The Universe: Stars
A star is a massive, luminous ball of gas that is held together by its own gravity. The nearest star to Earth is the Sun. A star begins as a collapsing cloud of material composed primarily of hydrogen, along with helium and trace amounts of heavier elements. Once the stellar core is sufficiently dense, some of the hydrogen is steadily converted into helium through the process of nuclear fusion. For most of its life, a star shines due to thermonuclear fusion in its core releasing energy that traverses the star's interior and then radiates into space. Almost all elements heavier than hydrogen and helium were created by fusion processes in stars.
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Featured Article
Stellar Evolution - A History of Discovery
Introduction In 1906, Karl Schwarzschild published a fundamental paper in astronomy, describing the appearance of an incandescent, stable ball of gas in considerable detail, using basic principles...
Featured Resource
Interactive Tour: Stellar Evolution
The Milky Way galaxy contains several hundred billion stars of various ages, sizes and masses. A star forms when a dense cloud of gas collapses until nuclear reactions begin deep in the interior of the cloud and provide enough energy to halt the...
Latest News
No Place to Hide: Missing Primitive Stars Outside Milky Way Uncovered
GARCHING, GERMANY (Feb. 18, 2010) – After years of successful concealment, the most primitive stars outside our Milky Way galaxy have finally been unmasked. New observations using ESO’s...


