A supernova is a cataclysmic event that occurs as a result of the final uncontrolled nuclear reactions in a very high mass star at the end of its life. The giant star explodes violently due to the collapse of its core, hurtling all or most of its material outward at extremely high velocity. In some cases, a supernova will produce more light, for several weeks following the explosion, than the entire galaxy in which it resides. The remains of this titanic explosion consist of an expanding debris cloud and possibly an imploded remnant of the core, such as a neutron star, pulsar, or black hole.
M1, the Crab
Nebula, is the remnant of a supernova explosion that was observed by Chinese
astronomers in the year 1054. This supernova was so bright that it was
visible in broad daylight for several weeks. What remains of the core of
the star that produced the Crab Nebula is now a young optical pulsar with
a period of only 0.0331 seconds. The outer edges of the debris cloud are
expanding outward at over 600 miles per second.
The spiral
galaxy M81(NGC3031), in an exposure taken on 3/18/93.
The same
spiral galaxy, M81(3031), in an exposure taken twelve days later on 3/30/93,
showing a supernova that had exploded in one of the outer arms of the galaxy.
First seen by a group of astronomers in Spain, this supernova was independently
discovered by Ron Kohl, as reported in Circular #5736 from the Central
Bureau for Astronomical Telegrams at the Smithsonian Astrophysical Observatory
(International Astronomical Union). This supernova was officially designated
Supernova 1993J.
M51, the
Whirlpool Galaxy, in an image taken on 3/25/94.
The same
galaxy, M51, in an image taken on 4/8/94. In the two week interval between
these two images, a supernova explosion took place near the galactic nucleus.
Since this galaxy lies at a distance of approximately 20 million light
years, the explosion event took place about 20 million years ago.