Download ASTR 1020 General Astronomy: Stars and Galaxies REVIEW

ASTR 1020
General Astronomy: Stars and Galaxies
REVIEW
Newton’s Laws
• Law #1: A body at rest or in motion
remains that way unless acted upon by an
outside force.
• Law #2: a=F/m
• Law #3: For every action there is an equal
and opposite reaction.
Newton’s Law of Universal Gravitation
Gm1m2
F21 =
r2
Gm1m2
F12 =
r2
(Law #3 Satisfied)
G = 6.7x10-8 dyne.cm2/g2 in cgs units
Value of G is measured. Nobody knows why it is the value it is.
Electrical Force Equation Similar
e1e2
Fe = 2
r
Example
Calculate the period of a planet that is the same distance from the star
Sirius that the Earth is from the Sun.
r=1.5x1013cm
G=6.7x10-8
M=4x1033g
(1.5 x1013 ) 3
4 x1039
13
12
6
7
P = 6.28
=
6
.
3
=
6
.
3
1
.
5
x
10
=
6
.
3
x
15
x
10
=
25
x
10
=
2
.
5
x
10
s
33
26
−8
6.7 x10 x 4 x10
2.5 x10
About 9 Months
Escape Velocity
R
Fall from Large Height
1 2 GMm
mv =
2
R
Same Energy Needed to Reverse and Fly Away
2GM
ve =
R
Escape velocity is the speed
at which object must be thrown
upward to escape and never come
down.
Surface Gravity
Force of Gravity at Surface of Body is
So
GMm
ma =
R2
or
GM
a= 2
R
F=
GMm
R2
The acceleration of a body
near the surface.
Independent of mass.
Remember Galileo and the Leaning Tower of Pisa
Formation of the Solar System
Universe is about 12 Billion Years old (3x1017s)
Milky Way 10 Billion Years old
Sun and Planets – 4.6 Billion Years old
Sun has done about 25 orbits of Milky Way
Stars are being formed all the time -- some young, some old
Stars are formed from clouds of gas
A Star Is Held Up By
Thermal Pressure From Below
Gravity
Outer Mass
Individual Atoms Don’t
Orbit Entire Inside of
Star Like This
They Jostle Each Other
But Effect Is The Same
Temperature Scales
• Fahrenheit –
–
0=salt water freeze 100=human body
• Celsius
–
–
0=pure water freeze 100=water boil (sea level)
C=(F-32)x5/9
• Kelvin
–
–
–
0=absolute zero 100 degrees between freeze and boil
K=C+273
-273C = 0K = Absolute Zero
At Absolute Zero Atoms Stop Moving
The Nuclear Core
Envelope
1 Million K
core
15x106K
Photosphere 5000K At Surface
Cosmic Composition
•
•
•
•
•
H
He
O
C
N
hydrogen
helium
oxygen
carbon
nitrogen
89% by number
11%
0.1%
0.06%
0.015%
Pretty much the composition of the entire universe.
Sun and Jupiter have this composition
Earth does not.
Proton-Proton Chain
Bottom Line: H+H+H+H → He
1
1
1H +1H
→ 1H2 + e+ + ν
2
1
1H +1H
3
3
2He +2He
→ 2He3 + γ
→ 2He4 + 1H1 + 1H1
5x106 < T < 2x107K
CNO Cycle
12
1
6C +1H
13
7N
→ 6C13 + e+ + ν
13
1
6C +1H
14
1
7N +1H
15
8O
→ 7N13 + γ
→ 7N14 + γ
→ 8O15 + γ
→ 7N15 + e+ + ν
15
1
7N +1H
2x107 < T < 108K
→ 6C12 + 2He4
Net: 1H1 +1H1 + 1H1 +1H1 → 2He4 + 2e+ + 4γ +2ν
hydrogen -> helium + energy
Triple-α Reaction
4
4
2He +2He
⇔ 4Be8 + γ
8
4
4Be +2He
→ 6C12 + γ
T < 108K
Must be very dense for this to work
Be8 decays back into helium very quickly
unless struck by another He4
Net: 2He4 +2He4 + 2He4 +2He4 → 6C12 + 2γ
helium -> carbon + energy
Too low density
in Big Bang
Solar Schematic
Sunspot Cycle
During mid 1600’s sunspots became non-existent
Maunder Minimum
Solar Wind 5x105K
Corona 2x106K
Transition Region 105K
Chromosphere 104K
Photosphere 5500K
Star Names
• Arabic Names
– Antares, Capella, Mira, etc.
