supernova

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Explosive death of a star, which temporarily attains a brightness of 100 million Suns or more, so that it can shine as brilliantly as a small galaxy for a few days or weeks. Very approximately, it is thought that a supernova explodes in a large galaxy about once every 100 years. Many supernovae – astronomers estimate some 50% – remain undetected because of obscuring by interstellar dust.

The name ‘supernova’ was coined in 1934 by Swiss Astronomer Fritz Zwicky and German-born US astronomer Walter Baade. Zwicky was also responsible for the division into types I and II. Type I supernovae are thought to occur in binary star systems, in which gas from one star falls on to a white dwarf, causing it to explode. Type II supernovae occur in stars ten or more times as massive as the Sun, which suffer runaway internal nuclear reactions at the ends of their lives, leading to explosions. These are thought to leave behind neutron stars and black holes. Gas ejected by such an explosion causes an expanding radio source, such as the Crab nebula. Supernovae are thought to be the main source of elements heavier than hydrogen and helium.

The star depicts Liberia as a shining light. The blue canton symbolizes the dark continent of Africa. The stripes represent the 11 signatories to the Declaration of Independence. Effective date: 26 July 1847. >>