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Encyclopedia > Red dwarf
An artist's conception of a red dwarf star. Red dwarfs constitute the majority of all stars
An artist's conception of a red dwarf star. Red dwarfs constitute the majority of all stars

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. They constitute the vast majority of stars and have a mass of less than one-half that of the Sun (down to about 0.075 solar masses, which are brown dwarfs) and a surface temperature of less than 3,500 K. Red Dwarf is a British science fiction comedy franchise, the primary form of which comprises eight series of a post-watershed television sitcom that ran on BBC2 between 1988 and 1999, and which has achieved a global cult following. ... Image File history File links No higher resolution available. ... Image File history File links No higher resolution available. ... The Hertzsprung-Russell diagram (usually referred to by the abbreviation H-R diagram or HRD, also known as a Colour-Magnitude diagram, or CMD) shows the relationship between absolute magnitude, luminosity, classification, and effective temperature of stars. ... For other uses, see Temperature (disambiguation). ... This article is about the astronomical object. ... Hertzsprung-Russell diagram The main sequence of the Hertzsprung-Russell diagram is the curve where the majority of stars are located in this diagram. ... In astronomy, stellar classification is a classification of stars based initially on photospheric temperature and its associated spectral characteristics, and subsequenly refined in terms of other characteristics. ... Sol redirects here. ... This brown dwarf (smaller object) orbits the star Gliese 229, which is located in the constellation Lepus about 19 light years from Earth. ... For other uses, see Kelvin (disambiguation). ...

Contents

Description and characteristics

An artist's impression of a planet in orbit around a red dwarf
An artist's impression of a planet in orbit around a red dwarf

Red dwarfs are very low mass stars with no more than 40% of the mass of the Sun.[1] Consequently they have relatively low temperatures in their cores and energy is generated at a slow rate through nuclear fusion of hydrogen into helium via the proton-proton (PP) chain mechanism. Thus these stars emit little light, sometimes as little as 1/10,000th that of the Sun. But even the largest red dwarf has only about 10% of the Sun's luminosity.[2] Image File history File links RedDwarfPlanet. ... Image File history File links RedDwarfPlanet. ... In astronomy, the solar mass is a unit of mass used to express the mass of stars and larger objects such as galaxies. ... The deuterium-tritium (D-T) fusion reaction is considered the most promising for producing sustainable fusion power. ... This article is about the chemistry of hydrogen. ... General Name, symbol, number helium, He, 2 Chemical series noble gases Group, period, block 18, 1, s Appearance colorless Standard atomic weight 4. ... Overveiw of the proton-proton chain. ... The solar luminosity, , is a unit of luminosity (power emitted in the form of photons) conventionally used by astronomers to give the luminosities of stars. ...


In general red dwarfs transport energy from the core to the surface by convection. Convection occurs because of opacity of the interior, which has a relatively high density compared to the temperature. As a result, it is more difficult for photons to travel toward the surface by radiative processes. Convection takes over energy transport because it is a more efficient process.[3] Convection in the most general terms refers to the movement of currents within fluids (i. ... A substance or object that is opaque is neither transparent nor translucent. ... In modern physics the photon is the elementary particle responsible for electromagnetic phenomena. ...


As red dwarfs are fully convective, helium does not accumulate at the core and, compared to larger stars such as the Sun, they can burn a larger proportion of their hydrogen before leaving the main sequence. Thus red dwarfs have an enormous estimated lifespan; from tens of billions up to trillions of years depending upon mass. These lifespans are longer than the estimated age of the universe. The lower the mass of a red dwarf, the longer the lifespan.[1] As the proportion of hydrogen in a red dwarf is consumed, the rate of fusion declines and the core starts to contract. The gravitational energy generated by this size reduction is converted into heat, which is carried throughout the star by convection.[4] Hertzsprung-Russell diagram The main sequence of the Hertzsprung-Russell diagram is the curve where the majority of stars are located in this diagram. ...

Image File history File links This is a lossless scalable vector image. ...

