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The Supernova of the Century
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13470 |
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Section : |
NATURAL SCIENCE
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| Issue
Date : |
9 / 1987 |
3,891 Words |
| Author
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Yoji Kondo
Yoji Kondo is NASA director of the International Ultraviolet
Explorer satellite observatory and professor of astronomy
and astrophysics at the University of Pennsylvania. |
Stars that seemingly appear out of nowhere and brighten to prominence in the night sky have fascinated astronomers since time immemorial. In Europe, where such a phenomenon was once thought to be the appearance of a new star, it was called a nova, a short form for stella nova. Once every few centuries there appeared extraordinarily bright ones, which came to be called supernovae. A supernova was sometimes visible even in the daytime. In China, novae and supernovae were called ke sin, or guest stars, stars that visited the heavens but briefly.
Although astronomers have puzzled over the nature of these mysterious objects for centuries, only during the past few decades have they come to understand the true nature of novae and supernovae. In February 1987 a supernova visible to naked eye observation appeared in the sky of the Southern Hemisphere. Because of its relative proximity and brightness, this supernova has provided a valuable opportunity to study a supernova in detail and identify its precursor for the first time in history.
The Discovery of Supernova 1987A
The brightest supernova observed since 1604 was detected on February 24, 1987, some 160,000 light-years away from earth in our sister galaxy, the Large Magellanic Cloud. The exploding star was discovered by Ian Shelton, an astronomer from the University of Toronto, who was observing at Las Companas Observatory in Chile. The region of the supernova had been photographed in the days before the explosion as part of the routine survey work of the observatory. Examination of photographs at the same exact location taken on February 22, two days before the first sighting revealed the presence of a 12th magnitude star much too dim for naked-eye viewing. By February 23, one day later, the star had already brightened to about the 6th magnitude, the faintest naked-eye visibility. Shelton had discovered the supernova at the moment of its explosion. The birth of a supernova, seen by Shelton, was not photographically recorded.
These observations and those by other astronomers nearly pinpoint the exact time of the initial brightening. The numerous photographs of the area prior to the supernova explosion will help us discover the progenitor of a supernova for the first time in history. In fact, it is quite likely that we already know which star exploded.
After the initial rapid brightening, the supernova increased its brightness slowly over a three-month period, from
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