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Origin of Elements
Origin of Elements
Objectives:
1. Explain the Big Bang Theory and provide evidence
to support the theory.
2. Explain the life cycle of a star.
3. Explain how elements are produced from stars.
Origin of Elements
Elemental composition
of the visible universe
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
75% hydrogen
23% helium
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.