Hertzsprung-Russell Diagram
Red dwarfs

The fact that red dwarfs and other low mass stars remain on the main sequence while more massive stars have moved off the main sequence allows the age of star clusters to be estimated by finding the mass at which the stars turn off the main sequence. This provides a lower, stellar, age limit to the Universe and also allows formation timescales to be placed upon the structures within the Milky Way galaxy, namely the Galactic halo and Galactic disk. The Hertzsprung-Russell diagram (usually referred to by the abbreviation H-R diagram or HRD, also known as a Colour-Magnitude diagram, or CMD) shows the relationship between absolute magnitude, luminosity, classification, and effective temperature of stars. ... In astronomy, stellar classification is a classification of stars based initially on photospheric temperature and its associated spectral characteristics, and subsequently refined in terms of other characteristics. ... This brown dwarf (smaller object) orbits the star Gliese 229, which is located in the constellation Lepus about 19 light years from Earth. ... This article or section does not adequately cite its references or sources. ... A subdwarf star, sometimes denoted by sd, is luminosity class VI under the Yerkes spectral classification system. ... Hertzsprung-Russell diagram The main sequence of the Hertzsprung-Russell diagram is the curve where the majority of stars are located in this diagram. ... Hertzsprung-Russell diagram The main sequence of the Hertzsprung-Russell diagram is the curve where the majority of stars are located in this diagram. ... Subgiant are Olly Maw, Dan Hayes and Tushar Joshi, a live dance music band from the UK formed in 2000. ... Giant star is a star that has stopped fusing hydrogen in its core. ... The luminosity class II in the Yerkes spectral classification is given to bright giants. ... Supergiants are the most massive stars. ... This article does not cite its references or sources. ... In astronomy, absolute magnitude is the apparent magnitude, m, an object would have if it were at a standard luminosity distance away from us, in the absence of interstellar extinction. ... In astronomy, absolute magnitude is the apparent magnitude, m, an object would have if it were at a standard luminosity distance away from us, in the absence of interstellar extinction. ... In astronomy, absolute magnitude is the apparent magnitude, m, an object would have if it were at a standard luminosity distance away from us, in the absence of interstellar extinction. ... In astronomy, absolute magnitude is the apparent magnitude, m, an object would have if it were at a standard luminosity distance away from us, in the absence of interstellar extinction. ... This article or section does not cite its references or sources. ... For other uses, see Universe (disambiguation). ... For other uses, see Milky Way (disambiguation). ... Spiral galaxies have a typical structure related to their history. ... The galactic plane is the plane in which the majority of a flattened galaxys mass lies. ...


One mystery which has not been solved as of 2007 is the absence of red dwarf stars with no metals. (In astronomy, a metal is any element heavier than hydrogen or helium). The Big Bang model predicts the first generation of stars should have only hydrogen, helium, and trace amounts of lithium. If such stars included red dwarfs, they should still be observable today, but none have yet been identified. The preferred explanation is that without heavy elements only large and not yet observed population III stars can form, and these rapidly burn out leaving heavy elements which then allow for the formation of red dwarfs. Alternative explanations, such as that zero-metal red dwarfs are dim and could be few in number, are considered much less likely as they seem to conflict with stellar evolution models. The globular cluster M80. ... For other uses, see Big Bang (disambiguation). ... Population III stars are a hypothetical population of extremely massive stars that are believed to have been formed in the early universe. ...


Red dwarfs are the most common star type in the Galaxy, at least in the neighborhood of the Sun. Proxima Centauri, the nearest star to the Sun, is a red dwarf (Type M5, apparent magnitude 11.05), as are twenty of the next thirty nearest. However, due to their low luminosity, individual red dwarfs cannot easily be observed over the vast interstellar distances that luminous stars can; in fact, none are visible to the naked eye.[5] Proxima Centauri (Latin proximus, -a, -um: meaning next to or nearest to)[4] is a red dwarf star that is likely a part of the Alpha Centauri star system and is the nearest star to the Sun at a distance of 4. ... This list of the nearest stars to Earth is ordered by increasing distance out to a maximum of 5 parsecs (16. ...


Planets

Extrasolar planets were discovered orbiting the red dwarf Gliese 581 in 2005, about the mass of Neptune, or seventeen earth masses. It orbits just 6 million kilometers (0.04 AU) from its star, and so is estimated to have a surface temperature of 150 °C, despite the dimness of the star. In 2006, an even smaller extrasolar planet (only 5.5 times the mass of Earth) was found orbiting the red dwarf OGLE-2005-BLG-390L; it lies 390 million km (2.6 AU) from the star and its surface temperature is −220 °C (56 K). Infrared Image of a possible extrasolar planet (lower left) in the Constellation Taurus, taken by the Hubble Space Telescope. ... Gliese 581 (IPA: ) is an M2. ... For other uses, see Neptune (disambiguation). ... A kilometre (American spelling: kilometer) (symbol: km) is a unit of length equal to 1000 metres (from the Greek words khilia = thousand and metro = count/measure). ... The astronomical unit (AU or au or a. ... For other uses, see Celsius (disambiguation). ... OGLE-2005-BLG-390Ls location in the night sky OGLE-2005-BLG-390L is a star thought to be a spectral type M - red dwarf star (95% probability, 4% probability it is a white dwarf, <1% probability it is a neutron star or black hole), and massing 0. ... For other uses, see Kelvin (disambiguation). ...


In 2007, a new, potentially habitable extrasolar planet, Gliese 581 c, was found, orbiting Gliese 581. If the mass estimated by its discoverers (a team led by Stephane Udry), namely 5.03 times that of the Earth, is correct, it is the smallest extrasolar planet revolving around a normal star discovered to date. (There are smaller planets known around a neutron star, named PSR B1257+12.) The discoverers estimate its radius to be 1.5 times that of the Earth. This planet is within the habitable zone of Gliese 581, and is the most likely candidate for habitability of any extrasolar planet discovered so far.[6] Understanding planetary habitability is partly an extrapolation of the Earths conditions, as it is the only planet currently known to support life. ... Gliese 581 c (IPA: ) is a super-earth extrasolar planet orbiting the red dwarf star Gliese 581. ... Gliese 581 (IPA: ) is an M2. ... Stéphane Udry (*1961 in Sion, Switzerland) is an astronomer at the University of Geneva in Switzerland, whose current work is primarily the search for extra-solar planets. ... For the story by Larry Niven, see Neutron Star (story). ... PSR B1257+12 (sometimes abbreviated to PSR 1257+12) is a pulsar located 980 light years from Earth. ... It has been suggested that Goldilocks phenomenon be merged into this article or section. ...


Habitability

Main article: Habitability of red dwarf systems‎

Planetary habitability of red dwarf star systems is subject to some debate.[citation needed] In spite of their great numbers and long lifespans, there are several factors which may make life difficult on planets around a red dwarf star. First, planets in the habitable zone of a red dwarf would be so close to the parent star that they would likely be tidally locked. This would mean that one side would be in perpetual daylight and the other in eternal night. This could create enormous temperature variations from one side of the planet to the other. Such conditions would appear to make it difficult for life (as we know it) to evolve.[citation needed] On the other hand, recent theories propose that either a thick atmosphere or planetary ocean could potentially circulate heat around such a planet. Determining the habitability of red dwarf systems could help reveal how likely extraterrestrial life is to exist, as red dwarfs make up a majority of all the stars in the galaxy. ... Understanding planetary habitability is partly an extrapolation of the Earths conditions, as it is the only planet currently known to support life. ... A separate article treats the phenomenon of tidal resonance in oceanography. ...


Another potential problem is that red dwarfs emit most of their radiation as infrared light, while on Earth plants use energy mostly in the visible spectrum. But, perhaps the most serious problem may be stellar variability. Red dwarfs are often covered in starspots, reducing stellar output by as much as 40% for months at a time. At other times, some red dwarfs, called flare stars, can emit gigantic flares, doubling their brightness in minutes. This variability may also make it difficult for life as we know it to survive near a red dwarf star. Gibor Basri of the University of California, Berkeley claims a planet orbiting close to a red dwarf star could keep its atmosphere even if the star flares. [1] For other uses, see Infrared (disambiguation). ... 400 year sunspot history A sunspot is a region on the Suns surface (photosphere) that is marked by a lower temperature than its surroundings, and intense magnetic activity. ... A flare star is a variable star which can undergo unpredictable dramatic increases in brightness for a few minutes or a few hours. ... Berkeley Davis Irvine Los Angeles Merced Riverside San Diego Santa Barbara Santa Cruz UC Office of the President in Oakland The University of California (UC) is a public university system in the state of California. ...


See also

Look up Red dwarf in
Wiktionary, the free dictionary.