• Constellations
α Orionis, β Cygni, … then 49 Ori, 50 Ori, etc.
• Catalogues HD80591, SAO 733421, etc
• RA and Dec – just position in the sky
Proper Motion
2003
All stars move
Nearby stars move faster
Appear to move against fixed field
1900
Can Take Many Years
Use Old Photographic Plates
Parallax
I year cycle
The Parsec
1 parsec
1AU
1 arcsecond
360 degrees in circle
60 arcminutes per degree
60 arcseconds per arcminute
200,000AU = 1 parsec = 3x1018cm
parsec ---- parallax second
The Magnitude System
Ptolemy Broke Stars into 5 magnitude groups
m=1 the brightest, m=5 the faintest
In 1700’s it was found this was a logarithmic scale, as that is how
the naked eye responds. Also, faintest were about 100x fainter than
brightest.
Break the factor of 100 into 5 equal factors:
Start with Vega
Polaris 2.51x fainter
2.5x fainter than Polaris
2.5x fainter than that
etc
m=1
m=2
m=3
m=4
1mag = 5 100 = 2.51
Absolute Magnitude
The magnitude a star would have were it at 10pc
We see a star of magnitude m=10 at 100 pc.
What would be its magnitude (M) if it were at 10 pc instead of 100pc?
At 10 times closer the star would be 100x brighter = 5 magnitudes
M = 10-5 = 5
M = m − 5 log10 d + 5
M = 10 − 5 log 100 + 5 = 10 − 10 + 5 = 5
Light Waves
λ
lambda is lower case Greek L
stands for length
Each photon is a sine wave moving at the speed of light
Wavelength is usually measure in Angstroms
1Å = 10-8cm =10-10m
about the diameter of an atom.
Electric and Magnetic
Fields Sloshing Back
And Forth
Parts of EM Spectrum
Radio
Infrared
Visible
Ultraviolet
X-ray
Gamma-ray
λ > 1mm (107A)
1mm> λ > 10000Α
10,000Α > λ > 3500Α
3500Α > λ > 100Α
100A > λ > 0.1A
0.1A > λ
Speed of Light
Speed of Light c = 3x1010cm/s
That’s a very odd statement
2 cars at 65mph
1 car at 130mph
Cover same distance in same amount of time
The Relative speeds are the same
Frequency
λ
λ
λ
λ
Moves λ during each cycle
Frequency is the number of cycles per second,
ν
Moves distance λ for each of ν cycles each second
λν = c
Greek “nu”
Energy of a Photon
ε = hν
h = 6.63x10-27 erg s
Planck’s Constant
ε = 6.6 x10 −27 x6 x1014 = 4 x10 −12 ergs
Sunlight is 107 ergs/cm2/s
energy of yellow photon
Outside we have 1019 photons/cm2/s hit us
Spectroscopy
Spectrum is plot of number of photons as a function of wavelength
Tells us huge amounts about nature of object emitting light.
Thermal Radiation
Planck’s Law
I=
2hc
2
1
λ5 e hc λkT − 1
Temperature Determines Where Spectrum Peaks
Position of Peak Determines Color
Wien’s Law
λ peak
3 x10
=
T
7
Å
(T in Kelvin)
As T rises, λ drops
Bluer with temperature
300K
5500
106
100,000A
5500
30
Earth
Sun
X-ray source
Stefan-Boltzman Law
L = σAT
4
σ = 5.67x10-5
A is area in cm2
T in Kelvins
Example: The Sun
L = 5.7x10-5 x 4 x 3.14 x (7x1010cm)2 x (5500K)4 = 4 x 1033 ergs
4x1033ergs = 4x1026 Watts = 100 billion billion MegaWatts!!
