2. Learn about It!
Cosmology is the body of science that studies the origin,
evolution and eventual fate of the universe
Cosmology
3. Learn about It!
Religious Cosmology
• Religious or mythological cosmology explains the
origin of universe and life based on religious beliefs of a
specific tradition
• The concept of creatio ex nihilo
• God creating the universe as written in the book of
Genesis
Cosmology
4. Learn about It!
Physical Cosmology
Physical cosmology explains the origin of universe based on
scientific insights, studies and experiments
• Nicolaus Copernicus and the heliocentric nature of the
universe
• The expanding universe through Albert Einstein’s theory
of relativity
• The big bang theory
Cosmology
5. Learn about It!
The big bang theory, a cosmological model that describes
how the universe started its expansion about 13.8 billion years
ago, states that the universe continues to move and expand
Big Bang Theory
6. Learn about It!
1. The universe began as a singularity or a point containing
all space, time, matter and energy
2. It expanded rapidly in nothingness through a rapid yet
peaceful process called inflation
3. The universe cooled down as it expanded
Big Bang Theory
7. Learn about It!
4. A soup of matter in the form of subatomic particles was
formed and nuclei of light atoms were created via
nucleosynthesis or nuclear fusion between protons
and neutrons
5. Electrons interacted with these nuclei to form actual,
primordial atoms via the process of recombination
Big Bang Theory
8. Learn about It!
Evidences
1. Vesto Slipher and Carl Wilhelm Wirtz (1910)
• Measurement of redshift
• Observed that most spiral galaxies were moving away
from the earth
2. Georges Lemaître (1927)
• Proposed alternative idea that the universe is
expanding
Big Bang Theory
9. Learn about It!
Evidences
3. Edwin Hubble (1929)
• Calculated distances between the earth and several
galaxies using redshift of light
• Observed distant galaxies were moving away from the
Earth and one another
Big Bang Theory
10. Learn about It!
Evidences
4. Robert Wilson and Arno Penzias (1965)
• Discovered cosmic microwave background
radiation (CMBR)—a low, steady humming noise
believed to be energy remains
5. Modern astronomy (2014)
• Universe is estimated to be 13.8 billion years old with
5% of its composition existing as ordinary matter
Big Bang Theory
11. Learn about It!
Big Bang Nucleosynthesis
• Big bang nucleosynthesis (BBN), also known as
primordial nucleosynthesis, is the process of producing
light elements during the big bang expansion
• It yields two stable isotopes of hydrogen, two isotopes of
helium, some lithium atoms and beryllium isotopes
Big Bang Theory
12. Learn about It!
Big Bang Nucleosynthesis
1. A proton (p) and a neutron (n) may fuse together to
yield a high-energy photon (γ) and an isotope of
hydrogen (H) called deuterium (D or 2H, with one p and
one n)
• The deuterium bottleneck can be traced to its low binding energy
and eventual destruction by photons at very high temperatures
• A decrease in temperature enabled deuterium to stabilize and
eventually initiate the BBN cascade
Big Bang Theory
13. Learn about It!
Big Bang Nucleosynthesis
2. Two D nuclei may fuse together to form either of the
following:
a. The radioactive H isotope tritium (T or 3H, with one p and two n) and
one p; or
b. The isotope helium-3 (He-3 or 3He, with two p and one n) along with
one n
Big Bang Theory
14. Learn about It!
Big Bang Nucleosynthesis
3. Helium-4 (He-4 or 4He, with two p and two n) may be
formed from three fusion reactions
a. The fusion of one p and a T atom
b. The fusion of D with T
c. The fusion of D with He-3
Big Bang Theory
15. Learn about It!
Big Bang Nucleosynthesis
• He-4 has a binding energy of 28 MeV, and further fusion
products were a rarity since these resulting atoms had
binding energies lower than this aforementioned amount
Big Bang Theory
16. Learn about It!
Big Bang Nucleosynthesis
4. He-4 may still undergo further fusion in the presence of a
T atom, yielding the lithium-7 atom (Li-7 or 7Li, with three
p and four n) and a γ
• Li-7 may react with one p to produce two stable He-4 nuclei
Big Bang Theory
17. Learn about It!
Big Bang Nucleosynthesis
5. He-4 may also fuse with He-3 to yield the unstable isotope
beryllium-7 (Be-7 or 7Be, with four p and three n) along
with one γ
Big Bang Theory
18. Key Points
The big bang theory is a cosmological model that
describes how the universe started its expansion
about 13.8 billion years ago.
