg subject: "Artist's concept of the seven rocky planets of TRAPPIST-1 and their small red star" source: nasa page_url: https://science.nasa.gov/photojournal/trappist-1-system-artist-concept/ credit: "NASA/JPL-Caltech" licence: "Public domain (NASA)" --- A **red dwarf** is a small, cool star on the main sequence, fusing hydrogen in its core like the Sun but at a far slower rate. Red dwarfs are the stars of spectral class M, with between about 8% and 60% of the Sun's mass, surface temperatures of about 2,300 to 3,900 K, and luminosities from about 7% of the Sun's down to a few ten-thousandths :cite[eem22]. They are the commonest stars in the Galaxy, about three in every four :cite[reyle21], yet not one is bright enough to see with the naked eye. They will also be the last stars shining: the smallest will burn for around ten trillion years :cite[lba97]. ## Characteristics ### Small, cool and faint Along the M sequence, size, temperature and brightness all fall with mass :cite[eem22] :cite[pm13]: | Type | Temperature (K) | Mass (Sun = 1) | Radius (Sun = 1) | Luminosity (Sun = 1) | |---|---|---|---|---| | M0V | 3,850 | 0.57 | 0.59 | 0.069 | | M5V | 3,060 | 0.162 | 0.196 | 0.0030 | | M9V | 2,380 | 0.079 | 0.102 | 0.0003 | The lightest red dwarfs are barely larger than Jupiter. Below about 0.075 solar masses an object cannot sustain hydrogen fusion and is a [[Brown dwarf|brown dwarf]]. Despite the name, red dwarfs do not look red: models of how their light appears to the human eye show a warm orange, paler than a blackbody of the same temperature would suggest :cite[hh21]. ### Stirred from top to bottom Red dwarfs below about 0.35 solar masses are convective all the way through: hot gas rises from the core to the surface and cool gas sinks, whatever the star's metal content :cite[cb97]. Heavier ones have a radiative core, like the Sun. The change leaves a mark in the Gaia data: a narrow gap in the main sequence near spectral type M3V, where stars pass from one structure to the other :cite[jao18]. Full convection mixes fresh hydrogen into the core throughout the star's life, which is one reason red dwarfs last so long. ### Flares Convection and rotation together wind up strong magnetic fields, and red dwarfs, particularly young and fast-rotating ones, release that magnetic energy in flares far more powerful, relative to the star, than the Sun's. In March 2016 the Evryscope survey caught Proxima Centauri brightening 68-fold in a flare that briefly made it visible to the naked eye, releasing about 10³³·⁵ ergs :cite[howard18]. On 1 May 2019 the Hubble Space Telescope and the ALMA radio array together recorded a Proxima flare that brightened the star more than 14,000 times in far-ultraviolet light in a few seconds :cite[macgregor21]. Flare rates are not steady: a TESS study of 658 late-K and M dwarfs found 66 whose superflare rate changed over time :cite[crowley24]. For any planets close in, that radiation and the particles that come with it are a hazard for atmospheres and for life. ### Lives of trillions of years A star's main-sequence life is roughly its fuel divided by its burn rate, and red dwarfs have little fuel but burn it very slowly. The lightest hydrogen-burning stars will last about 10¹³ years, some 700 times the present age of the universe :cite[lba97]. Stars below about 0.2 solar masses never swell into red giants: as they use their hydrogen they grow slowly hotter and brighter for trillions of years, and end as helium white dwarfs :cite[lba97] :cite[al97]. None has done so yet; the universe is far too young. ## Planets and the habitable zone Because red dwarfs are faint, their habitable zones, where a rocky planet could keep liquid water, lie close in: about 0.27 to 0.52 AU for an M0 dwarf and about 0.06 to 0.11 AU for an M5 dwarf, using the conservative limits of Kopparapu et al. (2014) :cite[kopparapu2014]. A planet there orbits in days to weeks and is likely to be tidally locked, with one face towards its star. Small planets are common around red dwarfs, and they are easier to find than planets around Sun-like stars, because a small planet makes a larger dip or wobble in a small star. The three most famous red dwarfs all have rocky planets. **Proxima Centauri**, 4.25 light years away, has Proxima b, at least 1.07 Earth masses on an 11.2-day orbit in the habitable zone :cite[anglada16] :cite[faria22], and a candidate sub-Earth, Proxima d, on a 5.1-day orbit :cite[faria22]. **Barnard's Star**, the nearest single star to the Sun, has four confirmed sub-Earth-mass planets on orbits of 2.3 to 6.7 days :cite[gh24] :cite[basant25]; an earlier candidate on a 233-day orbit :cite[ribas18] was not borne out :cite[gh24]. **TRAPPIST-1**, a star of only 0.09 solar masses :cite[agol21], has seven Earth-sized planets :cite[gillon17]. JWST has found no thick carbon dioxide atmosphere on TRAPPIST-1 c :cite[zieba23], and its spectra of TRAPPIST-1 e, in the habitable zone, do not yet show whether that planet has an atmosphere at all :cite[glidden25]. See [[Habitable zone]] for how these limits are set. ::figure{src="File:TRAPPIST-1_system_PIA21751.jpg" size=wide alt="Artist's concept of seven rocky planets in a line in front of a small, dim red star" caption="Artist's concept: the seven planets of TRAPPIST-1, a red dwarf of 0.09 solar masses 40 light years away. Credit: NASA/JPL-Caltech."} ## How we know Red dwarfs are so faint that their true numbers came only from careful censuses of nearby space. Of the 337 stars within 10 parsecs, 249 are red dwarfs :cite[reyle21]. Their masses come from binary orbits and from relations calibrated on them; their radii from interferometry and eclipsing binaries. Proxima Centauri's orbit around the bright pair Alpha Centauri A and B takes about 550,000 years, confirming that the three stars are bound :cite[kervella17]. ## Notable examples | Star | Type | Distance | Mass (Sun = 1) | Notes | |---|---|---|---|---| | Proxima Centauri | M5.5Ve | 1.30 pc (4.25 ly) | 0.122 | Nearest star; flare star; planet b in the habitable zone :cite[kervella17] :cite[anglada16] | | Barnard's Star | M4V | 1.83 pc (5.96 ly) | | Four sub-Earth planets :cite[basant25] | | TRAPPIST-1 | M7.5 to M8V | 12.5 pc (40.7 ly) | 0.090 | Seven Earth-sized planets :cite[gillon17] :cite[agol21] | ::figure{src="File:Barnards_Star_planet_ESO_eso2414a.jpg" size=medium alt="Artist's impression of a small rocky planet in the foreground with a red dwarf star behind" caption="Artist's concept: one of the small planets orbiting Barnard's Star, the nearest single star to the Sun. Credit: ESO/M. Kornmesser."} :::callout{type=sim title="In Pax Abyssi"} Red dwarfs are the sim's red_dwarf class (code RDW), subdivided by temperature into early, mid and late M dwarfs and an ultracool class, each either quiet or active. The game's catalogue holds 6,530 real M-type stars, but because it lists stars bright enough to see, fewer than half of them are dwarfs; the procedural galaxy that fills in the rest of the Milky Way draws about three quarters of its stars from the red dwarf class, matching the local census. Proxima Centauri, Barnard's Star and the other nearby red dwarfs are catalogue stars at their Gaia distances. ::: ## See also - [[Stellar classification]] - [[K-type main-sequence star]] - [[Brown dwarf]] - [[Habitable zone]] - [[Planet occurrence]] - [[White dwarf]]