Download Big Bang

final exam!!!
 Today we will discuss Cosmology and the Big
Bang
 Wednesday we will finish the Big Bang, have a
short discussion of Life in the Universe, and
review for the final exam
 Remember:
AST 1002
Planets, Stars and Galaxies
Expanding Universe
Today’s Lecture: purpose & goals
1)
2)
3)
4)
5)
Hubble’s Law
Expanding Universe
Cosmology Assumptions
The Origin of the Universe
“the Big Bang”
Fate of the Universe
“the Great Wall”
Virgo
Cluster
Earth
Looking at an ‘empty patch of sky
Galactic Clusters – II
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SuperClusters
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On even greater scales the galaxy clusters themselves form
clusters called superclusters that can be tens to hundreds
of millions of light years across.
These superclusters resemble
Virgo III
“…the froth on soap bubbles…”
group
in space.
10 million ly
Between them lie great voids
containing relatively few galaxies.
Virgo
Cluster
Sculptor
Local
Group
Canes
group
Leo I
Fornax
Cluster
Ursa Major
group
Leo II
group
Galaxy Collisions
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Occasionally galaxies collide
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Passage of one galaxy through/near
another causes major “stirring”
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Happens most often in centers of rich
galactic clusters
Stars that make up the galaxies don’t
actually slam into each other
due to gravitational interaction
Causes new activity such as
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huge burst of
star formation,
creation of
AGNs,…
Think of walking around
before or after a football game
Review
Pop II
Pop II
Pop I
slow rotation
very little gas and dust
no new star formation!!
fast rotation
significant gas and dust – in arms
significant new star formation!!
(in the spiral arms, spherical
component older!!)
small, irregular, no rotation
some gas and dust
some new star formation (randomly
throughout galaxy)
Measuring Distances

Stereoscopic viewing (Parallax)
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only “small” distances
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nearest few thousand stars in our galaxy
“Standard candles”
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objects which have ‘known’ luminosities
Cepheid variables
variation tells luminosity – good to 65-100 million LY
brightest stars in galaxy, size of HII regions, overall brightness of
galaxy – good in steps out to 1-2 billion LY
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Type Ia supernova
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all have same luminosity
good to 8-10 billion LY (a few measured
as far away as 12-13 billion LY)
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Relies on Comparison to examples of the
same type objects in nearby galaxies
History reminder
– “Island Universes”
Andromeda galaxy

1924 – Edwin Hubble
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Measured the distances to
several galaxies using the
Luminosity-Period
relationship of Cepheid
variables, discovered by
Henrietta Leavitt (1912).
(Cepheid variables)
This was conclusive
proof that the galaxy
lay well beyond the
Milky Way.  2 million l.y.
away!
The universe was much larger
than previously thought.
size of the Moon
Andromeda galaxy
Distance Modulus
Formula

Calculate the distance to the Andromeda
Galaxy using Hubble’s method.

m - Mv = -5 + 5log10(d(parsecs))
Luminosity-Period Relation of Cepheid Variables
Galactic Redshifts
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Edwin Hubble (1889-1953) and colleagues
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measured the spectra (light) of many galaxies
found nearly all galaxies are red-shifted
Redshift (Z)
lobserved - lrest
Z=
lrest
From Ch. 2,
(Doppler effect) Z = v/c
(for speeds approaching c,
we’ll need a relativistic version
of this equation.)
Z = [(1+ v/c)/(1+ v/c)]1/2 - 1
Andromeda galaxy
Hubble’s Law
Hubble found the amount of redshift depended upon
the distance

Recessional velocity

the farther away, the greater the redshift
v = H0 x d
Hubble’s data
distance to galaxy
What is H0?
Bigger Structure
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Structure bigger than galaxies
Galaxy groups
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Galaxy clusters
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100s of galaxies – Virgo
Cluster (rich cluster)
Earth
Virgo
Cluster
Superclusters
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2-30 galaxies
Local Group – contains the
Milky Way
groups and clusters combined
The Universe is filled with
large scale structure
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“walls” and “filaments”
separated by great voids – (like
First detailed study done by Margaret Geller & John Hucra,
froth on soap bubbles)
Harvard-Smithsonian Center for Astrophysics
Hubble’s Law
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Holds for essentially all galaxies with measured redshift
and distance
THEREFORE, measuring the redshift tells us the distance
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redshifts up to 95% of the speed of light have been measured!!
 ultraviolet wavelengths can be shifted into the visible, or infrared
H0 is Hubble’s constant = 70 km/(s Mpc)

