Supernova (Encyclopedia of Science)
Ancient astronomers assigned the word nova, Latin for "new," to any bright star that suddenly appeared in the sky. They called an extremely bright new star a supernova.
Modern astronomers now know that a supernova, one of the most violent events in the universe, is the massive explosion of a star. Only relatively large stars (those having 1.5 times the mass of our Sun or more) explode in supernovae at the end of their lives. Once a star has used up all its nuclear fuel, it begins to collapse in on itself. During this process, energy is released and the outer layers of the star are pushed out. These layers are large and cool, and the star at this point is considered a red giant. The star continues to expand, however, and soon explodes outward with great force. As a result of the explosion, the star sheds its outer atmospheric layers and shines more brightly than the rest of the stars in the galaxy put together.
What happens next depends on the original mass of the star. Stars up to three times the mass of the Sun end up as densely packed neutron stars or pulsars (rapidly rotating stars that emit varying radio waves at precise intervals). Stars more than three times the mass of the Sun collapse, in theory, to form a black hole (an infinite abyss from which nothing can escape).
(The entire section is 576 words.)
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