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Novas and supernovae they are stars that explode releasing part of their material in space. For a variable time, its brightness increases dramatically. It seems that a new star has been born.
A nova is a star that greatly increases its brightness suddenly and then pales slowly, but may continue to exist for some time. A supernova too, but the explosion destroys or alters the star. Supernovae are much rarer than novas, which are observed quite frequently in the photos.
Novas and supernovae provide materials to the Universe that will serve to form new stars.
Novas, new stars?
Formerly, a star that appeared suddenly where there was nothing, was called nova, or 'new star'. But this name is not correct, since these stars existed long before they could be seen with the naked eye.
10 or 12 novae may appear per year on the Milky Way, but some are too far away to be seen or obscured by interstellar matter.
Novas are seen more easily in other nearby galaxies than in ours. A nova increases its original brightness by several thousand times in a matter of days or hours. Then it enters a transition period, during which it pales, and becomes bright again; from there it pales little by little until it reaches its original level of brightness.
The novas are stars in a late period of evolution. They explode because their outer layers have formed an excess of helium through nuclear reactions and expands too quickly to be contained. The star explosively emits a small fraction of its mass like a layer of gas, increases its brightness and then normalizes.
The remaining star is a white dwarf, the smallest member of a binary system, subject to a continuous decline of matter in favor of the larger star. This phenomenon happens with dwarf novae, which arise again and again at regular intervals.
The explosion of a supernova is more destructive and spectacular than that of a nova, and much rarer. This is rare in our galaxy, and despite its incredible increase in brightness, few can be seen with the naked eye.
Until 1987, only three had been identified throughout history. The best known is the one that emerged in 1054 and whose remains are known as the Crab Nebula.
Supernovae, like novae, are seen more frequently in other galaxies. Thus, the most recent supernova, which appeared in the southern hemisphere on February 24, 1987, emerged in a satellite galaxy, the Large Magellanic Cloud. This supernova, which has unusual features, is the subject of intense astronomical study.
Very large stars explode in the last stages of their rapid evolution, as a result of a gravitational collapse. When the pressure created by nuclear processes, can no longer support the weight of the outer layers and the star explodes. It is called Type II supernova.
A Type I supernova originates similarly to a nova. It is a member of a binary system that receives the flow of fuel by capturing material from its partner.
There are few remains of the explosion of a supernova, except for the expanding layer of gases. A famous example is the Crab Nebula; In its center there is a pulsar, or neutron star that spins at high speed.
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