Emission Lines
Electron Drops
Energy Levels of H
Photon Escapes
Can Only Happen Between
Certain Pre-determined orbitals
Each Element Has Different Orbitals
So Each Element Has Different Lines
Spectrum of Hydrogen
Absorption Lines
Light moving through cold
gas can have photons removed.
Creates dark wavelengths
called absorption lines
Stellar Classification
Full range of surface temperatures from 2000 to 40,000K
Spectral Classification is Based on Surface Temperature
Hottest
O
B
A
F
G K M
{ } Kiss Me
Oh Be A Fine
Girl
Guy
Each Letter has ten subdivisions from 0 to 9
0 is hottest, 9 is coolest
Coolest
Stellar Classification (2)
Sun
α Cen
Sirius
Antares
Rigel
G2
G2 + K5
A1
M1
B8
O5
B5
A5
F5
G5
K5
M5
40,000K
15,500
8500
6580
5520
4130
2800
Letters are odd due to confusion in sorting out temperature scale
between 1900 and 1920
The Doppler Shift
vt
ct
Observer
D
During t seconds, source emits n waves of wavelength λ.
They move ct during that time.
But source also moves vt during that time.
So the n waves are scrunched into ct-vt instead of the usual ct
Thus the wavelength is reduced from λ to
λ
(
ct − vt
c−v
=λ
= λ 1− v
c
ct
c
)
The Doppler Formula
⎛
⎝
v⎞
c⎠
λ = λ0 ⎜1 − ⎟
δλ λ0 − λ V
=
=
λ0
λ0
c
v is positive if coming toward us
Wavelength λ decreases from lab value
δν v − v0 V
=
=
ν0
v0
c
Frequency shifts up as source approaches
The H-R Diagram
Plot of Brightness vs Temperature
-5
Giants
Rigel
Capella
Brightness
0
Sirius
Procyon
Sun
+5
Main Sequence
α Cen B
White Dwarfs
+10
Sirius B
Prox Cen
+15
O
B
A
F
G
Spectral Type
K
M
MS Lifetime
What determines amount of time a star stays on Main Sequence?
Just like a kerosene heater: Amount of fuel and rate of burn.
More Mass = More Fuel
More Luminosity = Greater Burn Rate
We can scale from the Sun: M = 1M~
L = 1L~
Sun lasts 1010 years
M
MSLife = 10
L
10
M in solar masses
L in solar luminosities
Some Lifetimes
Sun
Sirius
Prox Cen
Rigel
Mass
Luminosity
Lifetime in Billion Years
1
2
.4
8
1
10
.001
10,000
10
2
4000
.008
Dinky little stars like Prox Cen will last trillions of years
Huge stars like Rigel are gone in a few million
There aren’t many large stars out there, because they don’t last.
10,000 O stars of the 100,000,000,000 Milky Way stars
Chemical Energy for Sun?
Chemical Energy Generates 2eV per atom in forming molecule (burning)
2eV = 3x10-19 Joules
Number of Atoms in Sun:
M
2 x1030 kg
N=
=
= 1057
− 27
m p 1.6 x10 kg
Available Energy
E = 3 x10 −19 x1057 = 3 x1038 J
Time it can run:
E 3 x1038 J
11
t= =
=
7
x
10
s = 20,000 years
26
L 4 x10 W
Gravitational Energy?
Available Gravity Energy:
Time it can run:
(
GM 2 6 x10−11 x 2 x1030
E=
=
R
7 x108
)
2
24 x1049
41
=
=
3
x
10
J
8
7 x10
E 3 x10 41
15
7
t= =
=
=
10
s
3
x
10
years
26
L 3 x10
Sun can only run 30million years on gravity.
It does this during formation
Best understanding of Sun until Einstein.
