4. LEARNING COMPETENCIES
Learners will be able to…
•Give evidence for and describe the formation of
heavier elements during star formation and evolution
(S11/12PS-IIIb-11)
9. Nucleosynthesis
• Nucleosynthesis is the process of element (nuclei) formation.
• Three types: Big Bang nucleosynthesis
Stellar (star) nucleosynthesis
Supernova nucleosynthesis
• Today, only stellar and supernova nucleosynthesis are
occurring in our universe.
• Element formation in our universe relies on nuclear fusion
reactions.
(fusion = come together)
10. The Big Bang
• The Big Bang Theory is the most widely
accepted scientific theory about the origin of
the universe. It is supported by multiple lines
of evidence.
• The “Big Bang” was a phenomenally energetic
explosion that initiated the expansion of the
universe.
• At the moment prior to the Big Bang explosion,
all matter and energy were compressed at a
single point (a singularity – a point of infinite
density).
• We do not know what was before…..?
• The universe has been expanding ever since,
with galaxies moving farther and farther apart.
• Using the rates of expansion measured in the
universe and astronomical distances, the age
of the universe can be calculated back to the
time of the Big Bang. The age of the universe
is calculated at about 13.7 billion years old. By
contrast, our Sun and its surrounding planets
(i.e. our Solar System) is 4.65 billion years old.
11.
12. Big Bang Nucleosynthesis
• All Hydrogen and most Helium in the universe was produced
during the Big Bang Event, starting ~100 seconds after the
explosion. A small amount of Lithium was also produced.
• Big Bang nucleosynthesis ceased within a few minutes after
the Big Bang because the universe had expanded and cooled
sufficiently by then such that the temperatures and pressures
were too low to support additional nuclear fusion reactions.
13. Stellar Nucleosynthesis
• A star is a very hot ball of gas (plasma). Stars create elements by combining lighter nuclei into
heavier nuclei via nuclear fusion reactions in their cores and releasing energy in the process.
They are natural nuclear reactors!
• Enormous temperatures (15,000,000 K), pressures, and densities of matter are needed to
initiate the fusion (thermonuclear) reactions which squeeze nuclei together and release energy.
• The basic nuclear reaction in the Sun converts hydrogen to helium and releases energy in the
form of electromagnetic radiation (see the basic fusion reaction below). This is why our Sun
shines!
• Our Sun is only large enough to fuse hydrogen into helium within its core.
14. Activity 1
The word “stellar” means star and the formation of
elements in the center of the star is called stellar
nucleosynthesis. Carl Sagan said that “We are made of
star stuff.”
What did he mean by that? If we know how some
important heavy elements were formed same as stars,
that maybe a clue. Label the sequence of star life cycle.
Use the hints/clues found in the table below this
diagram.
15.
16. Hints/ Clues
Average Star
1. The star is unable to generate heat when it runs out of hydrogen in its core leading to its contraction and
expansion. It cools down and glows red. The Helium fused into Carbon. The star is now RED GIANT
2. Red giant star becomes exhausted of nuclear fuel, the outer material is blown off into space leaving the inert
Carbon. The remnant is known as WHITE DWARF.
3. Giant cloud of gas and dust known as NEBULA.
4. It is formed from nebula due to the gravity that pulled Hydrogen gas together until it spins faster and faster and
becomes ignited. A PROTOSTAR rises.
5. MAIN SEQUENCE STAR starts to form when nuclear fusion occurs at the core of the star, it begins to contract,
glow and become stable. Hydrogen is converted into Helium.
6. This is said to be the remain of the white dwarf that cooled down and no longer emits light and heat. The
hypothetical BLACK DWARF.
Massive star
1. It is believed that a NEUTRON STAR is formed from supernova explosion. This is also the smallest star
2. Explosion of star or SUPERNOVA releases large amount of energy. Because of that, elements are dispersed into
the space.
3. BLACK HOLE is a region in space where gravity is too strong that no matter can escape from it.
4. A more massive main sequence star evolves, cools and expands faster than low mass star and will turn into
RED SUPER GIANT star, the largest known star. Carbon fusion still occurs and Oxygen formed.
17. Hints/ Clues
Average Star
1. The star is unable to generate heat when it runs out of hydrogen in its
core leading to its contraction and expansion. It cools down and glows
red. The Helium fused into Carbon. The star is now RED GIANT
2. Red giant star becomes exhausted of nuclear fuel, the outer material is
blown off into space leaving the inert Carbon. The remnant is known as
WHITE DWARF.
3. Giant cloud of gas and dust known as NEBULA.
4. It is formed from nebula due to the gravity that pulled Hydrogen gas
together until it spins faster and faster and becomes ignited. A
PROTOSTAR rises.
5. MAIN SEQUENCE STAR starts to form when nuclear fusion occurs at
the core of the star, it begins to contract, glow and become stable.