Mpc = megaparsec
Consequences
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If everything is moving away from us and things farther are
moving faster
Then the Universe is expanding!
This doesn’t mean what you are probably
thinking . . . .
Expanding Universe
Space itself is expanding, not matter flying
apart within space.
Examples:
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dots
rubber band
raisin bread
ants on a balloon
It does not mean we are at the center
of the Universe
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every part of the Universe sees everything
moving away from it
Cosmological Redshift
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We now know 3 kinds of
redshift
Doppler shift
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Gravitational shift
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due to motion
due to distortion of space-time by mass
Cosmological shift
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due to stretching of space
 not due to relative motion
as space stretches, the wavelength stretches
and becomes longer
lobserved - lrest
Z=
lrest
Relativistic (near speed of light):
Non-relativistic (<0.05c):
Z = [(1+ v/c)/(1+ v/c)]1/2 - 1
Z = v/c
Looking Back in Time
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Remember it takes time for light to
reach us
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The farther away, the further back in
time we are looking
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travels at 300,000 km/s
So we see things “as they were” some time
ago
1 billion LY means looking 1 billion years
back in time
So the greater the redshift, the further
back in time
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redshift of 0.1 is 1.4 billion lightyears which
means we are looking 1.4 billion years into
the past
Thinking Back in Time
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If all galaxies are moving away from
each, then in the past all galaxies were
closer to each other.
Going all the way back, it would mean
that everything started out at the
same point
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then began expanding
This starting point is called the Big Bang
We can calculate the age of the
Universe using Hubble’s Law
v = H0 x d 
But
d = v/H0
distance = rate x time

thubble = 1/H0
(the time here is how long the expansion has been
going on  The Age of the Universe)
Big Bang
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At the beginning of our Universe,
all matter was together in a very
compact form
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Then space started expanding
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matter was nothing like it is now
very “hot”
things “cooled”
eventually it was possible for normal
matter to “condense” out of the hooter
form
Big Bang model makes a number of
testable predictions….
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…continued!
At the Beginning
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Originally all the energy (and
matter) of the Universe was
condensed into an incredibly small region
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Energy, matter, space and time were all very different
than today
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MUCH smaller than the size of a proton
need a new “theory of everything” to understand
 not yet possible
 11-dimensional space??? (models are very weird)
During early expansion, space-time and gravity became
separate from energy and mass
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particles and antiparticles were being created from energy and
annihilating into energy all the time
Glow of the Universe
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The early Universe was very
hot and dense
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Eventually the Universe
cooled enough to form hydrogen atoms
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glowed with blackbody
radiation
but so dense the light kept
getting absorbed (opaque)
blackbody radiation could now travel freely
That time called “recombination of the Universe”
Light from that time should be all around us
and be detectable.
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3K background radiation
Cosmic Microwave Background
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(CMB)
This light should be cosmologically
redshifted
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Mostly into microwave region
CMB was first seen in 1960s
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Pensias & Wilson
(Bell Labs)
– won Nobel prize
in physics for this
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twenty years after prediction
COBE satellite mapped the CMB
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measured the spectrum
wonderful match between theory and data
 Temperature = 2.73K
cooled glow from recombination era.
Incredibly uniform across sky.
Composition of Light Elements
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Big Bang model predicts the percentage of light
elements
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Hydrogen (1H), deuterium (heavy hydrogen, 2H), helium
(4He), lithium (7Li), beryllium (9Be), boron (10B and 11B),…
elements formed before recombination (created out of
light!)
percentages depend upon density and temperature of
early Universe, and how fast it cooled.
Observed percentages agree with Big Bang model
predictions
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Almost all was created as hydrogen (1H) and helium
(4He), with only trace amounts of anything else.
 must have cooled from
something very hot.
Helium
Fate of the Universe
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The Universe is expanding
But gravity should be pulling it back in
So what should the Universe’s fate be:
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Continue expanding forever
Have expansion keep getting slower forever and stop at infinite
time
Expansion stops and eventually Universe collapses upon itself
These possibilities are called
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open universe
flat universe
closed universe
Enough Matter?
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The amount of matter in the Universe helps determine its
fate
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if there is enough mass, gravity wins
given H0 = 70 km/(s Mpc), critical mass density is 8x10-27 kg/m3
define MASS as the actual density of mass in the Universe
divided by the critical density
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MASS < 1 is an open universe
MASS = 1 is a flat universe
MASS > 1 is a closed universe
Enough Matter?
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Visible matter (stars in galaxies, & hot gas)
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Dark matter in galaxies
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only 2% of critical density; MASS = 0.02
(measured by galaxy rotation curves)
about 10 times as much; MASS = 0.2
Dark matter between galaxies
(measured by watching galaxies fall
inward in galactic clusters and
from gravitational lensing)
 raises total to 30% of critical density
 MASS = 0.3
We do not observe enough matter to cause
the Universe to be closed
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But it’s not the end of the story…
Is the Expansion Slowing Down?
Use Type 1a supernovae
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a standard candle
use brightness to determine
distance
use redshift to determine speed
compare them
data lies below prediction (galaxies
are speeding up!!)
Answer: Strangely enough…
the rate of expansion is speeding up!
Formation of Structure
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(early in the Universe)
Normal matter was spread fairly
evenly
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Dark matter was not distributed
smoothly
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clumps remained
Expansion spread things out
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due to interactions and radiation
but gravity held large clumps of dark matter
together
Dark matter attracted normal matter
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source of galaxies and structure