Humans are inherently curious
about their place in the Universe
We live in an Island Universe
A Spiral Galaxy seen edge on.
Our galaxy and others are collections of stars of all ages. The birth
and death of stars is an ongoing process. Stars are formed by the
gravitational collapse of interstellar gas and dust.
The Sombrero Galaxy
The Andromeda Galaxy - our twin at a
distance of 2.2 million light-years.
• Motion of stars in the outer region of our
galaxy shows that mass of know matter
(stars, IM, etc.) is less than 10% of the mass
of the Galaxy.
• Motion of other galaxies within clusters
shows need for dark matter.
• Best guess for form of dark matter: exotic
The Rosetta Nebula - hot, glowing hydrogen gas
surrounding a cluster of young, hot stars.
The Horsehead Nebula
The Orion Nebula - one of
the maternity wards of the
galaxy. New stars are
forming from interstellar
gas and dust.
Hubble photo of the star forming region in the Eagle Nebula
The Jewel Box - a young cluster of stars
Evolution of a 1 solar mass star
Protostar - core not hot
enough for fusion.
Main sequence - hydrogen
fuses to helium in the core.
Red giant - fusion in a shell
surrounding the core. More
energy is being generated.
Star swells up and cools.
Ejects outer regions.
White dwarf -dead star, no
fusion. It is just cooling off.
The Death of a 1 Solar Mass Star
Near the end of its life
the star will develop a
carbon and oxygen core.
The core will not get
hot enough to fuse
The star will pulsate
unstably and will
eject its outer envelop
leaving behind a dead
star that will become
a white dwarf.
The Ring Nebula - when a star like our sun dies it ejects
its outer regions. A dead white dwarf star is left behind.
The Death of a 15 Solar Mass Star
Near the end of its life
the star will develop
and iron core.
Reactions in the iron
core will cause the star
to explode (supernova)
scattering its contents
into interstellar space.
A dead neutron star
will be left behind.
Elements heavier than
iron will be created in
Crab Nebula -- supernova explosion
Massive stars produce the
elements from carbon to iron
through nuclear fusion over
their lifetimes. Supernova
explosions produce elements
heavier than iron and
distribute all these heavier
elements into the interstellar
matter making them available
for later generation stars.
Not only is our galaxy changing with time, the entire Universe is evolving.
The space between us and the distance galaxies is increasing with time.
Hubble’s Law: For distant
galaxies, the redshift in their
radiation (the amount by
which the wavelength of
the radiation is increased)
is directly proportional to
the distance to the galaxy.
Published in 1929.
Edwin Hubble with his
cat Nikolus Copernicus.
(Colliers Magazine, 1949)
Redshift vs distance
Einstein lecturing on the GTR in Pasadena, California, 1932.
Einstein developed the general theory of relativity (GTR) in 1915.
It predicted that space had to be either expanding or contracting.
Einstein believed this to be incorrect and changed his theory.
Expansion of Space
• 1916 - Einstein’s general theory of relativity predicts that
space must be either expanding or contracting. Einstein
does not believe this and tries to “fix” the theory.
• 1920s - Other astronomers and physicists show that all
versions of the GTR require either the expansion or
contraction of space.
• 1929 - Hubble’s Law.
• 1930 - Arthur Eddington explains Hubble’s Law as the
expansion of space as described by the GTR.
• 1930 - Einstein calls his not accepting his original theory
“the greatest blunder of my scientific career.”
The Balloon Model of Expanding Space
Clusters of galaxies are
represented by pieces of
paper on the balloon.
As the balloon is blown
up its surface area (space)
increases with time.
The clusters of galaxies
do not increase in size.
They get further apart but
do not move through
Abbe George LeMaitre
1920s - shows that GTR, even
with the cosmological constant
still requires that space either
expand or contract.
1930s - reenters cosmology.
First to develop a model based
on GTR of what the universe
would have been like in the past.
Father of Big Bang.
Most scientists are skeptical in
part because LeMaitre is a
priest and there are many
similiarites between the Big
Bang and Genesis.
George Gamow 1948 - Gamow used new
knowledge of nuclear physics
along with the GTR to
describe the early universe.
He assumed (like LeMaitre)
that the early universe was
much hotter and denser than
it is today and that the
expansion of space cooled it
and allowed structures to form.
He intended to show how the
hot, dense conditions of the
early universe could produce
all the chemical elements
Gamow with Wolfgang Pauli present in the universe today.
Predictions of the Big Bang
• The early universe contained only hydrogen and helium.
Because of the expansion of space and its cooling effect,
nucleosynthesis only occurred between 3 to 4 minutes after
the big bang (A.B.B.) and essentially stopped after helium.
• The universe is filled with a background radiation whose
temperature is a few degrees above absolute zero. When
neutral atoms formed (about 500,000 yrs A.B.B.), the
electromagnetic radiation essentially stopped interacting
with matter. The expansion of space cooled the radiation
from its initial value of about 3000 K to its present low
Burbidge, Burbidge, Fowler, and
Hoyle show that elements heavier
than helium can be produced in the
interiors of stars. The explosive
deaths of these stars scatter the
elements into the space between the
stars and make them available for
later generation stars (like our sun).
Arno Penzias and Robert Wilson
Early 1960s - Penzias and Wilson
are hired by Bell Labs to evaluate
the performance of the new radio
telescope to be used in trans-Atlantic
They find a small, unexplained
signal regardless of the direction
the telescope is pointed. It is not
enough to be a problem, but they
1964 - They become aware that the
noise in their telescope is the cosmic
background radiation predicted by
the Big Bang theory.
Bell Labs’ radio telescope.
Early History of the Universe
• T = 0 - Big Bang beginning of a hot, dense universe in expanding
space. Expansion cools the universe.
• T = 10-35 sec A.B.B., Temp = 1027 K - Inflationary period. Matter
• Temperature is too hot for any structure to exist. Elementary particles -
leptons (electrons) and quarks in a sea of photons.
• T = 10-5 sec, Temp = 1012 K - Formation of protons and neutrons from
• T = 3 to 4 min, Temp = 109 K - Formation of helium nuclei from
protons and neutrons. 94% protons (H nuclei) and 6% He nuclei.
• T = 300,000 yrs, Temp = 3000 K - Formation of atoms from electrons
and nuclei. Universe becomes neutral and the background radiation is
Outline of the History of the Universe
• The universe began about 15 billion years ago - the big
bang. The early universe was very hot and dense. The
amount of space in the universe increased rapidly with
• The expansion of space cooled the universe and made it
less dense. As a result, about 1 million years after the big
bang, hydrogen and helium atoms formed.
• The force of gravity caused stars and galaxies to form
from the hydrogen and helium gas. Some hydrogen and
helium was not immediately converted to stars but was
left over as interstellar matter.
• The elements heavier than helium were produced by
nuclear reactions in the interiors of stars. Explosions of
dying high-mass stars scattered these elements into
interstellar space and they became part of the interstellar
• Later generations of stars formed from the interstellar
matter. Some had earth-like planets.
• The solar system formed about 4.6 billion years ago.
• Geological, chemical, and biological evolution led to the
present diversity of life on earth.