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The Universe
Chapter 20
“Recognize that the very molecules that make
up your body, the atoms that construct the molecules,
are traceable to the crucibles that were once the
centers of high mass stars that exploded their
chemically rich guts into the galaxy, enriching pristine
gas clouds with the chemistry of life. So that we are all
connected to each other biologically, to the earth
chemically and to the rest of the universe
atomically…It’s not that we are better than the
universe, we are part of the universe. We are in the
universe and the universe is in us.”
- Neil deGrasse Tyson
HUNTING THE EDGE OF SPACE
What are Stars?
3
What are Stars?
• The warthog was right…
• Stars: huge sphere of very
hot gas that emits light and
other radiation
• Formed from clouds of
dust and gas, or nebulas,
and go through different
stages as they age
4
Light Years
• Stars are located at various distances from the
Earth
• We measure this distance in light-years (ly)
• Distance light travels in one year - 9.5 × 1012 km
• UNIT OF DISTANCE, it would take us 10 million years to
“drive” 1 light year
5
Stars are powered by nuclear
fusion reactions
• Remember: fusion is the combining of hydrogen in the
creation of helium
• A star is held together by the huge gravitational force
created by its own mass
• Because of this, the pressure INSIDE the star is immense
(1billion times that of earths atmosphere)
• The temperature of the core is more than 15 million
Kelvins
• http://www.youtube.com/watch?v=qe7mbv7v9Zg
Studying Stars
• Ancient Greeks classified
stars by their color and
brightness
 Telescopes allowed
astronomers to study
stars in more detail for the
first time
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Energy moves slowly through the
layers of a star
• Energy moves
through the layers of
the stars through a
combination of
radiation and
convection.
• Convection: hot gas moves away from the star’s
core
• Radiation: energy is transferred to individual
atoms; the atoms absorb the energy and transfer
it to other atoms in random directions; atoms
near the surface give off the energy into space as
electromagnetic radiation
Studying Stars
• Ancient Greeks:
classified stars by
their color and
brightness
• Telescopes
allowed
astronomers to
study stars in
more detail for
the first time
Traits of stars
• Depends on the star’s temperature, size, and
distance from the Earth.
• Stars produce energy in different wavelengths of
electromagnetic radiation other than visible light
like high energy X rays and low energy radio
waves
Traits of stars continued
• A star’s color is related to its temperature: hotter
objects glow with colors that are more intense
with shorter wavelengths (toward the blue end);
cooler colors have longer wavelengths closer to
red
• The color that we see when we look directly at a
hot object is determined mainly by the wavelength
at which the object emits the most light
• The sun appears yellow because that is the
wavelength of light it releases the most of
Spectral lines reveal the composition
of stars
• Light can be separated into a spectrum (like a
rainbow shows all the colors)
• When you pass light through a spectrograph it
makes a unique pattern
• The pattern is determined by what types of
elements make up the gas that are emitted from
the light
• So each element has its own unique “fingerprint”
when passed through this fancy prism
• Comparing the known “fingerprints” to what
gases the star emits will give the make up of a
star
Life Cycle of Stars
• Like all things, stars have a natural progression from
birth, through development, and then death
• About 90% of the stars in our galaxy, including the
sun, are around midlife
• They are converting hydrogen into helium in their
interiors (with nuclear fusion!).
16
Life Cycle of Stars
• Nebula: thin cloud of gas and
dust
• Gravity causes nebula to
collapse inward and begin
spinning – creating a protostar
• Hydrogen atoms begin fusing
into Helium
17
Life Cycle of Stars
• The onset of this fusion marks the
birth of a star
• Hydrostatic Equilibrium: The fusion
reactions in the core of the sun
produce energy and outward
pressure, this balances the inward
pressure from gravity
• This creates the round shape of the
sun
18
The sun will become a red giant before
it dies
• When all of the Sun's core supply of Hydrogen
has been converted into Helium, nuclear fusion
will stop.
• With no outward pressure, gravity will crush the
core smaller and smaller.
• The pressure and temperature becomes so great
that Helium is converted into Carbon and
oxygen.
