Transcript Cosmology- the study of the origin, evolution and composition of the universe.

Cosmology- the study of
the origin, evolution and
composition of the universe

Big Bang Theory (1940s)-
universe violently exploded into
being about 13-15 billion years ago
– Was an expansion of
space that brought matter
along with it
http://www.globalchange.umich.ed
u/globalchange1/current/lectures/
universe/universe.html
Evidence for the Big Bang
1.
Red Shift- Measurements of the red
shifts of virtually all galaxies (except a
few) show that the visible universe is
expanding in all directions.
http://www.globalchange.umich.edu/globalchange1/current/lectures/universe/universe.html
The Expanding Universe!

In 1929, Edwin Hubble (yes, that Hubble)
measured red shifts and distances of
galaxies
– Found that the farther from Earth a galaxy is,
the faster it is moving away from us
– All points are moving away from all other
points, and no one point is at the center
– Hubble’s Law: v = Hd
Hubble’s Law
Hubble’s Law: v = Hd
V = velocity (km/s)
H = Hubble constant
(usually 65-73 km/sec/Mpc)
D = distance from Earth (Mpc)
Evidence for an expanding universe
The spectrum of hydrogen gas is the unique
fingerprint of that element
Hydrogen lamp
Evidence for an expanding universe
When we see a repeat of the pattern we saw in
the lab, we know hydrogen is present
Orion Nebula
Evidence for an expanding universe
We see the same repeating pattern of lines in
a galaxy, but displaced to the red
Galaxy UGC 12915
Evidence for an expanding universe
The further the galaxy,
the more the shift to the red
Galaxy UGC 12508
Evidence for an expanding universe
The greater the red shift,
the faster the galaxy is receding
Galaxy KUG 1750
Evidence for an expanding universe
The red shift is caused
by the expansion of space.
Galaxy KUG 1217
Evidence for an expanding universe
The red shift is evidence
for an expanding universe
Galaxy IRAS F09159
2. Cosmic background radiation-visible universe is permeated by "cosmic
background" microwave radiation, coming
from all directions
-it’s the red-shifted remnant of the
radiation left over from the original Big
Bang
-Initial Bang would have sent out strong
shortwave radiation (up to trillions of
degrees) in all directions
More on cosmic background radiation
-Over time, radiation would spread out and
cool; filling the universe
-Would now strike Earth as microwave
radiation only a few degrees above
absolute zero
(-270°C, or 3K)
-Radiation mapped by COBE and WMAP
observatories
COBE- Cosmic Background
Explorer Mission
WMAP- Wilkinson Microwave
Anisotropy Probe
3. Universe is mostly H and He

Prediction: A hot, dense expanding
universe, should be predominantly
hydrogen, helium (lighter elements)

Observation: Universe is
~75% hydrogen and
~25% helium by mass
4. Galaxies look different over time
Prediction: An expanding universe is
evolving over time. If we look at the early
universe, it should appear different.
 Observation: Distant galaxies
less evolved, physically
and chemically.

What’s the Fate of the Universe?
The outward momentum of the expanding
universe is opposed by the inward pull of
gravity- Which force is stronger???
3 scenarios:
1. Open universe- continual, slowed
expansion (“Big Chill”) or continual, sped
up expansion (“Big Rip”)
2. Closed universe (“Big Crunch”)expansion will turn into a contraction
3. Flat universe- expansion will slow
down and eventually stop
some cool info
So… What will happen?

Answer depends on the total amount of
matter in the universe (expressed as the
average density of matter)
– Average density can be observed by
astronomers
– It includes light and dark matter

Compare average density to critical
density (the dividing point between open
or closed universe; about 10-26 kg/m3)
If average density = critical density, then
the universe is flat
 If average density < critical density, then
the universe is open
 If average density > critical density, then
the universe is closed
SO FAR- astronomers favor the open model
ALSO- data suggests that rate of expansion
is speeding up…is dark energy pushing
the universe apart?

What does our galaxy look like?

The Milky Way
The Milky Way- a Spiral Galaxy!
It takes our sun about 225-250 million years to complete
one journey around the galactic center at a speed of
800,000 km/hr. This is called a “cosmic year”.
Galaxy Shapes
Galaxy Groups
Galaxies are often part of larger groups of
galaxies
 The Milky Way
is one of about
40 galaxies in
our Local Group

And now for some weird galactic stuff
Quasars- quasi-stellar radio sources
 Exist at the nuclei of very distant active
galaxies; very high red shifts
 emit visible light, radio waves, infrared, xrays, even gamma rays
 Most luminous objects in the universe
 Formed by material that builds up on the
accretion disk of a supermassive back
hole

http://starchild.
gsfc.nasa.gov
-quasars (QSOs) give off more energy than
100 galaxies combined!
-the most distant objects in the universe
-get energy from black holes at centers of
their galaxies
Active galaxy
at center of
Centaurus A