Nuclear Energy for Sun?
Nuclear Energy Generates 2MeV per atom in forming molecule (burning)
2MeV = 3x10-13 Joules
Number of Atoms in Sun:
E = 3 x10 −13 x1057 = 3 x10 44 J
Available Energy
Time it can run:
M
2 x1030 kg
N=
=
= 1057
− 27
m p 1.6 x10 kg
E 3 x10 44 J
17
t= =
=
7
x
10
s = 20,000,000,000 years
26
L 4 x10 W
Sun can run 20 Billion years on nuclear energy
Which is what it does.
Outer Envelope of Star Expands
Force of photon flux from below lifts outer parts of star.
Core gets smaller and hotter, but
Surface gets larger and cooler.
What’s Happening in Core?
H
H
H->He
H->He
He
In the center, H is depleted, but He too cool to burn.
“Shell Burning” describes source of nuclear power around dead center
Electron Degeneracy
•Helium Density Rises
•Center of Sun has density of 10g/cc
•When density in center of star reaches ~30,000g/cc
•a new phenomenon kicks in
•Electron Degeneracy
•A purely quantum mechanical phenomenon
Helium Flash
When degenerate He core reaches about 108K, the nuclei
can burn by the Triple Alpha Reaction. (He+He+He->C)
They start to burn and release energy. Pressure rises and temperature
rise, but volume does not increase. P and T rise some more.
Finally, P gets so great it lifts the degeneracy and thermal pressure
equilibrium is re-established.
This is the “He Flash”
Could blow a star apart, but it doesn’t.
After the Flash
H
H
H->He
H->He
He->C
He->C
C
Helium Burns in the Center
Starts to Development Dead C Core
Red Giants
Earth Orbit
Nucleus
Planetary Nebulae
Gas blown out into space and
illuminated by central star.
The star is the degenerate C core.
The Ring Nebula
Hourglass 2
Next Explosion is
Constrained and Expands
as Hour-Glass
White Dwarfs
•
•
•
•
Held up by electron degeneracy
About the size of the Earth R~5000km
Mass Typically 0.8M~
Luminosity ~ .001 L~
Thin layer of “normal” H
Degenerate Carbon
Some Famous White Dwarfs
• Sirius B
• 40 Eridani B
• Procyon B
All in binaries around nearby stars.
Establishes the WD is close and small.
Earth vs White Dwarf
Mass Radius Relation
1
R∝ 3
M
As mass increases star gets smaller.
Like ball of foam.
WD Density
2 x1033
6
ρ=
=
= 1.5 x10 g / cc
8 3
4 3 4 x(7 x10 )
πR
3
M
Water has a density of 1 g/cc
Lead 11 g/cc
Gold 19 g/cc
100,000 times density of gold!
NOT NORMAL MATTER!!
1 cubic centimeter masses one ton!
Surface Gravity
GM 7 x10 −11 x 2 x1030
6
2
a= 2 =
=
3
x
10
m
/
s
R
(7 x10 6 ) 2
This 300,000 gees
If you weigh 150lbs on Earth, you would weigh
45 million pounds on a White Dwarf!
What would happen to you and your spaceship?
Escape Velocity
2GM
2 x6.7 x10 −11 x 2 x1030
13
6
Ve =
=
=
4
x
10
=
6
x
10
m/s
6
R
7 x10
Speed of light is 3x108 m/s, so escape velocity is .02c.
Chandrasekhar Limit
A peculiarity of Degeneracy Pressure is that it has a maximum mass.
Each electron added must find its own quantum state by having its
own velocity.
But what happens when the next electron has to go faster than light?
The Chandrasekhar Limit for a White Dwarf is 1.4M~
No White Dwarf Can have more than 1.4M~
Otherwise it will groan and collapse under its own weight.
We’ll come back to this later.
WDs are Common
Every star with less than 5M~ will end up as a White Dwarf
Most stars with mass above 1.3M~ have reached end of MS life.