1
Big bang nucleosynthesis is the process of producing
light elements during the big bang expansion.
2
The correlation between the predicted and observed
cosmic abundances of hydrogen and helium was the
major proof of the big bang theory.
3
20. Learn about It!
The BBN did not give rise to elements heavier than beryllium
• Drop in temperature resulted in insufficient energy levels
for fusion reactions to push through
• Nucleosynthesis continued with the expansion of the
universe
Big Bang Nucleosynthesis
21. Learn about It!
The star formation theory states that stars formed when
gravity acted on the particles expanding with the universe.
• Stellar nurseries form from dense molecular regions
• Protostars are formed when these regions collapse.
Stellar Formation
22. Learn about It!
• Elements associated with both living and nonliving things
mostly originated from stars
• Processes that occurred inside stars were responsible for
the formation of these elements
Stellar Nucleosynthesis
23. Learn about It!
• Elements heavier than beryllium were formed through
stellar nucleosynthesis
• H and He produced from BBN started to combine in
nuclear fusion reactions
• Very high amounts of energy were released in the form
of light, heat and radiation.
Stellar Nucleosynthesis
24. Learn about It!
Stellar evolution refers to the process in which a star changes
through its lifetime
• The abundances of elements a star contains change as it
evolves
• The course of evolution is determined by its mass
Stellar Evolution
25. Learn about It!
All stars are formed from stellar nurseries called nebulae
• A nebula breaks into smaller fragments as it further
collapses before contracting into a protostar, or a very hot
stellar core that continues to gather gas and dust as it
contracts and increases in temperature
• Nuclear reactions like the proton-proton fusion reactions
occur at a temperature of around 10 million K
Stellar Evolution
26. Learn about It!
Protostars evolve into main sequence stars upon reaching
gravitational equilibrium
• Nuclear reactions form subatomic particles called
neutrinos and positrons
• An increase in pressure brought about by positrons and
neutrinos halt the contraction of the protostar
Stellar Evolution
27. Learn about It!
The sun is believed to be in the middle of the main sequence
phase of stellar evolution
• It will remain as such for at least five billion years
• Red dwarf stars stay on the main sequence phase for at
least 100 billion years due to the slow rate of hydrogen
fusion
Stellar Evolution
28. Learn about It!
Not all protostars become main sequence stars
• Brown dwarf stars are only able to fuel deuterium fusion
reactions
• They cool gradually and have an average lifespan of less
than a billion years
Stellar Evolution
29. Learn about It!
Main sequence stars evolve into red giant stars when all
hydrogen atoms in their cores get depleted
1. Helium becomes the major component of the core.
• Proton-proton chain reactions use hydrogen to produce
helium
• Hydrogen fusion moves to the outer shell and the core's
surface
Stellar Evolution
30. Learn about It!
Main sequence stars evolve into red giant stars when all
hydrogen atoms in their cores get depleted
2. Fusion stops when all hydrogen atoms in the core are used
up
• Pressure in the core decreases
3. Helium atoms or alpha particles are converted to carbon
via the alpha fusion processes
Stellar Evolution
31. Learn about It!
Main sequence stars evolve into red giant stars when all
hydrogen atoms in their cores get depleted
4. Temperature can increase to approximately 10 million K
• Pressure also increases
• Hydrogen is pushed away from the core
• The resulting expansion eventually transforms the main
sequence star to a red giant
Stellar Evolution
32. Learn about It!
Main sequence stars evolve into red giant stars when all
hydrogen atoms in their cores get depleted
Fusion of elements in a red giant
Stellar Evolution
33. Learn about It!
Low mass stars turn into white dwarf stars when the majority
of helium in their cores are consumed
1. Hot and inert carbon core eventually becomes the white
dwarf
• Lower amounts of helium in the core decrease the rate of
the alpha processes
• Outer shell expands into space, forming a planetary
nebula
Stellar Evolution
34. Learn about It!
Low mass stars turn into white dwarf stars when the majority
of helium in their cores are consumed
2. A white dwarf’s composition depends on its predecessor’s
mass.
• A sun-sized main sequence star lacks energy to fuse
carbon and the white dwarf would mostly contain inert
carbon and some oxygen
• A smaller star will produce a white dwarf mostly
composed of helium and a bit of hydrogen
Stellar Evolution
35. Learn about It!
Massive stars evolve into multiple-shell red giant stars
1. A high mass star can reach pressure and temperature
levels favorable for carbon fusion
2. It evolves through several stages where heavier elements
are fused in the core and in the shells around it eventually
forming multiple shells
• Multiple elements formed in a series of reactions in the
following order: carbon → oxygen → neon → silicon →
iron
Stellar Evolution
36. Learn about It!
Massive stars evolve into multiple-shell red giant stars
3. Elements lighter than iron can be fused since the nucleus
produced has a mass lower than the sum of their masses
• Missing mass is released as energy
4. Stellar nucleosynthesis of elements heavier than iron is not
possible due to its energy requirement
Stellar Evolution
37. Learn about It!
Massive stars evolve into multiple-shell red giant stars
A multiple-shell red giant
Stellar Evolution
38. Learn about It!
Elements heavier than iron are formed after a supernova
1. An exploding multiple-shell red giant is called a supernova
• Happens when its core can no longer produce energy to
resist gravity
2. It releases massive quantities of high-energy neutrinos
• Neutrinos break nucleons and release neutrons
3. The generated neutrons are picked up by nearby stars
• Key step in the formation of elements heavier than iron
Stellar Evolution
39. Learn about It!
1. The discovery of interstellar gas and dust in the early 1900s
2. The study of different stages of stellar evolution happening
throughout the universe
• Infrared radiation (IR) can be detected from different
stages of stellar evolution
• IR released by protostar is measured and compared to
IR from nearby area with zero extinction
• Approximation of energy, temperature and pressure
from IR
Proving Stellar Evolution and Nucleosynthesis
40. Key Points
Stellar nucleosynthesis is the process by which elements
are formed within stars.
1
The star formation theory proposes that stars form due
to the collapse of the dense regions of a molecular cloud.
2
Stellar evolution is the process by which a star changes
during its lifetime.
3
41. Key Points
Stellar nucleosynthesis is the process by which elements
are formed in the cores and overlying layers of the stars
through nuclear fusion reactions.
1
Hydrogen burning is a set of stellar processes that
produce energy in the stars.
2
Helium burning is a set of stellar nuclear reactions that
uses helium to produce heavier elements such as
beryllium, oxygen, neon and iron.
3
43. Learn about It!
Neutron capture starts with a neutron being added to a seed
nucleus
This starting reaction would then produce a heavier isotope of
the element
If this isotope is unstable, it would undergo beta decay
Neutron Capture
44. Learn about It!
Beta decay results in an increase in the number of protons of
the nucleus by one
A heavier nucleus of a new element is formed
Neutron Capture
45. Learn about It!
Proton capture or p-process starts with the addition of a p to
a nucleus after a supernova is formed
The tremendous amount of energy available allows the
addition of a p to the nucleus
Usually not favorable because of Coulombic repulsion
Proton Capture
46. Learn about It!
Proton capture or p-process starts with the addition of a p to
a nucleus after a supernova is formed
Produces a heavier nucleus that is different from the seed
nucleus
Proton Capture
49. Key Points
Stellar nucleosynthesis fusion reactions cannot
produce nuclei higher than iron. Synthesis of heavier
nuclei happens via neutron or proton capture
processes.
1
In neutron capture, a neutron is added to a seed
nucleus. The addition of neutron produces a heavier
isotope of the element. Neutron capture can occur
slowly or rapidly.
2
50. Key Points
Beta decay results in an increase in the number of
protons of the nucleus by one. Hence, a heavier
nucleus is formed.
3
Proton capture or p-process is the addition of a
proton in the nucleus.
4
