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[[Image:White dwarf stars browse.jpg|thumb|White Dwarf Stars photographed by the Hubble Space Telescope.]]

[[Image:White dwarf stars browse.jpg|thumb|White Dwarf Stars photographed by the Hubble Space Telescope.]]

A '''White dwarf''' is a [[star]] that is the electron-degenerate remnant of a former star that has exhausted the nuclear fuel in its core and subsequently lost it's outer layers. They represent the final stage of [[Stellar_Evolution|stellar evolution]] for most stars, including our own [[Sun]].<ref>http://adsabs.harvard.edu/abs/2001PASP..113..409F</ref>    White dwarfs are extremely dense - a white dwarf with a mass equivalent to our Sun would have its material compacted into a volume no greater than the Earth.  As there is no more thermonuclear fusion within white dwarfs, their only source of [[light]] and [[heat]] is leftover thermal energy, as such, they will slowly cool and darken over billions of years.

A '''White dwarf''' is a [[star]] that is the electron-degenerate remnant of a former star that has exhausted the nuclear fuel in its core and subsequently lost it's outer layers. They represent the final stage of [[Stellar_Evolution|stellar evolution]] for most stars, including our own [[Sun]].<ref>http://adsabs.harvard.edu/abs/2001PASP..113..409F</ref>    White dwarfs are extremely dense - a white dwarf with a mass equivalent to our Sun would have its material compacted into a volume no greater than the Earth.  As there is no more thermonuclear fusion within white dwarfs, their only source of [[light]] and [[heat]] is leftover thermal energy.

Typically any star between 0.5 and 8 solar masses will end its life as a white dwarf.  Most of these dwarfs are primarily made up of [[carbon]] and [[oxygen]], however stars of 4 solar masses or more will have the ability to fuse carbon, which will result in a white dwarf chiefly made up of oxygen, [[neon]], and [[magnesium]].<ref>http://adsabs.harvard.edu/abs/2005ASPC..334..165W</ref>  Any star greater then 8 solar masses will eventually develop a core that will be too massive to support by electron-degeneratcy (the [[Chandrasekhar limit]]) and collapse.  This collapse will result in a [[supernova]], and depending on the star's mass, the end result will be a [[neutron star]] or a [[black hole]].

Typically any star between 0.5 and 8 solar masses will end its life as a white dwarf.  Most of these dwarfs are primarily made up of [[carbon]] and [[oxygen]], however stars of 4 solar masses or more will have the ability to fuse carbon, which will result in a white dwarf chiefly made up of oxygen, [[neon]], and [[magnesium]].<ref>http://adsabs.harvard.edu/abs/2005ASPC..334..165W</ref>  Any star greater then 8 solar masses will eventually develop a core that will be too massive to support by electron-degeneratcy (the [[Chandrasekhar limit]]) and collapse.  This collapse will result in a [[supernova]], and depending on the star's mass, the end result will be a [[neutron star]] or a [[black hole]].

==Fate of White Dwarfs==

==Fate of White Dwarfs==

As a white dwarf is no longer powered by thermonuclear fusion, all the light and heat generated is from remaining thermal energy.  Thus, the star will very slowly cool over time into a hypothetical ''black dwarf'', where it can no longer emit light or heat in significant quantities.  As the time period required for this to occur is longer than 13.7 billion years (the present lifespan of the [[universe]]), no black dwarf is expected to exist yet.  Even when the black dwarf state is reached, the stellar remnant itself is still expected to continue to exist indefinitely.

As a white dwarf is no longer powered by thermonuclear fusion, all the light and heat generated is from remaining thermal energy.  Thus, the star will very slowly cool over time into a hypothetical ''black dwarf'', where it can no longer emit light or heat in significant quantities.  As the time period required for this to occur is longer than 13.7 billion years, no black dwarf is expected to exist yet.  Even when the black dwarf state is reached, the stellar remnant itself is still expected to continue to exist indefinitely.

Sometimes white dwarfs, if they are in binary systems, may collide and fuse, forming a star that exceeds the Chandrasekhar limit and explode in a [[Supernova#Type_1a|type Ia supernova]].

Sometimes white dwarfs, if they are in binary systems, may collide and fuse, forming a star that exceeds the Chandrasekhar limit and explode in a [[Supernova#Type_1a|type Ia supernova]].

[[Adriaan Van Maanen]] discovered the first lone white dwarf in 1917, now named after him as [[Van Maanen's Star]].  Over time, several other faint white stars were discovered to have high proper motion, indicating they were relatively near the [[Solar System]], confirming them as white dwarfs as well.  The term white dwarf itself was first coined by [[Willem Luyten]] in his observation of these stars in 1922.<ref>http://adsabs.harvard.edu/abs/2005AAS...20720501H</ref>  By 1939 18 such stars were known, increasing to over 100 by 1950, and over 9,000 known today.

[[Adriaan Van Maanen]] discovered the first lone white dwarf in 1917, now named after him as [[Van Maanen's Star]].  Over time, several other faint white stars were discovered to have high proper motion, indicating they were relatively near the [[Solar System]], confirming them as white dwarfs as well.  The term white dwarf itself was first coined by [[Willem Luyten]] in his observation of these stars in 1922.<ref>http://adsabs.harvard.edu/abs/2005AAS...20720501H</ref>  By 1939 18 such stars were known, increasing to over 100 by 1950, and over 9,000 known today.

The [[Hubble Space Telescope]], with its 2.4 meter mirror and advanced optics, has been successfully viewing white dwarfs with its Wide Field and Planetary Camera. In August of 1995, this camera observed more than 75 white dwarfs in the [[globular cluster]] M4 in the constellation [[Scorpius]]. These white dwarfs were so faint that the brightest of them was no more luminous than a 100 watt light bulb seen at the [[Moon|moon's]] distance. M4 is located 7,000 light years away, but is the nearest globular cluster to Earth. It is also approximately 14 billion years old, which is why so many of its stars are near the end of their lives.

The [[Hubble Space Telescope]], with its 2.4 meter mirror and advanced optics, has been successfully viewing white dwarfs with its Wide Field and Planetary Camera. In August of 1995, this camera observed more than 75 white dwarfs in the [[globular cluster]] M4 in the constellation [[Scorpius]]. These white dwarfs were so faint that the brightest of them was no more luminous than a 100 watt light bulb seen at the [[Moon|moon's]] distance.  

== Sources ==

== Sources ==