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Cosmology
Focus Questions:
What are galaxies?
Where do scientists think the
universe came from?
Galaxies and the Universe
The universe is everything
that exists.
The observable universe is
everything we can
observe.
Galaxies and the Universe
Astronomers are not sure
how old the universe is, but
current estimates range from
10-20 billion years.
What are Galaxies?
Galaxies are systems that
contain millions or even
billions of stars.
Most estimates place the
number of galaxies in the
observable universe at 50-100
billion.
What are Galaxies?
Space is so vast that most
galaxies are light years
apart.
What are Galaxies?
We are part of the Milky Way
galaxy. Our star is only one
among hundreds of billions.
The Milky Way galaxy is a
spiral galaxy that is shaped like
a thin disk with a central bulge.
What are Galaxies?
The diameter of the Milky Way
is about 100,000 light-years.
Its greatest thickness is about
10,000 light-years.
The sun is about 26,000 lightyears from the Milky Way’s
center.
What are Galaxies?
The “milky” haze in the night
sky is the large number of
stars that are in this region of
the sky.
What are Galaxies?
Milky Way
What are Galaxies?
•The Milky Way belongs to a
group of more than 30 galaxies
called the Local Group.
•The Milky Way’s nearest
neighbors in the Local Group are
the two Magellanic Clouds, which
can be seen without a telescope
in the Southern Hemisphere.
What are Galaxies?
The Andromeda Galaxy is
faintly visible in the
Northern Hemisphere with
the unaided eye.
Types of Galaxies
No two galaxies
are exactly alike.
Most galaxies can
be classified by
shape.
Tuning Fork Diagram
• Developed by Edwin Hubble
Types of Galaxies
Spiral galaxies (like the Milky Way)
come in a range of types – from
ones with large, bright nuclei of
stars and tightly wound spiral arms,
to ones with very small, dim nuclei
and open sprawling arms.
The Andromeda Galaxy is also a
spiral galaxy.
Types of Galaxies
Some spiral galaxies have a bar
across the central disc and arms
that come off of the bar, not the
nucleus.
These are barred spirals.
Types of Galaxies
Elliptical galaxies range from
nearly spherical to lensshaped.
The galaxy called M87 is an
elliptical galaxy.
Types of Galaxies
Their stars are concentrated in
their centers, and they have no
arms.
Elliptical galaxies contain far less
interstellar gas and dust (than
spiral galaxies), and contain few,
if any, young stars.
Types of Galaxies
Irregular galaxies
have irregular
shapes and are
much smaller and
fainter than both
spiral and elliptical
galaxies.
Types of Galaxies
Stars in irregular galaxies are
spread out unevenly.
The two Magellanic
Clouds are
irregular galaxies.
Origin of the Universe
Scientists cannot say where or
how the universe originated.
However, through observations
and experiments they have put
together a model about how the
universe has developed.
Origin of the Universe
This model is called the Big Bang
model.
The big bang model explains the
history of the universe from a tiny
fraction of a second after it came
into being up to the present time.
A Model of the Beginning
• According to the big bang
model, 10-20 billion years ago
all matter existed in an
incredibly hot and dense state.
• Matter expanded and cooled,
slowly condensing into stars and
galaxies.
A Model of the Beginning
• The first stars consisted
mostly of hydrogen with a
small amount of helium.
• No planets orbited yet,
heavier elements did not yet
exist.
A Model of the Beginning
• More and more stars formed,
matured, and died, making more
and more heavier elements.
• Supernovas and dying red giants
released the heavier elements
into space.
A Model of the Beginning
• Eventually our sun and its 8+
planets were formed from
interstellar gas and dust.
Evidence for the
Big Bang Model
• The distance
between galaxies
and groups of
galaxies seems to
have increased with time (Edwin
Hubble found redshifts in galaxies
he studied).
Evidence
for the
Big Bang
Model
• Cosmic background radiation
has been discovered (radiation
left over from the universe’s
beginning).
Evidence for the Big Bang
Quasars- old
objects at the
edge of the
universe. If
the Big Bang
happened, this
supports it.
Doppler Effect
Is the apparent change in wavelength of light or sound when
an object is moving towards or away from you.
How the Doppler Effect
Works: If a train comes
towards you, its sound
waves get compressed
and get shorter. (You
hear a higher pitch.)
If it moves away from
you, the wavelength gets
longer and you hear a
lower pitch.
Doppler Effect
The Doppler Effect also
applies to light:
If an object in space is
moving toward us, its
wavelength shortens, and the
light shifts towards the blue
end of the color spectrum.
If an object is moving away
fom us, its wavelength gets
longer, and the light shifts
towards the red end of the
color spectrum.
Illustration by Flavio Robles
Fate of the Universe
What shape is the
universe?
"Closed," "open,"
and "flat" actually
refer to the shape,
or curvature, of
space-time itself.
Fate of the Universe
• Open – universe
will expand forever
• Flat – consume all
energy from big
bang, coast to a
halt far in the
future
• Closed – expand
until it reaches
maximum, then
collapsing back on
itself.
HowStuffWorks
Fate of the Universe
A closed universe will lead to a big
CRUNCH
Hubble Telescope
Hubble telescope a
telescope that orbits
the earth outside our
atmosphere.
It provides us with
many of the images
we have of space.
It is an especially
useful telescope
because it does not
have to view things
through our
atmosphere
The
Milky
Way
Our Sun is
just a
small star
in its main
sequence
among
millions of
other stars
in our
galaxy!!!
The Sombrero Galaxy - 28 million light years from Earth was voted best picture taken by the Hubble telescope.
It has 800 billion suns and is 50,000 light years across
The Ant Nebula, a cloud of dust and gas who resembles an ant when
observed using ground-based telescopes. The nebula lies within our
galaxy between 3,000 and 6,000 light years from Earth
This picture is called Eskimo because it looks like a face surrounded by
a furry hood. The hood is, in fact, a ring of comet-shaped objects flying
away from a dying star.
Cat's
Eye
Nebula
The
Hourglass
Nebula,
8,000 light
years away,
has a
pinched-inthe-middle
look because
the winds that
shape it are
weaker at the
center
Cone
Nebula The
part pictured
here is 2.5
light years
in length
(the
equivalent
of 23
million
return trips
to the
Moon)
The Perfect Storm, a small region in the Swan Nebula, 5,500
light years away, described as 'a bubbly ocean of hydrogen and
small amounts of oxygen, sulphur and other elements'
Starry Night, so named because it reminded astronomers of the
Van Gogh painting. It is a halo of light around a star in the
Milky Way
The glowering eyes from 114 million light years away are the
swirling cores of two merging galaxies called NGC 2207 and
IC 2163 in the distant Canis Major constellation
The
Trifid
Nebula. A
'stellar
nursery',
9,000
light years
from here,
it is where
new stars
are being
born
Wrap-Up
What are galaxies?
Where do scientists think
the universe came from?