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Astronomers believe that molecular clouds, dense clouds of gas located primarily in the spiral arms of galaxies are the birthplace of stars. Dense regions in the clouds collapse and form "protostars". Initially, the gravitational energy of the collapsing star is the source of its energy. Once the star contracts enough that its central core can burn hydrogen to helium, it becomes a "main sequence" star. Main sequence stars are stars, like our Sun, that fuse hydrogen atoms together to make helium atoms in their cores. For a given chemical composition and stellar age, a stars' luminosity, the total energy radiated by the star per unit time, depends only on its mass. Stars that are ten times more massive than the Sun are over a thousand times more luminous than the Sun.
M assive stars distinguish themselves from their lower mass cousins by their eventual fate. Their subsequent evolution may lead to an explosion in the form of a core-collapse supernova, a long duration gamma-ray burst GRB or direct collapse to a black hole. But our physical understanding of transients remains rather patchy, and is reliant upon the far less glamorous field of stellar astrophysics. In this review, I shall set out some of the current issues relating to massive stars, involving their formation, evolution and ultimate demise. Extensive review articles on these topics include Zinnecker and Yorke , Maeder and Meynet , Smartt and Woosley and Bloom The lifetimes of massive stars are short up to a few tens of million years, see figure 1 because of their high luminosities, so their death rate closely mimics the stellar birth rate. Other nearby star-forming galaxies have hosted several SNe in the past century.
Stellar evolution is the process by which a star changes over the course of time. Depending on the mass of the star, its lifetime can range from a few million years for the most massive to trillions of years for the least massive, which is considerably longer than the age of the universe. The table shows the lifetimes of stars as a function of their masses. Over the course of millions of years, these protostars settle down into a state of equilibrium, becoming what is known as a main-sequence star. Nuclear fusion powers a star for most of its existence.
Life Cycle of a Star
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Life and Death of the Stars
It seems that you're in Germany. We have a dedicated site for Germany. This volume is devoted to one of the fascinating things about stars: how they evolve as they age. This evolution is different for stars of different masses.
The Life and Death of Stars
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Radio astronomy has helped astronomers explore the life stories of stars, and here is what we have learned so far. The color of a star is an indicator of its temperature. The cooler stars are brown to dark red, barely warmed enough to glow, like the cooling embers in a fire.
If the Solar System is rich in chemical elements other than H and He; where did they come from? J. Piekarewicz (FSU-Physics). The Birth, Life, and Death of Stars.
Main Sequence Stars
Stars are formed in clouds of gas and dust, known as nebulae. Nuclear reactions at the centre or core of stars provides enough energy to make them shine brightly for many years. The exact lifetime of a star depends very much on its size. Very large, massive stars burn their fuel much faster than smaller stars and may only last a few hundred thousand years. Smaller stars, however, will last for several billion years, because they burn their fuel much more slowly. Eventually, however, the hydrogen fuel that powers the nuclear reactions within stars will begin to run out, and they will enter the final phases of their lifetime.
Конечно. Алгоритм, не подающийся грубой силе, никогда не устареет, какими бы мощными ни стали компьютеры, взламывающие шифры. Когда-нибудь он станет мировым стандартом. Сьюзан глубоко вздохнула. - Да поможет нам Бог, - прошептала. - Мы можем принять участие в аукционе. Стратмор покачал головой: - Танкадо дал нам шанс.
Стратмор его не слушал. Если спасение Сьюзан равнозначно крушению его планов, то так тому и быть: потерять ее значило потерять все, а такую цену он отказывался платить. Хейл заломил руку Сьюзан за спину, и голова ее наклонилась.