L1 - Nucleosynthesis

• The Big Bang Model is the most prevailing model of the universe that states it began rapidly expanding 13.7 billion years ago. It also explains the formation of light elements
• The Orign of Chemical Elements - 1948, Ralph Alpher, Dr. Hans A. Bethe, and George Gamow

  states the process by which all elements in the universe formed after the big bang
• Big Bang Nucleosynthesis (aka Primordial Nucleosynthesis) refers to the production of nuclei
• H-1


  Hydrogen
• H-2

  Deuterium (hydrogen isotope)
• He-3, He-4


  Helium isotopes
• Li-7

  Lithium isotope
• Bigbang Nucleosynthesis lasted from 10 seconds to 20 minutes
• Hardon epoch


  1 nanosecond
• Between Hardon and Lepton epoch


  1 microsecond
• Lepton epoch


  1 millisecond
• Between Lepton epoch and Epoch of nucleosynthesis

  1 second
• Radiation domination

  1 hour
• The early universe's temperature was extremely high that fusion reaction was able to take place
• Fusion reaction


  two or more nuclei combine to form a new element
• In the Big Bang model, the first elements formed were hydrogen (H) and helium (He).
• The universe expanded and cooled to -10^10 Kelvin. The nuclear chemistry changed and no more neutrons formed. Their ratio relative to the stable protons then declined. Protons outnumbered the neutrons. At the low temperature, neutrons combined with protons to form hydrogen isotopes and deuterium
• deuterium nuclei is very reactive
• the expanding universe used to be an opaque plasma of photons, electrons, Hydrogen, Helium, and Lithium nuclei. As the temperature fell, electrons were able to combine with the atomic nuclei to form neutral atoms and made the universe optically clear
• A low mass star becomes a white dwarf in stellar nucleosynthesis
• a high mass star becomes either a neutron star (after a supernova) or a blackhole in stellar nucleosynthesis
• a star is formed when a cloud of gas and dust collapses and becomes dense, enabling nuclear fusion of hydrogen and helium nuclei to occur. The outflow of energy from this fusion provide pressure needed to halt and collapse. The pressure and gravity are in hydrostatic equillibrium
• The mass of the star controls its evolution and life span
• stars more massive than our sun may be main sequence stars for 10 million + years. stars less massive than our sun may be main sequence stars for 100 billion + years.
• the larger the star, the shorter the life span. the smaller the star, the longer the life span
• Red dwarf

  0.08 solar masses
• Sun


  1 solar mass
• Red giant

  <5 solar masses
• Blue-white super giant


  150 solar masses
• a star starts to die when hydrogen runs low
• Star Life Cycle: contraction of nebula due to gravity
• Protostar: temperature increases, after millions of years, gas becomes plasma and fusion begins
• Main sequence star: longest stage
• Nuclear fusion continues in the star's core
• Supergiant/giant: a star cools as it expands and glows red
• Low mass white dwarf: outer layers escape to space and the star collapses into a dense, hot, and dim star
• High mass white dwarf: nuclear fusion continues in the star's core until the star collapses into a black hole.
• Supernova: explosion of a supergiant
• Neutron star: small dense ball of neutrons that spin after the supernova
• Black hole: supernova remnants that are contracted; so dense light cannot escape from it