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Book: The Physics of Superheroes: Spectacular Second Edition by James Kakalios
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Authors: James Kakalios
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longer be a giant planet but rather a small star.
Big planets are gaseous because if you’re going to build a very big planet, you are going to need a lot of atoms, and when you go to the great celestial stockroom, nearly all of the raw materials available are either hydrogen or helium gas. To be precise, 73 percent of the elemental mass in the universe is hydrogen and 25 percent is helium. Everything else that you would use to make a solid planet—such as carbon, silicon, copper, nitrogen, and so on—comprises only 2 percent of the elemental mass in the known universe. So big planets are almost always gas giants, which tend to have orbits far from a star, where the weaker solar radiation cannot boil away the gaseous surfaces they have accreted. The concentration of heavier elements with which solid planets can form is much lower, so they will tend to be smaller and closer to a star. If these inner solid planets got too large, the gravitational tidal forces 13 from their sun would quickly tear them apart. Krypton’s advanced civilization, with scientists capable of constructing a rocket ship, couldn’t arise on a gas giant with a radius fifteen times that of Earth’s.
So, is that it? Is the story of Superman and Krypton, with an Earth-like surface and a gravity fifteen times that of Earth, totally bogus? Not necessarily. Remember that earlier it was stressed that no normal matter could be fifteen times denser than matter on Earth. However, astronomers have discovered exotic matter, with exceedingly high densities, formed from the remnants of supernova explosions. As mentioned, when the size of a gaseous planet exceeds a certain threshold, the gravitational compression at its center is so large that the nuclei of different atoms literally fuse together, creating larger nuclei and releasing excess energy in the process. The source of this energy is expressed in Einstein’s famous equation, E = mc 2 or Energy E is equivalent to mass m multiplied by the speed of light c squared. The mass of the fused-product nucleus is actually a tiny bit smaller than that of the two initial separate nuclei. The small difference in mass, when multiplied by the speed of light squared (a very big number) yields a large amount of energy. This energy radiates outward from the star’s center, producing an outward flow that balances the inward attractive gravitational force, keeping the radius of the star stable.
When all the hydrogen nuclei have been fused into helium nuclei, some of the helium nuclei are in turn fused into carbon nuclei, some of which in turn are compressed to form nitrogen, oxygen, and all of the heavier elements, up to iron. The fusion process speeds up as the star generates heavier and heavier nuclei, so that all of its iron and nickel are created within the last week of the star’s life. As heavier and heavier nuclei are combined, the process becomes less and less efficient, so that the energy released when iron nuclei fuse is insufficient to stably counteract the inward gravitational pressure. At this point gravity wins out, rapidly compressing the material into a much smaller volume. In this brief moment, the pressure at the center of the star is so high that one last gasp of fusion occurs, and heavier elements all the way up to uranium are generated, with a concurrent tremendous release of energy. This last stage in the life of the largest stars is termed the “supernova” phase. With this final blast of energy, the elements that had been synthesized within the star are flung out into space, where gravity may eventually pull them together into clumps that can form planets or other stars. Every single atom in your body, in the chair in which you are sitting, or the paper and ink in Action Comics # 1 , was synthesized within a star that died and subsequently expelled its contents. We are all composed of stardust or, if you’re feeling a tad more cynical, solar excrement.
For really big stars, the gravitational
Big planets are gaseous because if you’re going to build a very big planet, you are going to need a lot of atoms, and when you go to the great celestial stockroom, nearly all of the raw materials available are either hydrogen or helium gas. To be precise, 73 percent of the elemental mass in the universe is hydrogen and 25 percent is helium. Everything else that you would use to make a solid planet—such as carbon, silicon, copper, nitrogen, and so on—comprises only 2 percent of the elemental mass in the known universe. So big planets are almost always gas giants, which tend to have orbits far from a star, where the weaker solar radiation cannot boil away the gaseous surfaces they have accreted. The concentration of heavier elements with which solid planets can form is much lower, so they will tend to be smaller and closer to a star. If these inner solid planets got too large, the gravitational tidal forces 13 from their sun would quickly tear them apart. Krypton’s advanced civilization, with scientists capable of constructing a rocket ship, couldn’t arise on a gas giant with a radius fifteen times that of Earth’s.
So, is that it? Is the story of Superman and Krypton, with an Earth-like surface and a gravity fifteen times that of Earth, totally bogus? Not necessarily. Remember that earlier it was stressed that no normal matter could be fifteen times denser than matter on Earth. However, astronomers have discovered exotic matter, with exceedingly high densities, formed from the remnants of supernova explosions. As mentioned, when the size of a gaseous planet exceeds a certain threshold, the gravitational compression at its center is so large that the nuclei of different atoms literally fuse together, creating larger nuclei and releasing excess energy in the process. The source of this energy is expressed in Einstein’s famous equation, E = mc 2 or Energy E is equivalent to mass m multiplied by the speed of light c squared. The mass of the fused-product nucleus is actually a tiny bit smaller than that of the two initial separate nuclei. The small difference in mass, when multiplied by the speed of light squared (a very big number) yields a large amount of energy. This energy radiates outward from the star’s center, producing an outward flow that balances the inward attractive gravitational force, keeping the radius of the star stable.
When all the hydrogen nuclei have been fused into helium nuclei, some of the helium nuclei are in turn fused into carbon nuclei, some of which in turn are compressed to form nitrogen, oxygen, and all of the heavier elements, up to iron. The fusion process speeds up as the star generates heavier and heavier nuclei, so that all of its iron and nickel are created within the last week of the star’s life. As heavier and heavier nuclei are combined, the process becomes less and less efficient, so that the energy released when iron nuclei fuse is insufficient to stably counteract the inward gravitational pressure. At this point gravity wins out, rapidly compressing the material into a much smaller volume. In this brief moment, the pressure at the center of the star is so high that one last gasp of fusion occurs, and heavier elements all the way up to uranium are generated, with a concurrent tremendous release of energy. This last stage in the life of the largest stars is termed the “supernova” phase. With this final blast of energy, the elements that had been synthesized within the star are flung out into space, where gravity may eventually pull them together into clumps that can form planets or other stars. Every single atom in your body, in the chair in which you are sitting, or the paper and ink in Action Comics # 1 , was synthesized within a star that died and subsequently expelled its contents. We are all composed of stardust or, if you’re feeling a tad more cynical, solar excrement.
For really big stars, the gravitational
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