Life Cycle of Stars
• A star that is stable, like our sun, is
called a Main Sequence Star
• When the sun’s supply of hydrogen runs
out, it begins to fuse heavier elements,
all the way up to iron
• The outer layers of dust and gas expand,
and the star swells to a Red Giant – a
large reddish star in its late life cycle
20
• When the core depletes the helium, it will get
smaller again, but cause the outer layer of the
star to expand
• The Sun's outer photosphere expands to
tremendous size, engulfing Mercury, Venus, and
perhaps even Earth and Mars.
Life Cycle of Stars
• The outer layers eject themselves as a planetary
nebula
• In the sun’s case, these layers will engulf Mercury,
Venus, and possibly Earth and Mars
• The remaining core will shrink to an Earth-size ball
– called a White Dwarf
22
• The formation of an
iron core signals the
death of a supergiant
star
• Why? It requires more
energy to fuse heavier
elements rather than
releasing it so THE
INWARD FORCE IS
GREATER THAT THE
OUTWARD FORCE
Life Cycle of Stars
• Stars larger than the sun will
become supernovas
• Supernova: a stellar explosion
• The collapse of the core
rebounds with a shock wave that
violently blows the star’s outer
layers away from the core.
• A supernova can become a black
hole or a neutron star
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Life Cycle of Stars
• A black hole consists of matter
so massive and compressed that
nothing can escape its
gravitational pull, not even light.
• The only way to detect one is by
observing the radiation of light
and X rays from the objects that
revolve rapidly around them
25
Traits of Stars
• Spectral lines reveal the composition of stars
• When you pass light through a spectrograph, it
makes a unique pattern
• The pattern is determined by what types of elements
make up the gas emitted from the light
• Each element has its own unique “fingerprint”
when passed through this fancy prism and
comparing these will give the make up of a star
26
H-R Diagram
(Hertzprung Russel)
• Diagram that shows how stars evolve
• This diagram doesn’t show where stars are literally,
only their progression as they age
• Y-axis (vertical): luminosity, or the brightness of stars.
• X-axis (horizontal): surface temperature of the stars, with
hotter temperatures on the left side
• Once a star is stable it appears on a dotted line on the H-R
diagram called the main sequence.
27
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The Milky Way and
Other Galaxies
Section 2
29
Galaxies
• Galaxy: a collection of millions to
billions of stars
• Grouped in clusters
• The Milky Way and the Adromeda
galaxy are two of the largest, with
a cluster of more than 30 galaxies
• Gravity holds galaxies together
in space, and the solar system
revolves around the center of
the galaxy because of this
gravity
30
Galaxies
• Superclusters contain
thousands of galaxies
• They are the largest
known structures in the
universe
• It takes our solar system
about 226 million years
to complete one orbit of
our galaxy
31
Galaxies
• Can be divided into three
main types:
• Spiral, Elliptical, and
Irregular
• Each has many stars, but
differs in structure
32
Spiral Galaxies
• Spiral arms made of gas,
dust, and stars
• Always growing with many
new stars.
• Milky Way
• Has a lot of interstellar
matter –
• the medium needed to
create new stars, mostly
gas and dust
33
Elliptical Galaxies
• Little gas or dust, no
spiral arms– plainly
round
• Spherical or egg
shaped
• Often reddish in
color
34
Irregular Galaxies
• Lack regular shapes and well
defined structures
• Some have little interstellar
matter while others have a lot
• Young stars are hot
• Gravity can be some of the
cause of the irregular shape
35
Quasars may be infant galaxies
• Quasi- stellar object
named for its star-like
appearance
• They are the most
distant and most
radiant object in
space
• Might be the central
parts of distant
galaxies seen as they
were when very
young
Galaxies Over Time
• When a scientist observes a galaxy that is 1 billion years away,
they are observing light that left the galaxy 1 billion years ago
• Scientists don’t know what the galaxy looks like now, but can
study similar closer galaxies to piece together the evolution of
galaxies
• The gas, dust and stars that make up galaxies is in constant
motion, as they consume their gas/dust they can no longer make
stars
• Gravity changes the shapes of galaxies
• The gas/dust from nearby galaxies can collide and set off rapid
burst of new star formation
37
Origin of the Universe
Section 3
38
The Universe
• Universe: consists of all space, matter and energy
that exists- now, in the past or in the future
• Since distances are so far we use large units to
express the distances between objects.
