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"That's easy," he said, and started to explain the various life cycles of the different types of stars. He told a fascinating story.
"If only Natalia would come early too!" I kept saying to myself. I knew she would love to hear his explanations. Since I had long been familiar with the ship's telescope, I was able to find examples of what he was talking about, with his guidance of course.
"It depends on the size of a planet," he said, "which in turn depends on the density of the clouds of gas and dust that are present in the expanding arms of galaxies where the stars are formed. Gravitational attraction pulls the gas clouds together until they condense and collapse under their own gravity. That's when a star is born. The collapse generates heat, which ignites hydrogen fusion, provided that its mass is great enough to achieve the requisite temperatures." He said that if a star's mass was small, like that of Jupiter that holds barely a tenth of the mass of the sun, the internal heat is insufficient to ignite the hydrogen fusion reaction. Such a star, he said, would cool slowly into a brown dwarf that remains unchanged for an indefinite time.
"Such a relatively cold star, of course, can't be seen with a telescope," he commented.
But he said there are plenty enough stars that had become suns, that have made it to the nuclear furnace stage. "Any star with the approximate mass of our sun has a rather typical history," he said to me. "After it first ignites, the star goes through a jet phase where immense amounts of materials are blown away by its ignition explosions. The materials will subsequently condense into planets that, like the Earth orbit the Sun."
It was not difficult to find a star in its jet phase. We could even see the blobs of matter the star had spit out within its jet streams. "Some blobs have been observed with a size of up to five light years across," the man said. "A lump like this might, only much smaller, have been the cradle of the Earth," he added.
"Fascinating!" I said.
He said that a typical sun exhausts its hydrogen in about ten billion years; after which two things happen. With the explosion becoming halted, the outward pressure in the star subsides. At this stage a new cycle of collapse begins. It starts deep as its center is drawn into itself, heating up the central core in the process, just as it did before, only this time to much greater temperatures, so much so that its outer layers expand into a red giant. However, when the internal heat becomes sufficient to ignite helium into nuclear fusion, the star will burn again for another season. Eventually the internal pressure caused by the fusion process becomes great enough to drive the core apart. This goes on until its helium fusion stops. The result is that the core cools and contracts again and re-ignites itself, and so the planet pulsates for many thousands of years. "In this process the helium becomes fused into carbon and the star eventually dies. All what will remain of it is a slowly cooling white dwarf made of pure carbon, like a diamond in the sky, which such a star, being carbon, essentially like a diamond, ends up to be. That star may indeed become dead...."
I was fascinated by the man telling me all this, and especially so when we were able to find examples of the various stages of a star's development. Apparently, he wasn't finished yet. He leaned back, crossed his legs, and made himself comfortable as though he had just begun.
I wished Natalia had come by as she usually does after her shift. I told my newfound friend that his talk was most fascinating and that Natalia would certainly have loved to hear it.
"Fascinating!" he repeated. "Just wait!" he said. "You haven't 'seen' anything yet. A star of ten solar masses will go through the same process, but will continue on burning as a nuclear furnace way past the carbon stage. The greater its mass is, the greater will be the gravity that acts on a star's core, and the greater will be the temperature resulting from its contraction. A nuclear fusion furnace of ten solar masses will reach a stage where its core becomes totally converted into iron." At this point he began to grin. "Here it becomes interesting." He said that iron has a special quality. He said it absorbs energy rather than releasing it, which causes a phenomenal thing to happen. "As the core contracts more and more, storing up energy in its iron atoms, a point will be reached when the gravity becomes so great that it literally crushes the atomic structure at the center of the star. Suddenly all the stored energy is released. The supercharged core rebounds, and in less than a second throws off its entire energy in the form of immense shock waves that will so superheat the outer envelope of the star that the entire star literally explodes. The end result is a super nova, a fireball of immense size and of a brilliance that is greater than a billion suns combined. In a stellar holocaust of such proportions all the rest of the heavy elements are concocted, including some that will eventually decay into uranium."
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