Thursday, March 20, 2008


Bright Stars
Red Giants
White Dwarfs
Birth of a Star
Protostars are stars that are about to be born. These are glowing clouds of interstellar gas and dust, which look like dark spots in the midst of light. Gravity causes every atom and every bit of dust to pull on every other one and all move to the center, causing the protostar to collapse. Having begun with a diameter of perhaps 1.5 trillion km, the protostar now shrinks at a very fast rate about 1,000 years, to a diameter of about 80 million km. Because the atoms move faster and faster as they fall toward the center, friction is created as they rub together and the temperature rises. The protostar starts at a temperature of about 100 K and over 1.000 years, rises to about 4,250 K. This heat causes the protostar to glow in with its own light, giving off even more light than our Sun even though it is not nearly as hot. After about 10,000 years, the protostar’s surface temperature is up to about 4,500 K and it is now 100 times as luminous as the Sun; after another 100,000 years the temperature is 5,000 K even though the protostar has been shrinking the entire time and only gives off about 10 times the light of the Sun. There is little change in temperature over the next 10 million years but the brightness continues to drop as the protostar contracts. The next 20 million years is the last stage of the protostar’s development where it equals the Sun in luminosity and its size becomes fixed at about 1.6 million km in diameter. 30 million years after the pocket of gas began to form, a star is born.
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