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Line 9: − − ===Our sun's fate as a red giant=== − − In an estimated 5 billion years our sun will have burned through its hydrogen fuel needed for nuclear fusion and enter into the red giant phase itself<ref>http://articles.adsabs.harvard.edu/cgi-bin/nph-iarticle_query?1993ApJ...418..457S&data_type=PDF_HIGH&whole_paper=YES&type=PRINTER&filetype=.pdf</ref>. The sun then will expand to an estimated 200 times its current diameter but will lose significant mass, perhaps sufficiently that the Earth's orbit will widen enough so as not to be swallowed by the expanding red giant, due to its weakened gravity, although this is debated.<ref>http://www.newscientist.com/article/dn13369?feedId=online-news_rss20</ref> If the Earth does survive, intact, the red giant phase of the sun, its atmosphere will be stripped and the surface will become hot enough to be molten. A few billion years before this stage, however, the Earth's biosphere will have already been destroyed by the sun as it grows ever more luminous over time.<ref>http://www.harmsy.freeuk.com/sun.html</ref> Eventually, the sun will consume all of its helium fuel and expel its outer layers, entering its final phase of life as a white dwarf.
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Low mass [[red dwarf|red dwarfs]] will not have sufficient mass to fuse helium and thus never enter a red giant phase, but instead will simply cool over time once all the hydrogen fuel is consumed.
Low mass [[red dwarf|red dwarfs]] will not have sufficient mass to fuse helium and thus never enter a red giant phase, but instead will simply cool over time once all the hydrogen fuel is consumed.
[[Category:Astronomy]]
[[Category:Astronomy]]