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===Helium Dwarf===

===Helium Dwarf===

''Helium dwarfs'' exist as a result of mass lose in a [[binary star|binary system]].<ref>http://adsabs.harvard.edu/abs/2005MNRAS.362..891B</ref> The helium white dwarf '''SDSS J091709.55+463821.8''', the least massive white dwarf known is an example of this.  It is part of a binary system where most of its mass has been lost to its more massive neighbor.   

''Helium dwarfs'' exist as a result of mass loss in a [[binary star|binary system]].<ref>http://adsabs.harvard.edu/abs/2005MNRAS.362..891B</ref> The helium white dwarf '''SDSS J091709.55+463821.8''', the least massive white dwarf known is an example of this.  It is part of a binary system where most of its mass has been lost to its more massive neighbor.   

Stars with less than 0.5 solar masses will never be able to fuse helium in their cores once all the hydrogen fuel is consumed.  It is theorized that they will also become helium white dwarfs, chiefly made up of helium-4 atoms.  Because such low-mass stars have such a long lifespan (on the order of around one trillion years for a low mass [[red dwarf]]), it is believed that none have completely consumed their core hydrogen fuel yet.<ref>http://spiff.rit.edu/classes/phys230/lectures/planneb/planneb.html</ref>

Stars with less than 0.5 solar masses will never be able to fuse helium in their cores once all the hydrogen fuel is consumed.  It is theorized that they will also become helium white dwarfs, chiefly made up of helium-4 atoms.  Because such low-mass stars have such a long lifespan (on the order of around one trillion years for a low mass [[red dwarf]]), it is believed that none have completely consumed their core hydrogen fuel yet.<ref>http://spiff.rit.edu/classes/phys230/lectures/planneb/planneb.html</ref>