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Helium Fusion in Stars
An explanation of how elements on the periodic table, from
He to Fe, are produced in stars such as Red Giants and
Super Giants.
Red Giants
Main Sequence Stars,
such as Red Giants,
derive their energy
from hydrogen
fusion.
Eventually supply of
H runs out and core
consists entirely of
He
These stars
eventually collapse
into a white dwarf
Super Giant Stars
More massive stars
can evolve to become
Super Giants.
These are important
in the synthesis of
heavier elements up
to iron (Fe).
.
Helium Fusion:
The fusion of helium
atoms combine to
form carbon.
Helium fuses with
carbon to form oxygen.
This stops at iron,
because it has the
highest binding energy
and the addition of a
helium atom to an Fenucleus does not
generate energy
(rather, it consumes
it).
In the end, a core of an
exhausted Supergiant
will consist of iron
Chain of Helium Fusion
12
C + 4 He → 16 O
16
O + 4 He → 20 Ne
20
Ne + 4 He → 24 Mg
24
Mg + 4 He → 28 Si
24
Si + 4 He → 32 S Silicon Burning
32
S + 4 He → 36 Ar
36
Ar + 4 He → 40 Ca
40
Ca + 4 He → 44 Ti
44
Ti + 4 He → 48 Cr
48
Cr + 4 He → 52 Fe
Carbon Burning
Oxygen Burning
Formation of Odd Elements
Odd elements are not
formed through the
helium fusion
process in stars.
Even numbered
elements are more
stable (and therefore
more common) than
odd elements.
Odd numbered
elements can be
formed from
supernova
During a star’s
lifetime, it burns
heavier and heavier
elements.
Heavier elements
burn faster
(see table on right)
When it accumulates
Fe in the core and
can no longer
maintain a balance
of temperature and
pressure, the star
will undergo core
collapse and
explode into a
supernova
Conclusions
Summary
After hydrogen fusion, larger stars can continue with the fusion of
heavier elements.

Red Giants can fuse hydrogen and form helium.

Super Giant Stars can form elements from helium to iron.
The odd elements can be formed in supernova or through nuclear
decay.
Even elements are more common than odd elements.
After a star is exhausted of energy, its core will consist of Fe
(and outer shells of lighter elements).
Formation of Heavier Elements
An explanation of how elements heavier than Fe are
produced in supernovae
Periodic Table
The periodic table is
used to organize the
chemical elements by
their atomic number
Atomic number: sum
of protons.
Atomic Mass: sum of
the protons and
neutrons.
The origin of the
elements is in stars
and supernova
When the star’s core
consists of Fe, this
results in ‘core
collapse’ in which the
star beings to implode.
The energy released
results in a supernova
explosion.
This phenomenon
results in the
formation of elements
heavier than Fe.
Supernova Explosion
This image is titled
“The Pillars of
Creation” and was
taken by the Hubble
Telescope in 1995.
It is an image of a gas
and dust in the Eagle
Nebula.
It is an iconic image
and is a reminder
that the beginnings
of the Solar System
and life on Earth
come from these
primitive clouds of
dust and gas.
Made of Stars
Summary
 Elements heavier than iron (Fe) are formed during a supernova
explosion
The elements on the periodic table are organized according to their
atomic number (Z, which is equivalent to the number of protons).