Creation of the universe!
Origin of the Chemical Elements
Stellar Nucleosynthesis and Supernovae Play Crucial Roles
You are recycled stardust. The atoms in our bodies were manufactured in stars or supernovae and recycled by supernova explosions.
The Big Bang Theory
The big bang formed only the four lightest elements. Protons, which are nuclei of hydrogen atoms, and electrons were made directly in the early stages of the big bang. Neutrons were made shortly thereafter when protons and electrons combined.
At the earliest stages the universe was still hot enough for hydrogen atoms to fuse into helium atoms, in reactions similar to those powering the Sun.
Atoms of heavier elements could not be manufactured until there was a significant amount of helium. However fusing helium into heavier elements requires higher temperatures and pressures than fusing hydrogen into helium. As the universe expands it cools, so by the time there was enough helium to fuse into heavier elements, it was too cool for the reactions to take place. Hence during the big bang only hydrogen, helium, and trace amounts of lithium and beryllium formed.
The other 88 elements were made later in stars and supernovae.
History
Hans Bethe and C.F. von Weizsacker independently deduced that stars fuse hydrogen into helium for their energy in the 1930s.
In the 1940s and early 1950s early proponents of the big bang theory, including George Gamow, Ralph Alpher, and Robert Herman, unsuccessfully tried to work out the detailed mechanisms to form heavier elements in the big bang. Eventually scientists realized that the universe cooled too fast to fuse heavier elements.
Hence heavy elements had to be made in stars. Margaret Burbidge, Geoffery Burbidge, William Fowler, and Fred Hoyle (often called BsquaredFH) published the detailed processes that stars use to manufacture the heavier elements in a huge 1957 paper.
Element Formation
Stars begin to die out when they can no longer fuse hydrogen to helium in their cores because the hydrogen fuel is exhausted. After the star expands into a red giant, the helium flash ignites helium fusion reactions in the core. Three helium atoms fuse into a carbon atom. Sometimes four heliums fuse into oxygen. Low mass stars, such as the Sun, cannot compress the core sufficiently to fuse heavier elements. Their carbon and oxygen is trapped when the star collapses into a white dwarf.
More massive stars play a more significant role because their greater mass can compress the core enough to fuse heavier elements. Carbon atoms can fuse into oxygen, neon, sodium, and magnesium. Some of the newly manufactured neon atoms fuse into oxygen and magnesium. Oxygen atoms can fuse into silicon and elements from magnesium to sulfur on the periodic table. These elements in turn produce elements near iron on the periodic table.
Fusion stops at iron, the boundary between fusion and fission. Fusing elements heavier than iron requires rather than releases energy.
There are two processes to manufacture elements heavier than iron. They are the slowly occurring s process and the rapidly occurring r process. One at a time, neutrons slam into atomic nuclei and subsequently decay into protons by releasing electrons. Adding a proton forms the next element on the periodic table.
Red giants last long enough for this s process to slowly manufacture elements as heavy as bismuth on the periodic table.
Elements heavier than bismuth can only be manufactured by the r process during a supernova. The successive fusion reactions leave an iron core, which collapses and rebounds. The rebound triggers a Type II supernova explosion that releases as much energy as the Sun does in 10 billion years and a very large number of neutrons. These neutrons rapidly slam into atomic nuclei and decay into protons. This r process manufactures elements heavier than bismuth.
The supernova blasts all these heavy atoms back into interstellar space. They are recycled into the nebulae forming the next generation of stars. Second and third generation stars, like the Sun, have planets containing elements, including those needed for life, not made during the big bang.
The death throes of massive stars sow the seeds for life in the universe. Like the legendary phoenix bird, new life in the universe springs from the ashes of ancient supernovae.
Further Reading
Zeilik, Michael, Astronomy the Evolving Universe, 9th edition, Cambridge, 2002.
Bartusiak, Marcia. Through a Universe Darkly, HarperCollins 1993.
Riordan, Michael and Schramm, David N. The Shadows of Creation, Freeman, 1991.
Origin of the elements
The fundamental reaction that produces the huge amounts of energy radiated by the Sun and most other stars is the fusion of the lightest element, hydrogen, its nucleus having a single proton, into helium, the second lightest and second most abundant, with a nucleus consisting of two protons and two neutrons. In many stars the production of helium is followed by the fusion of helium into heavier elements, up to iron. The still heavier elements cannot be made in energy-releasing fusion reactions; an input of energy is required to produce them.
The proportion of different elements within a star—i.e., its chemical composition—is gradually changed by nuclear fusion reactions. This change is initially concentrated in the central regions of the star where it cannot be directly observed, but it alters some observable properties of the star, such as brightness and surface temperature, and these alterations are taken as evidence of what is going on in the interior. Some stars become unstable and discharge some transmuted matter into interstellar space; this leads to a change in the chemical composition of the interstellar medium and of any stars subsequently formed. The main problem concerned with the origin of the chemical elements is to decide to what extent the chemical composition of the stars seen today differs from the initial chemical composition of the universe and to determine where the change in chemical composition has been produced. Reference is made in this article to the chemical composition of the universe, but most of the observations refer to our own and neighbouring galaxies.