White Dwarfs are VERY common ~ 10% of all stars
Closest is only 2.7pc away. (Sirius B)
Will become increasing common as universe ages.
Immortal Stars
Regular stars need thermal pressure to balance gravity, and they
need nuclear reactions to maintain the pressure, so the die when they
run out of fuel.
Not so White Dwarfs. They are as stable as a rock. Literally.
A quadrillion years in the future all the stars will be gone, but the
White Dwarfs will still be here.
Their glow is fossil energy left from their youth as a regular star.
Might die in 1031 years if protons prove to be unstable themselves.
That’s 10,000,000,000,000,000,000,000,000,000,000 years!
Really don’t know if universe will still be here.
Binary Stars
•
•
•
•
•
•
Optical Double
appear close together but aren’t really binary
Visual Binary
orbiting, but we can see them both
Astrometric Binary proper motion wiggles to show orbit
Spectrum Binary
spectra of two stars of different type
Spectroscopic Binary Doppler shift shows orbital motion
Eclipsing Binary
light varies
Half of all stars are in binaries….
Binary stars are formed at birth.
Both components will have same age and composition.
Can vary in mass
Can be very distant (0.1pc) or touching
Spectroscopic Binary
Variable Stars
Some stars just expand and contract.
Eclipsing Binary
Algol – “The Devil Star”
Close Binaries
Equal Energy Curves
Gravity
Mid-Point
Contact Binaries
Very Close
Touching
Common Envelope
Two Nuclear Cores
“W Ursa Majoris” star
Mass Transfer Binary
Accretion Disk
Material Swirls In
Friction allows the material to fall
and heats while it falls.
All the way to the surface
Energy Released
GMm 6.7 x10 −11 x 2 x1030 x1
E=
=
= 2 x1013W / kg
6
R
6 x10
Huge amounts of energy are released as the material swirls in.
Material get hot. Really hot. Like a million degrees Kelvin.
Emits ultraviolet and x-rays.
We can see these accretion disks with x-ray telescopes!
A Newtonian Black Hole
Energy Falling To Surface
Kinetic Energy
GMm 1 2
= mv
2
R
OR
2GM
R= 2
c
if v=c
Schwarzschild Radius
2GM
R= 2
c
Two errors cancel.
This is the radius of the “Event Horizon”
The event horizon is a true singularity in space-time.
It is a place where time and space cease to exist.
Properties - Size
2GM
R= 2
c
R=
2 x6.7 x10 −11 x 2 x1030
(3x10 )
8 2
= 3000m
The radius of a black hole is 3km per solar mass
There is no limit on size or mass.
Note: Volume rises as the cube of the mass. Implies the larger the black
hole gets, the lower is its density.
A sphere of water the size of Saturn’s orbit would be a black hole!
Properties – Escape Velocity
No way.
Not even light can escape.
No signal can escape
No particle
Nothing
Properties – Orbital Period
2πRS 6.28 x3000
P=
=
= 60 μs
8
c
3 x10
Material orbiting a black hole will have milli-second periods
Properties - Basic
1. Mass (Schwarzschild Black Hole)
2. Electric Charge (doesn’t happen)
3. Angular Momentum (Kerr Black Hole)
4. Thermal Temperature
No “Surface” Features
No Magnetic Fields
No Pulsing
“No Hair”
Properties – Energy Emitted
• Energy Released
from accretion
• about 0.1mc2
Time Dilation
δt =
δt∞
RS
1−
r
Some event takes δt∞ out in free space.
Same event takes place at radius r from center of a black hole.
Now view it from free space.
Takes δt instead. Longer. It looks like things are moving slower.
If you are near the black hole, the rest of the universe appears to be moving faster.
Time Dilation
δt =
δt∞
RS
1−
r
As r approaches Rs δt gets longer and longer.
When r reaches the event horizon, time stops.
We know how to make a time machine with a forward switch only!
Just fly to a black hole and orbit above the surface.
But you can fall in really fast as viewed from outside.
Hawking Radiation
The vacuum makes pairs of
electrons and positrons that pop
into existence and then annihilate
without any net effect.
