Stars are the cosmic incubators for all natural elements
|
This book requires basic knowledge of physics and chemistry. Chapters 1 - 7 introduce cosmology; Chapters 8 - 9 describes evolution of stars, and physical and chemical process for the production of chemical elements; Chapters 10 - 13 addresses the evolution of life on hospitable planets such as earth. Chapters 8, 9 and 11 provide significant amount of information, while some chapters are too descriptive and boring.
When the universe was at its infancy, it consisted of clouds of hydrogen and helium molecules that started to collapse over millions of years (mass accretion) under gravity. Progressively the temperature increased due to compression and the molecules started to dissociate into atoms and finally to ions at high pressure and temperatures. At 15 million degrees, about one in a 100 million protons gain sufficient energy to collide and fuse with each other to produce deuterium nuclei, further nuclear reactions generated helium-3 nucleus. Collision of two helium-3 nuclei results in helium-4 and two protons, generating intense radiation (energy) and pressure (centrifugal force) to counter the gravitational (centripetal) force. Thus thermonuclear reactions produce heat and light of a star over billions of years of its existence which affects geological process and biological evolution in orbiting planets. If a star is massive, gravitational collapse continues and the temperature at inner core rises to 100 million degrees when two helium-4 nuclei fuse to form berylluim-8 nuclei; at higher core temperatures collision of helium-4 with beryllium-8 results in carbon-12. After millions of years of burning helium, the inner core continues to fall as the compression continues to raise core temperature and this promotes carbon-12 and helium-4 nuclear fusion producing oxygen-16 nucleus. When helium nuclei are completely exhausted; the star would have produced significant quantities of carbon and oxygen nuclei. This result in two shells; an inner core of carbon and oxygen followed by an outer shell of burning helium, which is surrounded by a shell of burning hydrogen. When helium is exhausted, the inner core is compressed further raising temperature, then two carbon nuclei fuse to produce a plethora of nuclei from oxygen to sodium and magnesium. When carbon burning is completely exhausted, the core compresses further raising temperature and pressure to promote fusion of oxygen nuclei to produce silicon, neon, and then sulfur. As the temperatures rises to one billion degrees, fusion of silicon nuclei results in iron-56 nucleus; beyond this point no further elements are generated, since heavier nuclei bind less tightly. At this stage when the temperature is 5 billion degrees, the density reaches 10,000 tons per cubic centimeter. The core starts to lose energy in the form escaping neutrinos, and fusion of protons and electrons results in increasing amounts of neutrons. As the core energy decreases, the gravitational force of matter dominates. At a density of 100 million tons per cubic centimeter, the core predominantly contains neutrons and at this point laws of quantum mechanics precludes neutrons squeezed any further thus forming a neutron star. Eventually the star collapses in a gigantic explosion called supernova. At this point the temperature is very high and during this hot expanding neutron-rich environment capture of neutrons by various elements quickly produces all natural elements up to uranium. These are expelled into the interstellar medium to great distances in spacetime, eventually cooling the debris. During cooling process; the nuclei capture electrons to become atoms and elements such as iron, silicon, aluminum and carbon will condense into microscopic solid grains at appropriate temperatures. Low molecular weight compounds such as carbon monoxide, iron oxides, silicates and water are formed at right temperatures and pressure. Photochemical reactions in presence of iron and aluminum produce carbon dioxide, methanol, ethanol, formaldehyde, and glycine (amino acid) etc. Carbon, hydrogen, oxygen and nitrogen continue to form more complex organic and biomolecules, the source material for life. Oxygen remains adhered to grains of aluminum oxide. As the stellar dust and gas collapse inward toward a central plane of rotating material which will fragment to form planetismals (planetary nebula) around a star. Much of water was provided by comets (from Oort clouds outside the solar system) hitting earth over millions of years. The planet turned from state of high levels of carbon dioxide and nitrogen to a more tolerable levels, and habitable temperatures which lead to the raise in oxygen concentration. It is a concerted effort of sun and the Jupiter; geological process followed by biological evolution created the blue planet. This book contains an exhaustive amount of scientific material that could serve as a reference material, and it is highly recommended.
|
|
|
United States | 
United Kingdom | 
Canada