Wiktionary (a portmanteau of wiki and dictionary) is a multilingual, Web-based project to create a free content dictionary, available in over 151 languages. ... Aurelia and Blue Moon are two fictional/hypothetical satellites on which extraterrestrial life could evolve. ... This brown dwarf (smaller object) orbits the star Gliese 229, which is located in the constellation Lepus about 19 light years from Earth. ... Artists conception of a cataclysmic variable system Cataclysmic variables (also U Geminorum Stars) are a class of binary stars containing a white dwarf and a companion star. ... The Hertzsprung-Russell diagram (usually referred to by the abbreviation H-R diagram or HRD, also known as a Colour-Magnitude diagram, or CMD) shows the relationship between absolute magnitude, luminosity, classification, and effective temperature of stars. ... A flare star is a variable star which can undergo unpredictable dramatic increases in brightness for a few minutes or a few hours. ... Nemesis is a hypothetical red dwarf star or brown dwarf, orbiting the Sun at a distance of about 50,000 to 100,000 AU, somewhat beyond the Oort cloud. ... According to the Hertzsprung-Russell diagram, a red giant is a large non-main sequence star of stellar classification K or M; so-named because of the reddish appearance of the cooler giant stars. ... Projected timeline of the Suns life In astronomy, stellar evolution is the process by which a star undergoes a sequence of radical changes during its lifetime. ... This article or section does not adequately cite its references or sources. ... In astronomy, stellar classification is a classification of stars based initially on photospheric temperature and its associated spectral characteristics, and subsequently refined in terms of other characteristics. ...

References

  1. ^ a b Richmond, Michael (November 10, 2004). Late stages of evolution for low-mass stars. Rochester Institute of Technology. Retrieved on 2007-09-19.
  2. ^ Chabrier, G.; Baraffe, I.; Plez, B. (1996). "Mass-Luminosity Relationship and Lithium Depletion for Very Low Mass Stars". Astrophysical Journal Letters 459: L91-L94. doi:10.1086/309951. 
  3. ^ Padmanabhan, Thanu (2001). Theoretical Astrophysics. Cambridge University Press, pp. 96-99. ISBN 0521562414. 
  4. ^ Koupelis, Theo (2007). In Quest of the Universe. Jones & Bartlett Publishers. ISBN 0763743879. 
  5. ^ http://kencroswell.com/thebrightestreddwarf.html "The Brightest Red Dwarf", by Ken Croswell (Accessed 6/7/08)
  6. ^ SPACE.com - Major Discovery: New Planet Could Harbor Water and Life

is the 314th day of the year (315th in leap years) in the Gregorian calendar. ... Year 2004 (MMIV) was a leap year starting on Thursday of the Gregorian calendar. ... Year 2007 (MMVII) was a common year starting on Monday of the Gregorian calendar in the 21st century. ... is the 262nd day of the year (263rd in leap years) in the Gregorian calendar. ... A digital object identifier (or DOI) is a standard for persistently identifying a piece of intellectual property on a digital network and associating it with related data, the metadata, in a structured extensible way. ... A digital object identifier (or DOI) is a standard for persistently identifying a piece of intellectual property on a digital network and associating it with related data, the metadata, in a structured extensible way. ... Year 2007 (MMVII) was a common year starting on Monday of the Gregorian calendar in the 21st century. ... is the 12th day of the year in the Gregorian calendar. ...

External links


  Results from FactBites:
 
Red dwarf - Wikipedia, the free encyclopedia (571 words)
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.
Red dwarfs never initiate helium fusion and so cannot become red giants; the stars slowly contract and heat up until all the hydrogen is consumed.
The fact that red dwarfs remain on the main sequence while older stars have moved off the main sequence allows one to date star clusters by finding the mass at which the stars turn off the main sequence.
Red Dwarf (2065 words)
RED DWARF has been voted by NME readers as their favourite TV series, and in the TGI Pilot Survey RED DWARF was 11-14 and 15-19 year olds' first choice.
Red Dwarf Night, a four hour special shown on BBC2, was broadcast to celebrate the show's 10th Anniversary on 14th February 1998.
RED DWARF has proven to be a massive international hit, not least in the USA where episodes have been broadcast in 48 states and it is currently available in 64% of US households.
  More results at FactBites »

 
 

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