Above a black hole, one can get
sucked in. The other annihilates
above the surface to cause
radiation.
Since its close to the surface, the
light gets redshifted escaping,
but it carries energy with it!
100 Billion Stars
Orbital Period
R3
(10000 x3 x1016 ) 3
15
8
= 6.28 x
=
3
x
10
s
=
10
years
P = 2π
−11
12
30
GM
6.7 x10 x10 x 2 x10
Takes the Sun 200million years to orbit Milky Way.
Sun is 4600 million years old.
The Sun is 23 Galactic Years Old.
Milky Way – Edge-On
Formation of Milky Way
• Analogous to formation of the Sun
• Start with big blob of gas
• Let it collapse
Disk Stability Again
Globular Clusters
Gas has friction and collapses to disk.
Stars have huge momentum with small cross section.
When a star forms it remains frozen in its initial orbit forever.
Little knots of high density
are first to form into stars.
These are the globular clusters.
They each contain a million stars.
There are about 100 orbiting the
Milky Way.
Black Hole in Milky Way
Dead Center in the
middle of the Milky Way.
2.7 Million Solar Masses!
Rotation Curves
Winding Problem
In under a billion years spirals
would be wiped out.
Spiral Density Waves
Interstellar Medium
• 10% of normal matter in gas – 90% stars
• New stars form from this gas
• Fundamental Part of the evolution of
galaxy
• Very Dynamic Place
Reflection Nebulae
HII Regions
Star Forming Regions
High Density leads to
high star formation
Dust Cloud
• Dust forms from C,O,Si,Fe etc.
• Like dust storm at sunset
• Reddens stars beyond
Molecular Clouds
Dust in Space
Dark dust clouds
Very cold in the middle & shielded from UV
Molecules Form
H, C, N, O
H2
H2O
NH3
CH4
Even Ethyl Alcohol!
Bubbles
Stellar Wind
Interstellar Gas
Supernova Remnants
• Four Phases
•
•
•
•
Free Expansion 200 years
Energy Conserving
10,000years
Momentum Conserving 100,000 years
Confusion 1,000,000years
Super Bubbles
Shock Wave
Hot Bubble
New Stars Form
Superbubble Grows
Takes Millions of Years to Grow
Galactic Fountain
Hot Material Churns Upwards
Rains back down
Galactic Halo
Galactic Fountain
Much like a bubble bath
Local Group
MW
M31
Magellanic Clouds
M33
M31
The Great Nebula in Andromeda
M33
The Third Wheel of the Local Group
Our Region
15,000,000pc
Local Group
Virgo Cluster
M81,82
Hubble Sequence
(not an evolutionary sequence!)
Rotation Curves
Without Dark Matter
Hydrogen emits a radio emission line at λ = 21cm
Doppler shift allows us to measure orbital velocity of gas clouds vs radius
Dark Matter
Mass to Light Ratio:
Mass in Solar Masses divided by Luminosity in Solar Luminosities
Sun has M/L of 1 (by definition)
Rigel M=20 L=2000 --Æ M/L = .01
Pros Cen M=.1 L = .001 Æ M/L = 100
Galaxies typically have M/L of 7 to 10
Something like 85% of the mass is dark matter
Dark Matter
Dark matter is in Ball Æ We can measure its distribution even though
we don’t know what it is.
Dark Matter
Regular Matter
What is Dark Matter?
WHAT IS DARK MATTER?????
Some possibilities:
Ionized Gas
Small Stars
Planets
Baseballs
Black Holes
Neutrinos
Neutralinos
A flaw in Newton’s Laws
MAssive Compact Halo Objects (Machos)
Weakly Interacting Massive Particles (Wimps)
Astronomers don’t know what most of the matter in the universe is!
Cluster of Galaxies
CD Galaxy
A Galactic Cannibal
M87 has eaten 100 of its own.