• It takes time for light to travel in space
• We see the universe now as it was in the past
• The farther an object is, the older the light that we
get from that object is
• The sun is 8 light minutes away, that means we are seeing
what the sun looked like 8 minutes ago
39
The Universe
• Most of the universe is
empty space
• Space is a vacuum with
no air and no air
pressure
40
What happened at the beginning?
• Scientists use telescopes to study the ancient
light emitted by stars
• Scientists have theorized that the universe
formed during a cataclysmic event known as the
big bang
Edwin Hubble
• 1929: Announced the universe is expanding based on
observations of spectral lines in the light from other
galaxies
• He found these lines were almost always shifted
toward the red end of the spectrum
• THE SHIFTS showed the universe was expanding!
42
• Doppler effect: a change in the observed frequency of
electromagnetic radiation when an object or observer is moving
• Something moving closer to you appears to have a shorter
wavelength (blue shift)
• Something moving further away appears to have a longer
wavelength (red shift)
Edwin Hubble
• The red shift can be
explained by the Doppler
Effect
• Light waves from an object
moving away would be
stretched out
• The faster the object
moves, the longer the
wavelength
44
The Big Bang
• Scientists use telescopes to study the ancient light
emitted by stars
• Scientists have theorized that the universe formed
during a cataclysmic event known as the big bang
• The Big Bang Theory: States that the world began
with a giant explosion 13 billion to 15 billion years ago
(universe is believed to be about 13.7 billion years
ago)
45
Cosmic Background Radiation
• 1965: Arno Penzias and Robert Wilson were making
adjustments to a radio antenna they built
• There was a steady but dim signal they kept
intercepting
• They realized it was cosmic background radiation
• The detected microwaves are remnants of radiation
produced by the Big Bang
46
The Big Bang
• According to this theory, before the big bang
there was:
• Nothing
• No time
• No space
• But out of this big nothing came the vast system
of space, time, matter, and pure energy that now
makes up the universe
47
The Big Bang
• According to the Big Bang Theory:
• Immediately after, the universe was extremely hot and
made up of pure energy
• There was a period of rapid expansion that caused the
energy to cool, and allowed electrons, neutrons and
protons to form
• Hydrogen nuclei started to form but it was still too hot for
atoms to be stable
• About 380,000 years after the big bang is when electrons
could combine with atomic nuclei to form atoms
• The first stars were born about 400 million years after the
big bang
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The Big Bang
• There are several theories being tested, and as
new information is found, we might revise what
we believe
• The Big Bang is the most supported by current
evidence
• cosmic background radiation and observation of the
movement of distant galaxies
50
Future of the Universe
• The future of the universe is uncertain
• The universe is still expanding but it will not do this
forever
• The combined gravity of all the mass in the universe is
also pulling the universe inward
51
Future of the Universe
• Possible outcomes:
• 1. the universe will keep
expanding forever
• 2. the expansion of the
universe will gradually slow
down and the universe will
approach a limit in size
• 3. The universe will stop
expanding and start to fall
back on itself
52
Future of the Universe
• If there isn’t enough mass – gravity will not be strong
enough to stop the expansion
• Just right amount of mass – the expansion will slow
down but not end completely
• Too much mass – gravity will overcome the
expansion and the universe will start to contract (the
big crunch), becoming very hot and small, at this
point the universe could end, or they cycle would
start again
53
• It is possible that with too much mass the
collapsing would become very hot and very small
• Causing either the end
• Or another big bang to happen
• New technology helps scientists and
astronomers test theories of the size of the
universe
• There is debate about dark matter (matter that is
not visible)
Planets, black holes, brown dwarfs
• Dark matter contains dark energy– how do we even
begin to observe this?
• https://www.youtube.com/watch?v=QAa2O_8wBUQ
 Scientist use mathematics to build better models
• Einstein expanded on Newton’s theory of gravity
• Mass curves space (like your body curves a mattress if
you sit in the bed)
• In 1919 a total solar eclipse showed that stars (LIGHT)
that could only be seen during the eclipse were in
slightly different positions than expected
• The larger the mass, the more distortion
• Solar Eclipse