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The Origin of the Elements and Earth
Published in Dexter Perkins, Kevin R. Henke, Adam C. Simon, Lance D. Yarbrough, Earth Materials, 2019
Dexter Perkins, Kevin R. Henke, Adam C. Simon, Lance D. Yarbrough
Stars of various sizes, including yellow stars like our Sun (an average star) and much larger blue giants (massive stars), condense from stellar nebulas of gas and dust (Fig. 1.10). Our Sun is about 4.6 billion years old and is about halfway through its life, but the life span of a star depends on its mass. The Sun and other yellow stars have life spans of about 9 billion years, but massive and hotter stars, called blue giants, rapidly consume their fuel and may die in less than 1 million years. Smaller stars are cooler, slowly consume their fuel, and have life spans of many billions of years. As the stars exhaust their fuel through nuclear fusion, they expand into red giants or supergiants. Eventually, reactions in the cores of the stars overcome gravity and the red giants and supergiants explode. Stars like our Sun will then become planetary nebulas composed of debris in a ring surrounding the remaining white dwarf star. Stars more massive than the Sun, eventually explode in what are called supernovas. The leftovers from supernovas may condense to form very dense, small radius (< 20 miles; 30 kilometers) neutron stars composed mostly of closely packed neutrons. The most massive supernovas, however, produce black holes. Black holes are so massive that not even light can escape their gravity.
Miscellaneous Algorithms
Published in Nazmul Siddique, Hojjat Adeli, Nature-Inspired Computing, 2017
In 1939, Robert Oppenheimer and Hartland Snyder published the first detailed treatment of a gravitational collapse, that is, when all thermonuclear sources of energy are exhausted, a sufficiently heavy star will collapse (Oppenheimer and Snyder, 1939). Using Einstein's theory of gravitation, it led to the idea that such an object might be formed by the collapse of a massive star that leaves behind a small and dense remnant core. If the core's mass is more than about three times the mass of the Sun, the equations showed that the force of gravity overwhelms all other forces and produces a black hole. The term black hole was itself coined in 1968 by Princeton physicist John Wheeler, who worked out further details of a black hole's properties. The most common black holes are probably formed by the collapse of massive stars. Larger black holes are thought to be formed by the sudden collapse or gradual accumulation of the mass of millions or billions of stars. Many galaxies are believed to have super massive black holes at their centers. There is a black hole at the center of our Milky Way galaxy, known as Sagittarius A*, has a mass 4 million times that of the solar mass. Most astronomers believe that the black holes in the centers of galaxies grew by swallowing stars and gas, emitting light in the process. But there is not enough light coming from the black holes in active galaxies to explain their growth (White and Diaz, 2004).
The Legacy of the Sun
Published in Wolfgang Palz, The Triumph of the Sun in 2000–2020, 2019
Our Sun is an average-size star. Those stars have a lifetime of some 10 billion years and end up as “red giants”. The larger a star is, the shorter is its lifetime. There are “massive stars” with 100 times the mass of our Sun; they live only a few million years before becoming a super giant star and exploding as a “supernova”. They can be 500,000 times as luminous as the Sun. Supernovae in turn end up as neutron stars or black holes. Black holes can have a billion times the mass of our Sun.
Improved black hole and multiverse algorithms for discrete sizing optimization of planar structures
Published in Engineering Optimization, 2019
Saeed Gholizadeh, Navid Razavi, Emad Shojaei
One of the newly developed metaheuristics is the BH algorithm (Hatamlou 2013). A black hole is a region of space with a huge amount of concentrated mass. Nothing falling into a black hole can escape from its gravitational pull and thus anything that enters a black hole is lost from the universe. The boundary of a black hole is known as the event horizon and if an object crosses its radius, the black hole absorbs it. The BH algorithm tries to simulate the above-mentioned phenomenon. The BH is a population-based algorithm and its basic steps are described below: