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Stellar Evolution
An introduction to the beginning of the universe and the
formation of stars.
The Big Bang
The Origin of the
universe is thought
to be from the Big
Bang, which
occurred ~13.9
billion years ago.
Since then, the
universe has been
continually
expanding.
The first stars began
to form around 400
million years after
the Big Bang
Birth of Stars
Nebula are clouds of
dust and gas.
Stellar nebula are
specifically the
beginnings of stars.
As this nebula cloud
(gradually)
increases, the dust
and gas will come
together (collapse)
and eventually form
a star.
The Eagle Nebula “The Pillars of Creation”
(taken via the Hubble Telescope, NASA)
All stars have a life
cycle that begins with
a stellar nebula, but
can lead to different
fates.
Sun-sized stars
evolve along the
main sequence, and
then become red
giants.
More massive stars
become red
supergiants and
eventually end in
supernova
explosions.
Life Cycle of Stars
Summary
The Big Bang occurred ~13.9 billion years ago and the universe has
been expanding ever since.
Stellar nebula are clouds of gas and dust that eventually form stars.
Stars form through the collapse of stellar nebula
The Life Cycle of Stars describes the evolutionary paths for stars.


Low-mass stars eventually become white dwarf stars.
High-mass stars result in supernova.
Nuclear Fusion
The process of the nuclei of atoms fusing together (joining)
to create new atoms
Subatomic Particles
The subatomic particles
combine to form an
atom
Proton:
Positively charged, one
mass unit, located in
nucleus
Neutron
Neutral, one mass unit,
located in nucleus
Electron
Negatively charged, no
mass, located in electron
cloud (surrounding
nucleus)
Basics of an Atomic Nucleus
An atom is defined by
the number of protons it
has in its nucleus
Atomic Mass (A)
Atomic Number:
Number of protons
Atomic Mass:
Sum of neutrons and
protons
1
1
H
Hydrogen Nucleus
Atomic Number: 1
Atomic Mass: 1
Atomic number (Z)
+
Hydrogen Burning
The process of nuclear
fusion occurs in the core
of stars
One kind of nuclear
fusion is also called
hydrogen burning.
It consists of 3 steps.
It requires temperature
of 10 million ºC or
hotter
This process is the
longest stage in a star’s
life
The helium atom is
formed by 2 hydrogen
atoms fusing together
The Helium Atom
Helium is one of the
building blocks of larger
elements
+
4
He
n
+
2
n
Summary
Atoms are made of subatomic particles.

These consist of protons, neutrons and electrons.
An atom is described by its atomic number and atomic mass.
Hydrogen burning is a nuclear fusion process which results in the
formation of helium atoms