The Distance Scale
All the things astronomers have done to gain a handle on distance
Parallax
to 100pc
I year cycle
Main Sequence Fitting
to 55,000pc
Plot enough stars and the
Main Sequence becomes
clear.
This works out to Magellanic
Clouds.
Beyond that, MS stars too
faint
Period-Luminosity Relationship
Cepheids are bright and can be seen at very large distances.
Type I Supernovae
All Type Ia supernovae are the same brightness. That white dwarf that implodes
and then explodes is always about the same. And they’re bright. You can see them
at billions of parsecs!
Apparent magnitude can be converted to distance.
Redshift of Galaxies
Hubble found that
galaxies are redshifted.
The absorption lines are
those of the stars that
make up the galaxy.
Hubble’s Law
The more distant the galaxy,
the greater the redshift.
The more distant is the galaxy,
the faster it is flying away from
us.
v = H 0d
H0=70 km/s/Mps
A Modern Hubble Diagram
Expanding Universe
Current Universe
Early Universe
The volume of the universe is
increasing.
The Age of the Universe
v = Hd
⎛1⎞
d = ⎜ ⎟v
⎝H⎠
d = vt
Notice: At time zero, d = 0
All galaxies are at zero distance!
The universe has zero volume!
when t=1/H
The Begining
1
t=
H0
H = 70km / s / Mpc = 70 x1000m / s /(3 x1016 x10 6 m) = 2.3 x10 −18 s −1
1
17
H=
=
4
x
10
s = 13Billion _ years
−18
2.3 x10
Before 13 billion years ago, there was no before.
Time and space started with the Big Bang
We will return to this in a few more lectures
The Cosmic Web
The Redshift
λ − λ0
z=
λ0
z = 0 implies local
z of 1 or more implies near far edge of universe
Seyfert Galaxies
Quasar
QUAsi Stellar Radio source Æ Quasar
(Sometimes QSO)
Completely enigmatic for 1960-1980
Jets
Cygnus A
Full Model
Superluminal Expansion
Radio interferometers
see blobs emitted by
AGN’s from base of jet.
Watch them expand.
Know distance, so can
measure speed.
v = 900,000km/s
v = 3c
Superluminal ! ?
Is Einstein’s ghost worried?
The Intergalactic Medium
The Cosmic Web
Structure of the Universe
Where is the center of the Universe?
Where are the edges?
What happens if you fly to the edge and stick your finger through?
Newtonian Universe must be infinite.
Cosmological Principle: The Universe is Everywhere the Same
(when averaged over grand scale)
Cosmological Principle
• Cosmological Principle applied to
expanding Euclidean Universe
• New matter must be formed of nothing to
keep density everywhere the same.
Olber’s Paradox
If universe is infinite with stars everywhere,
then there an infinite number of stars.
Any line of sight will eventually intersect the
surface of star. Sky would be as bright as the
surface of the Sun.
Well it isn’t. So why not?
Geometry of Universe
Space Curves
in on itself
There’s no path
out!
Negatively Curved Universe
Its warped so it cannot close back on itself.
Is infinite in extent.
Open vs Closed
Universe is either open or closed.
If closed:
Positive Curvature
Finite Mass
Finite Lifetime
Finite Volume
If open:
Negative Curvature
Infinite Mass
Infinite Volume
Infinite Lifetime That’s
INFINITY Folks!!!
Astronomers have prejudice in favor of closed universes.
All measurements have been inconclusive. We live near the edge!
Critical Density
• Whether Universe is open or closed
depends on the average DENSITY of
matter.
• Above 10-29 g/cc the universe is closed
• Below 10-29 g/cc the universe is open
• We are very close to that density
• Coincidence?
ρcrit is about 1 atom per liter
History and Fate of Universe
Universe is one of these (maybe).
Best Guess Size
• Diameter of Universe is about 1024 times
larger than the part we can see.
• That makes the volume 1072 times larger.
• But still finite
• How big is 1072 ?