Hydrogen is converted into Helium.
6. This is said to be the remain of the white dwarf that cooled down and
no longer emits light and heat. The hypothetical BLACK DWARF.
Massive star
1. It is believed that a NEUTRON STAR is formed from supernova
explosion. This is also the smallest star
2. Explosion of star or SUPERNOVA releases large amount of energy.
Because of that, elements are dispersed into the space.
3. BLACK HOLE is a region in space where gravity is too strong that no
matter can escape from it.
4. A more massive main sequence star evolves, cools and expands faster
than low mass star and will turn into RED SUPER GIANT star, the
largest known star. Carbon fusion still occurs and Oxygen formed.
18. Supernova Nucleosynthesis
• Elements heavier than Iron (Z = 26) are
made primarily when giant stars explode
in supernovae.
• Even the largest stars do not have core
temperatures and pressures high enough
to fuse iron into heavier elements.
Therefore, when a star runs out of
nuclear fuel (lighter nuclei) and can no
longer undergo fusion reactions, gravity
causes the star to collapse. The
gravitational collapse triggers a
phenomenally large explosion called a
supernova. The explosion of the star
momentarily generates high enough
temperatures and pressures to cause
nuclear fusion reactions that make
elements with atomic numbers 27-92
(Cobalt to Uranium).
• Since only the largest stars can explode in
supernovae events, elements with
atomic numbers 27-92 are rarer than
elements with atomic numbers 1-26
(see abundance diagram to right)
An exploded star
(supernova)
Relative Abundance of the Elements in our Universe
19. Nuclear Fusion
• In nuclear fusion, smaller nuclei collide together
to make larger nuclei, and energy is released in
the form of electromagnetic radiation.
• Requires extremely high temperatures and
pressures beyond those found on or within
Earth. However, these temperatures and
pressures are found inside stars and did occur
during the initial formation of our universe
(during the Big Bang event).
• Fusion involves only the nuclei of atoms. At the
temperatures at which fusion can occur, matter
exists as a plasma. This is the state of matter
where the electrons have been stripped off of
the atoms. Plasma is basically a super high
energy, electrically charged gas.
• When nuclei collide, some of the mass of the
nuclei is converted to energy by Einstein’s
famous equation, E=mc2. Nuclear fusion
releases a lot of energy per gram of material;
much more energy than is released by burning a
comparable amount of wood, coal, oil, or
gasoline!
20.
21. These will explain how stars are
formed into different stages because of
nuclear fusion (combination of nuclei to
form heavier one) among heavy
elements. The diagram shows the
Proton-Proton Chain reaction in main
sequence star. This is the process by
which average star gets their energy
and convert Hydrogen into Helium. It
starts with proton and neutron fused
together to form deuterium. When one
proton collides with deuterium,
Helium-3is formed. Two Helium-3
collided will form Helium-4.
22. CNO (Carbon, Nitrogen, Oxygen)
cycle to convert Hydrogen into Helium.
You can see at the right how Carbon 12
fused with proton (H) and form
Nitrogen-13. Nitrogen-13 undergoes
beta decay to form Carbon-13. Carbon-
13 captures proton (H) and Nitrogen 14
is formed. Nitrogen 14 captures proton
and Oxygen-15 is produced. Oxygen-15
undergoes beta decay and produces
Nitrogen-15. Nitrogen-15 fused with
proton gives off Helium and ends up
with Carbon-12. Then the process
repeats again.
23. CNO (Carbon, Nitrogen, Oxygen)
cycle to convert Hydrogen into Helium.
You can see at the right how Carbon 12
fused with proton (H) and form
Nitrogen-13. Nitrogen-13 undergoes
beta decay to form Carbon-13. Carbon-
13 captures proton (H) and Nitrogen 14
is formed. Nitrogen 14 captures proton
and Oxygen-15 is produced. Oxygen-15
undergoes beta decay and produces
Nitrogen-15. Nitrogen-15 fused with
proton gives off Helium and ends up
with Carbon-12. Then the process
repeats again.
24. CNO (Carbon, Nitrogen, Oxygen)
cycle to convert Hydrogen into Helium.
You can see at the right how Carbon 12
fused with proton (H) and form
Nitrogen-13. Nitrogen-13 undergoes
beta decay to form Carbon-13. Carbon-
13 captures proton (H) and Nitrogen 14
is formed. Nitrogen 14 captures proton
and Oxygen-15 is produced. Oxygen-15
undergoes beta decay and produces
Nitrogen-15. Nitrogen-15 fused with
proton gives off Helium and ends up
with Carbon-12. Then the process
repeats again.
25. Matter did not exist in the
beginning of the time; there
was only pure energy.
Question:
How did everything as we know it
today, come into being?
