Download Expansion of the Universe

THE UNIVERSE
Integrated Science I
WHAT IS THE BIG BANG THEORY?
The Big Bang Model the most widely accepted theory for
the start of our universe
It hypothesizes that the universe began 12 to 14 billion years
ago
At that time, the entire Universe was inside
a bubble that was thousands of times smaller
than a pinhead. It was hotter and denser than
anything we can imagine
CONTINUED…
 Then it suddenly exploded – the Universe that we know was
born!
 Time, space and matter all began with the Big Bang. In a
fraction of a second, the Universe grew from smaller than a
single atom to bigger than a galaxy and it kept on growing at a
fantastic rate
It is still expanding today
After the big bang, the universe expanded quickly (and
continues to expand) and then cooled down enough for atoms
to form.
Gravity pulled the atoms together into gas clouds that
eventually became stars, which comprise young galaxies
HOW DO WE KNOW THE UNIVERSE
IS EXPANDING?
Remember this!!?!
The Doppler Effect! It isn’t
going away…
HOW DOES THE DOPPLER EFFECT
RELATE TO THE UNIVERSE EXPANDING?
Stars and galaxies are not getting bigger; rather, the space
between all objects is expanding with time
The expansion of the universe was discovered
in 1929, by American astronomer Edwin Hubble
When Edwin Hubble, the astronomer for whom the
Hubble Space Telescope is named, measured the
spectrum of distant stars and galaxies, he observed
extra amounts of red light (red shifting).
WHAT IS THE RED SHIFT?
Red shift occurs when a light-emitting body moves away
from us. Light waves traveling in front of a body bunch up as
it travels; light waves at the trailing end stretch out. The
stretched-out light waves are said to be red shifting. Hubble
concluded that the red shift means the stars and galaxies
are actually moving away, which led him to develop the
theory of an expanding universe.
EXPANSION OF THE UNIVERSE
 Proven by the Doppler
shift
•
•
Starlight moving towards
Earth is bluish
Starlight moving away
from Earth is reddish
 All galaxies outside the
our galaxy indicate a
red shift – therefore they
are moving away from
us
GALAXIES
A galaxy is a group of billions of individual stars, star
systems, star clusters, dust and gas (hydrogen and
helium) bound together by gravity
There are billions of galaxies in the universe, and
they are classified by size and shape
• Earth is in the Milky Way galaxy
∙ There are about 200 billion stars in the Milky Way
∙ 100,000 light years wide!
DIFFERENT TYPES OF GALAXIES
 There are 3 types of galaxies: elliptical, spiral, and irregular
• Elliptical
∙ Most common type of galaxy
∙ Shaped like large, 3-D ellipse (looks like a football)
• Spiral (like the Milky Way) – have spiral arms that wind out,
youngest stars at the center of the spiral
∙ Normal – arms start close to center
∙ Barred – arms extend from a large bar
• Irregular – many different shapes
∙ Smaller and less common
STARS
When heated to a sufficiently high temperature by
gravitational attraction, stars begin nuclear reactions
(NUCLEAR FUSION!), which convert matter to energy and
fuse the lighter elements into heavier ones
These and other fusion processes in stars have led to the
formation of all the other elements (heavier ones than
Hydrogen and Helium)
All of the elements, except for hydrogen and helium,
originated from the nuclear fusion reactions of stars
LIFETIME OF A STAR
The overall lifespan of a star is determined by its mass
Stars spend roughly 90% of their lives burning hydrogen into
helium on the main sequence
Massive stars need higher central temperatures and
pressures to support themselves against gravitational
collapse, and for this reason, fusion reactions in these stars
proceed at a faster rate than in lower mass stars
IMPORTANT: The result is that massive stars use up their core
hydrogen fuel rapidly and spend less time on the main
sequence before evolving into a red giant star.
HOW TO CLASSIFY STARS
Stars are classified by their color, size, luminosity and mass
A Hertzprung-Russell (H-R) diagram must be used to
estimate the sizes of stars and predict how stars will evolve
Most stars fall on the main sequence of the H-R diagram
• A diagonal band running from the bright hot stars on the
upper left to the dim cool stars on the lower right
HERTZSPRUNG-RUSSELL DIAGRAM
Brightness
Supergiants
Main
Sequence
Giants
White Dwarfs
Temperature
Where is
our Sun?
-Main
Sequence
LIFETIME OF A STAR
I.
When hydrogen fuel is used up, nuclear fusion can no longer occur
and the star begins to “die”
II. Stages of a Low-mass star’s life:
A. Nebula – star beginning, a cloud of gas and dust condense
together
B. Main Sequence – fusion causes pressure that is balanced
-A star’s mass determines the star’s place on the main sequence and how
long it will stay there
C. Giant – when hydrogen is exhausted, a balance no longer exists,
star expands and cools
D. White Dwarf – after core uses up helium, expands more and outer
layers escape into space, leaving a very hot, dense core (about
the size of Earth)
** If the star is a high-mass star, it could become a black hole