A white dwarf is a small star composed mostly of electron-degenerate
matter. Because a white dwarf's mass is comparable to that of the Sun
and its volume is comparable to that of the Earth, it is very dense.
Their faint luminosity comes from the emission of stored heat. They
comprise roughly 6% of all known stars in the solar neighborhood. The
unusual faintness of white dwarfs was first recognized in 1910 by Henry
Norris Russell, Edward Charles Pickering and Williamina Fleming. White
dwarfs are thought to be the final evolutionary state of all stars
whose mass is not too high. The material in a white dwarf no longer
undergoes fusion reactions, so the star has no source of energy, nor is
it supported against gravitational collapse by the heat generated by
fusion. It is supported only by electron degeneracy pressure, causing
it to be extremely dense. The physics of degeneracy yields a maximum
mass for a nonrotating white dwarf, the Chandrasekhar
limit—approximately 1.4 solar masses—beyond which it cannot be
supported by degeneracy pressure. Over a very long time, a white dwarf
will cool to temperatures at which it will no longer be visible, and
become a cold black dwarf.
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Today's selected anniversaries:
The Augsburg Confession, the primary confession of faith of the
Lutheran Church, was presented to the Holy Roman Emperor Charles V at
the Diet of Augsburg.
Black Hills War: United States Army Colonel George Armstrong Custer
was killed at the Battle of the Little Bighorn in present-day Big Horn
Douglas Hyde became the first President of Ireland after the office was
established by the Constitution of Ireland in 1937.
The Khobar Towers bombing in Khobar, Saudi Arabia, left 19 American
servicemen dead and 372 of many nationalities wounded.
Israeli soldier Gilad Shalit was kidnapped by Palestinian militants in
a cross border raid from the Gaza Strip on the crossing Kerem Shalom,
and has been held hostage by Hamas since.
Wiktionary's word of the day:
1. Tediously lengthy.
2. Tending to use large or obscure words, which few understand
Wikiquote quote of the day:
By "nationalism" I mean first of all the habit of assuming that human
beings can be classified like insects and that whole blocks of millions
or tens of millions of people can be confidently labelled "good" or
"bad." ... By "patriotism" I mean devotion to a particular place and a
particular way of life, which one believes to be the best in the world
but has no wish to force on other people. Patriotism is of its nature
defensive, both militarily and culturally. Nationalism, on the other
hand, is inseperable from the desire for power.
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