Origin of Elements

Origin of Elements Objectives: Explain the Big Bang Theory and provide evidence to support the theory. Explain the life cycle of a star. Explain how elements are produced from stars.

Origin of Elements Elemental composition of the visible universe 75% hydrogen 23% helium Atomic # Element ppm 1 Hydrogen 750,000 2 Helium 230,000 8 Oxygen 10,000 6 Carbon 5,000 10 Neon 1,300 26 Iron 1,100 7 Nitrogen 1,000 14 Silicon 700 12 Magnesium 600 16 Sulfur 500 1% oxygen 0.5% carbon

Origin of Elements The chemical makeup of the Sun changes over time, as hydrogen is converted to helium by nuclear fusion reactions in its core

The Big Bang Theory Our galaxy, the Milky Way, contains ~200 billion stars. Outside the Milky Way are billions more galaxies. There is evidence that the universe is expanding, so galaxies are moving farther away from each other. Thermal energy remains constant, so the universe is also cooling down. There is a large body of evidence supporting the Big Bang theory: 13.7 billion years ago all matter and energy was concentrated in one point. The “Big Bang” refers to the extraordinary explosion from that infinitesimal point.

The Big Bang Theory Beginning of the universe Initially Temperature too high; protons and neutrons could not form nuclei At 1 min Temperature had cooled enough; nuclei began to form At 3 min Temperature continued to drop; any free neutrons now bound to protons; already formed nuclei fused together After 3 min The elemental composition of the universe was “frozen” in place Calculations predict that hot nuclear plasma “freezing out” would give 75% hydrogen and 25% helium, with tiny amounts of lithium and beryllium – almost exactly what is observed in the visible universe.

Energy production on the Sun

Nucleosynthesis The Sun has been converting hydrogen to helium for the past 4.5 billion years, and continue to do so for the next 4.5 billion years. As the Sun runs out of hydrogen, the process will slow down, and the Sun’s core will get hotter and denser, and a new series of reactions will take place: Heavier nuclei will be created

Nucleosynthesis With heavier nuclei being formed by fusion, the core becomes hotter and more compressed. When it gets to the point of fusing iron (the most stable nucleus), the Sun will become unstable. Larger stars can explode as supernovas.