Heat Death of Universe
•
•
•
•
If universe is open, then it will last forever
But stars will all burn out 1014 years
Protons decay 1031 years
Orbits will decay into black holes at center
of the galaxies 1060 years
• Giant black holes evaporate 10100 years
• Nothing left but redshifting photons
More on Infinite Universe
• If Cosmological Principle
holds and universe is
infinite, there’s infinite
mass.
• Infinite Planets
• Infinite Earth-like planets
• Infinite planets just like
you.
• Infinite You’s
• Far away: About
10118
10
meters away
The Origin of it All?
• Good Question
• Perhaps a bubble in a hyper-universe
• Perhaps its “unknowable”
• But it appears Universe started as a very
tiny bubble. How small, we don’t know.
The “Planck Era”
• When quantum fluctuations exceed the radius of
the universe our theories are definitely
inadequate.
• R < 10-35m
• t < 10-44 seconds
• Density of Universe > 1093 g/cc
• T > 1032 K
• Then it starts to expand and cool….
The Inflationary Universe
• Idea: Vacuum of space-time created with
excess energy Æ folded upon itself
• At t=10-37s, T=1028K, starts to relax
• From 10-37 to 10-33s it expands by the
creation of new space.
• Universe expands from 10-28m to 0.1m
• That’s 10cm in 10-33s = 1032m/s
v = 3x1023 c !!!
The Annihilation Era
• After inflation settles down and resumes normal
expansion
• So hot that matter and anti-matter are in
equilibrium.
• For every 100,000,000 antimatter particles,
there are 100,000,001 matter particles.
• Basic Asymmetry From Planck era is not
understood, but it’s why we’re made of matter.
.001 Seconds
• Jump from 10-33s to 10-3s
• T = 1012K
• Neutrons and Protons now have cooled so
that can annihilate with anti-neutrons and
anti-protons.
• Leave mostly photons and an occasional
particle of matter.
1 Second
• Electrons and Positrons have cooled to
point where they are no longer in
equilibrium. T=1010K
• Create photons.
• One matter particle in hundred million is
left.
• Those are today’s electrons.
Era of Nucleosynthesis
• T = 109 K
• t = 100s
• Hydrogen and Helium form from neutrons
and protons.
• Tiny amounts of Li and Be are created.
• No carbon: density too low for triple alpha
• This is when the initial elements form
The Plasma Era
• From 100s to 100,000 years universe is a
soup of ionized hydrogen and helium
• But its expanding and cooling
• Ends at 100,000years when the
temperature falls below 3000K.
• Hydrogen and Helium nuclei combine with
electrons to form neutral atoms
• At that moment, universe becomes
transparent
Sky Aglow
• At moment of de-ionization, sky is glowing as
blackbody at 3000K (M star)
• Photons released are no longer re-absorbed
• They travel into the universe and are travelling
today
• But they redshift.
• Now 1000 times longer wavelength than then
(makes them microwaves)
The Cosmic Microwave
Background
• Microwave Antenna at Bell Labs – 1965
• Penzias and Wilson
• Microwaves coming from sky, but not Earth.
Uniformly
• Predicted as part of a “Big Bang” by Gamov in
the early 1950’s
• Inescapable proof of the “Big Bang”
• Killed all steady state theories
• Now we’re studying it.
At 100 Million Years
• No Galaxies yet – or perhaps
protogalaxies
• Gas mostly smooth through universe
• Clumps cause gravitational spots that
create even greater density fluctuations.
• Size:
• Remember: Dark matter dominates
Primordial Density Enhancements
Grow
• Now (12.4Billion
years) we have
structure
• Galaxies and clusters
Dark Energy
• Expansion of
Universe is
Accelerating!!!
• Implies New
Inflationary Era
(Why Now?)
• Acceleration takes
energy
New Cosmology
•
•
•
•
70% of mass is Dark Energy (E=mc2)
25% of mass is Dark Matter
3.5% of mass is in Intergalactic Medium
1.5% of mass is regular matter in galaxies
• Together they add to exactly critical density.
• We’re right on the edge of open/closed
• Universe is either finite and very big, or infinite.