Stellar Nucleosynthesis and Supernovae Play Crucial Roles
You are recycled stardust. The atoms in our bodies were manufactured in stars or supernovae and recycled by supernova explosions.
The Big Bang Theory
The big bang formed only the four lightest elements. Protons, which are nuclei of hydrogen atoms, and electrons were made directly in the early stages of the big bang. Neutrons were made shortly thereafter when protons and electrons combined.
At the earliest stages the universe was still hot enough for hydrogen atoms to fuse into helium atoms, in reactions similar to those powering the Sun.
Atoms of heavier elements could not be manufactured until there was a significant amount of helium. However fusing helium into heavier elements requires higher temperatures and pressures than fusing hydrogen into helium. As the universe expands it cools, so by the time there was enough helium to fuse into heavier elements, it was too cool for the reactions to take place. Hence during the big bang only hydrogen, helium, and trace amounts of lithium and beryllium formed.
The other 88 elements were made later in stars and supernovae.
History
Hans Bethe and C.F. von Weizsacker independently deduced that stars fuse hydrogen into helium for their energy in the 1930s.
In the 1940s and early 1950s early proponents of the big bang theory, including George Gamow, Ralph Alpher, and Robert Herman, unsuccessfully tried to work out the detailed mechanisms to form heavier elements in the big bang. Eventually scientists realized that the universe cooled too fast to fuse heavier elements.
Hence heavy elements had to be made in stars. Margaret Burbidge, Geoffery Burbidge, William Fowler, and Fred Hoyle (often called BsquaredFH) published the detailed processes that stars use to manufacture the heavier elements in a huge 1957 paper.
Element Formation
Stars begin to die out when they can no longer fuse hydrogen to helium in their cores because the hydrogen fuel is exhausted. After the star expands into a red giant, the helium flash ignites helium fusion reactions in the core. Three helium atoms fuse into a carbon atom. Sometimes four heliums fuse into oxygen. Low mass stars, such as the Sun, cannot compress the core sufficiently to fuse heavier elements. Their carbon and oxygen is trapped when the star collapses into a white dwarf.
More massive stars play a more significant role because their greater mass can compress the core enough to fuse heavier elements. Carbon atoms can fuse into oxygen, neon, sodium, and magnesium. Some of the newly manufactured neon atoms fuse into oxygen and magnesium. Oxygen atoms can fuse into silicon and elements from magnesium to sulfur on the periodic table. These elements in turn produce elements near iron on the periodic table.
Fusion stops at iron, the boundary between fusion and fission. Fusing elements heavier than iron requires rather than releases energy.
There are two processes to manufacture elements heavier than iron. They are the slowly occurring s process and the rapidly occurring r process. One at a time, neutrons slam into atomic nuclei and subsequently decay into protons by releasing electrons. Adding a proton forms the next element on the periodic table.
Red giants last long enough for this s process to slowly manufacture elements as heavy as bismuth on the periodic table.
Elements heavier than bismuth can only be manufactured by the r process during a supernova. The successive fusion reactions leave an iron core, which collapses and rebounds. The rebound triggers a Type II supernova explosion that releases as much energy as the Sun does in 10 billion years and a very large number of neutrons. These neutrons rapidly slam into atomic nuclei and decay into protons. This r process manufactures elements heavier than bismuth.
The supernova blasts all these heavy atoms back into interstellar space. They are recycled into the nebulae forming the next generation of stars. Second and third generation stars, like the Sun, have planets containing elements, including those needed for life, not made during the big bang.
The death throes of massive stars sow the seeds for life in the universe. Like the legendary phoenix bird, new life in the universe springs from the ashes of ancient supernovae.
Further Reading
Zeilik, Michael, Astronomy the Evolving Universe, 9th edition, Cambridge, 2002.
Bartusiak, Marcia. Through a Universe Darkly, HarperCollins 1993.
Riordan, Michael and Schramm, David N. The Shadows of Creation, Freeman, 1991.
Origin of the elements
The fundamental reaction that produces the huge amounts of energy radiated by the Sun and most other stars is the fusion of the lightest element, hydrogen, its nucleus having a single proton, into helium, the second lightest and second most abundant, with a nucleus consisting of two protons and two neutrons. In many stars the production of helium is followed by the fusion of helium into heavier elements, up to iron. The still heavier elements cannot be made in energy-releasing fusion reactions; an input of energy is required to produce them.
The proportion of different elements within a star—i.e., its chemical composition—is gradually changed by nuclear fusion reactions. This change is initially concentrated in the central regions of the star where it cannot be directly observed, but it alters some observable properties of the star, such as brightness and surface temperature, and these alterations are taken as evidence of what is going on in the interior. Some stars become unstable and discharge some transmuted matter into interstellar space; this leads to a change in the chemical composition of the interstellar medium and of any stars subsequently formed. The main problem concerned with the origin of the chemical elements is to decide to what extent the chemical composition of the stars seen today differs from the initial chemical composition of the universe and to determine where the change in chemical composition has been produced. Reference is made in this article to the chemical composition of the universe, but most of the observations refer to our own and neighbouring galaxies.
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