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[[Image:RedDwarfNASA.jpg|thumb|right|200px|Artist rendition of a red dwarf star.]]

[[Image:RedDwarfNASA.jpg|thumb|right|200px|Artist rendition of a red dwarf star.]]

A '''red dwarf''' is a relatively cool and dim main sequence [[star]] of either spectral class M or late K.  Red dwarfs characteristically are the lowest mass stars in the main sequence, having less then one half of the mass of the [[Sun]], and may have as little as 0.075 times as much (any less and they would not be able to fuse hydrogen and instead becoming [[brown dwarf|brown dwarfs]]).<ref>http://spiff.rit.edu/classes/phys230/lectures/planneb/planneb.html</ref> Their surface temperatures averaging only around 2500 to 3500K. Red dwarfs are actually the most numerous class of stars in the [[galaxy]], making up more than half of all the stars including 21 of the 30 closest stars to our own [[Solar System]].<ref>http://www.daviddarling.info/encyclopedia/S/starsnearest.html</ref>

A '''red dwarf''' is a relatively cool and dim main sequence [[star]] of either spectral class M or late K.  Red dwarfs characteristically are the lowest mass stars in the main sequence, having less then one half of the mass of the [[Sun]], and may have as little as 0.075 times as much (any less and they would not be able to fuse hydrogen and instead becoming [[brown dwarf]]s).<ref>http://spiff.rit.edu/classes/phys230/lectures/planneb/planneb.html</ref> Their surface temperatures averaging only around 2500 to 3500K. Red dwarfs are actually the most numerous class of stars in the [[galaxy]], making up more than half of all the stars including 21 of the 30 closest stars to our own [[Solar System]].<ref>http://www.daviddarling.info/encyclopedia/S/starsnearest.html</ref>

Red dwarfs, unlike higher mass stars, generate most of their surface energy entirely through [[convection]], instead of [[radiation]].  This is due the density of the star in relation to temperature, making it difficult for energy to be transported to the surface through the radiation process from the core.  Because of this, red dwarfs can burn a proportionally higher percentage of their [[hydrogen]] fuel before evolving off of the main sequence.

Red dwarfs, unlike higher mass stars, generate most of their surface energy entirely through [[convection]], instead of [[radiation]].  This is due the density of the star in relation to temperature, making it difficult for energy to be transported to the surface through the radiation process from the core.  Because of this, red dwarfs can burn a proportionally higher percentage of their [[hydrogen]] fuel before evolving off of the main sequence.

===Planets around Red Dwarfs===

==Planets around Red Dwarfs==

[[File:Gliese 581.jpg|thumb|right|200px|Artist rendition of Gliese 581 and its planetary system.]]

[[File:Gliese 581.jpg|thumb|right|200px|Artist rendition of Gliese 581 and its planetary system.]]

As the most common type of star in the galaxy, astronomers long wondered if planets orbited any red dwarfs.  Since then several worlds have been found orbiting these stars including the small exoplanet orbiting the red dwarf star '''OGLE-2005-BLG-390L''' with a mass of only 5.5 times that of the Earth.<ref>http://www.nature.com/nature/journal/v439/n7075/full/nature04441.html</ref>  This was the smallest known exoplanet until the discovery of a planet in orbit of [[Gliese 581]] in 2009 called [[Gliese_581#Gliese_581_e|Gliese 581 e]], which has a mass only 1.9 times the Earth.<ref>http://exoplanets.org/planets.shtml</ref>  The red dwarf Gliese 581 also has a world, [[Gliese_581#Gliese_581_d|Gliese 581 d]], which is presently considered a decent candidate for habitability as it sits within the [[habitable zone]] of its parent star.<ref>http://cdsads.u-strasbg.fr/cgi-bin/nph-bib_query?2007A%26A...476.1365V&db_key=AST&nosetcookie=1</ref>

As the most common type of star in the galaxy, astronomers long wondered if planets orbited any red dwarfs.  Since then several worlds have been found orbiting these stars including the small exoplanet orbiting the red dwarf star '''OGLE-2005-BLG-390L''' with a mass of only 5.5 times that of the Earth.<ref>http://www.nature.com/nature/journal/v439/n7075/full/nature04441.html</ref>  This was the smallest known exoplanet until the discovery of a planet in orbit of [[Gliese 581]] in 2009 called [[Gliese 581#Gliese 581 e|Gliese 581 e]], which has a mass only 1.9 times the Earth.<ref>http://exoplanets.org/planets.shtml</ref>  The red dwarf Gliese 581 also has a world, [[Gliese 581#Gliese 581 d|Gliese 581 d]], which is presently considered a decent candidate for habitability as it sits within the [[habitable zone]] of its parent star.<ref>http://cdsads.u-strasbg.fr/cgi-bin/nph-bib_query?2007A%26A...476.1365V&db_key=AST&nosetcookie=1</ref>

It is debated whether red dwarfs could have planets favorable to life as we understand it.  This is due to the requirement that a [[habitable zone]] of red dwarf being extremely close to the star, due to the their low energy outputs.  For planets close enough to be within a red dwarf's habitable zone, it would most likely be [[tidal lock|tidally locked]] to its parent star, allowing for potential extremes in temperature between the day and night sides.  Red dwarfs also put out most of their energy in the form of [[infrared]] radiation, making [[photosynthesis]] very difficult, however this assumes a similar evolution of plant life.  The greatest potential danger to possible life on such a close world is the fact many red dwarfs are [[flare star|flare stars]].  Flare stars occasionally increase their brightness for a few minute, but the real danger is the corresponding sudden increase of radiation across the [[electromagnetic spectrum]], including [[ultraviolet]] and [[x-ray]] radiation.

It is debated whether red dwarfs could have planets favorable to life as we understand it.  This is due to the requirement that a [[habitable zone]] of red dwarf being extremely close to the star, due to the their low energy outputs.  For planets close enough to be within a red dwarf's habitable zone, it would most likely be [[tidal lock|tidally locked]] to its parent star, allowing for potential extremes in temperature between the day and night sides.  Red dwarfs also put out most of their energy in the form of [[infrared]] radiation, making [[photosynthesis]] very difficult, however this assumes a similar evolution of plant life.  The greatest potential danger to possible life on such a close world is the fact many red dwarfs are [[flare star]]s.  Flare stars occasionally increase their brightness for a few minute, but the real danger is the corresponding sudden increase of radiation across the [[electromagnetic spectrum]], including [[ultraviolet]] and [[x-ray]] radiation.

[[Category:Astronomy]]

[[Category:Astronomy]]