The Universe
Galaxy Formation
and Evolution
Galaxies are believed to have formed from mergers of
smaller galaxies and star clusters.
Galaxy Collisions
The separation between galaxies is usually not large
compared to the size of the galaxies themselves, and
galactic collisions are frequent.
The “cartwheel” galaxy on
the left appears to be the
result of a head-on collision
with another galaxy,
perhaps one of those on the
right.
Galaxy Collisions
This galaxy collision has led to bursts of star formation in both
galaxies; ultimately they will probably merge.
The Milky Way Galaxy also contains stars in its
halo that appear to have been the result of the
capture of smaller galaxies. The smaller galaxy
dissolves within the larger one, a case of the
littler one being “digested,” much as other dwarf
companion galaxies were probably “consumed”
by our Galaxy long ago.
Mergers of two
spiral galaxies
probably result in
an elliptical galaxy;
the merger of a
spiral galaxy and a
dwarf galaxy
probably results in
a larger spiral
galaxy.
How big is big?
The size of the Universe
http://htwins.net/scale2/
http://www.youtube.com/watch?v=HEheh1B
H34Q&feature=related
Extra credit: Make your own how big is big
video or game or demo!!!
Big Bang
According to the Big Bang model, the
universe was originally in an extremely hot
and dense state that expanded rapidly. As
it expanded, it cooled and continues to
expand today.
Big Bang Theory
• Occurred about 15 Billion years ago
• Started as a primordial atom- an infinitely
small space
• Exploded in a a burst of energy
• Small super dense hot universe
• Over time it cooled and expanded away
The Expanding Universe
If this expansion is extrapolated backward in time, all
galaxies are seen to originate from a single point in an
event called the Big Bang.
So, where was the Big Bang?
It was everywhere!
There is no center of the universe!!!
Wooooooo……
You are the center of the
Universe
http://www.youtube.com/watch?v=DsXsJtO
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26.2 The Expanding Universe
This can be demonstrated in two dimensions. Imagine a
balloon with coins stuck to it. As we blow up the balloon,
the coins all move farther and farther apart. There is, on
the surface of the balloon, no “center” of expansion.
Big Bang Model
• Follow the instructions on the lab sheet to
model the expansion of the Universe
The Expanding Universe
The same analogy can be used to explain the cosmological
redshift
The Expanding Universe
If the universe is
homogeneous, isotropic
(the same in every
direction), infinite, and
unchanging, the entire sky
should be as bright as the
surface of the Sun. So why
is it dark?
A contradiction known as
Olber’s paradox
Ober’s Paradox
http://www.youtube.com/watch?v=yQz0Vg
MNGPQ
http://www.youtube.com/watch?v=gxJ4M7t
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Observation
Almost all galaxies are red-shifted.
The most distant galaxies exhibit the greatest
red-shift.
The ratio of recessional velocity to distance is
between 50 and 100 km/s per kiloparsec and is
called the Hubble Constant.
The Cosmic Background Explorer (COBE) found
that the temperature of intergalactic space was
not zero.
Inference
Observation
Inference
Almost all galaxies are red-shifted.
Almost all galaxies are moving away from the
Milky Way.
The most distant galaxies exhibit the greatest
red-shift.
The most distant galaxies are moving away
the fastest.
The Universe has been expanding for 8 to 15
The ratio of recessional velocity to distance is
billion years.
between 50 and 100 km/s per kiloparsec and is
called the Hubble Constant.
The universe has not yet cooled from the
The Cosmic Background Explorer (COBE) found rapid Big Bang expansion.
that the temperature of intergalactic space was
not zero.
The Fate of the Cosmos
There are two possibilities for the Universe in the far future:
1. It could keep expanding forever.
2. It could collapse.
Assuming that the only relevant force is gravity, which way
the Universe goes depends on its density.
The Fate of the Cosmos
If the density is low, the universe will expand forever. If it is
high, the universe will ultimately collapse.
Dark Energy
Dark Energy vs. Dark Matter
While dark energy repels, dark
matter attracts. And dark
matter’s influence shows up
even in individual galaxies,
while dark energy acts only on
the scale of the entire
universe
Dark energy
The Universe is full of matter and gravity pulls all this matter together.
The Hubble Space Telescope (HST) in 1998 observed a very distant
supernovae showing that the Universe was actually expanding more
slowly than it is today. Expansion of the universe is accelerating!
Roughly 68% of the Universe is dark energy, 27% is Dark matter. 5% is
“normal “ matter
We do not have a good explanation of dark energy yet.
Dark Matter
Matter that influences the evolution of the universe
gravitationally, but is not seen directly in our present
observations. It neither emits or absorbs light.
About one-quarter of the universe consists of dark
matter, which releases no detectable energy, but
which exerts a gravitational pull on all the visible
matter in the universe.
http://science.nasa.gov/science-news/science-at-nasa/2013/14apr_ams/
Good resource for further information:
http://science.nasa.gov/astrophysics/focus-areas/what-is-dark-energy/
The Milky Way is shaped like a disk that is about
100,000 light-years across. The stars in this disk all
orbit the center of the galaxy. The laws of gravity say
that the stars that are closest to the center of the
galaxy — which is also its center of mass — should
move faster than those out on the galaxy’s edge.
Yet when astronomers measured stars all across the
galaxy, they found that they all orbit the center of the
galaxy at about the same speed. This suggests that
something outside the galaxy’s disk is tugging at the
stars: dark matter.
Dark Matter and the Milky Way
Calculations show that a
vast "halo" of dark matter
surrounds the Milky Way.
The halo may be 10 times
as massive as the bright
disk, so it exerts a strong
gravitational pull.
Video on Dark matter
http://www.youtube.com/watch?v=rLmcbjL
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http://www.youtube.com/watch?v=fQLKS6
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