ASTR 1020 General Astronomy: Stars and...
Transcript of ASTR 1020 General Astronomy: Stars and...
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
221
12 rmGmF =
221
21 rmGmF =
(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.
221
reeFe =Electrical Force Equation Similar
ExampleCalculate the period of a planet that is the same distance from the starSirius that the Earth is from the Sun.
r=1.5x1013cmG=6.7x10-8
M=4x1033g
sxxxxxx
xxxx
xP 76121326
39
338
313
105.2102510153.6105.13.6105.2
1043.6104107.6)105.1(28.6 ====== −
About 9 Months
Escape Velocity
RGMmmv =2
21Fall from Large Height
Same Energy Needed to Reverse and Fly Away
RGMve
2=
R
Escape velocity is the speedat which object must be thrownupward to escape and never comedown.
Surface Gravity
2RGMmF =
2RGMmma =
Force of Gravity at Surface of Body is
So
or 2RGMa =
The acceleration of a bodynear the surface.Independent of mass.
Remember Galileo and the Leaning Tower of Pisa
Formation of the Solar SystemUniverse is about 12 Billion Years old (3x1017s)Milky Way 10 Billion Years oldSun 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 ByThermal Pressure From Below
Individual Atoms Don’tOrbit Entire Inside ofStar Like This
They Jostle Each OtherBut Effect Is The Same
Outer MassGravity
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
Cosmic Composition
• H hydrogen 89% by number• He helium 11%• O oxygen 0.1%• C carbon 0.06%• N nitrogen 0.015%
Pretty much the composition of the entire universe.Sun and Jupiter have this compositionEarth does not.
Proton-Proton Chain
Bottom Line: H+H+H+H → He
1H1 +1H1 → 1H2 + e+ + ν
1H2 +1H1 → 2He3 + γ
2He3 +2He3 → 2He4 + 1H1 + 1H1
5x106 < T < 2x107K
CNO Cycle
6C12 +1H1 → 7N13 + γ
7N13 → 6C13 + e+ + ν
6C13 +1H1 → 7N14 + γ
7N14 +1H1 → 8O15 + γ
8O15 → 7N15 + e+ + ν
7N15 +1H1 → 6C12 + 2He4
Net: 1H1 +1H1 + 1H1 +1H1 → 2He4 + 2e+ + 4γ +2ν
hydrogen -> helium + energy
2x107 < T < 108K
Triple-α Reaction
2He4 +2He4 ⇔ 4Be8 + γ
4Be8 +2He4 → 6C12 + γT < 108K
Net: 2He4 +2He4 + 2He4 +2He4 → 6C12 + 2γ
helium -> carbon + energy
Must be very dense for this to workBe8 decays back into helium very quicklyunless struck by another He4
Too low densityin Big Bang
Star Names
• Arabic Names– Antares, Capella, Mira, etc.
• Constellationsα Orionis, β Cygni, … then 49 Ori, 50 Ori, etc.
• Catalogues HD80591, SAO 733421, etc• RA and Dec – just position in the sky
Proper Motion
All stars move
Nearby stars move faster
Appear to move against fixed field
Can Take Many YearsUse Old Photographic Plates
1900
2003
The Parsec
1AU
1 parsec
1 arcsecond
360 degrees in circle60 arcminutes per degree60 arcseconds per arcminute
200,000AU = 1 parsec = 3x1018cm
parsec ---- parallax second
The Magnitude SystemPtolemy 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 howthe naked eye responds. Also, faintest were about 100x fainter thanbrightest.
Break the factor of 100 into 5 equal factors: 51.21001 5 ==mag
Start with Vega m=1Polaris 2.51x fainter m=22.5x fainter than Polaris m=32.5x fainter than that m=4etc
Absolute Magnitude
5log5 10 +−= dmM
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?
The magnitude a star would have were it at 10pc
At 10 times closer the star would be 100x brighter = 5 magnitudes
M = 10-5 = 5
5510105100log510 =+−=+−=M
Light Waves
λlambda is lower case Greek Lstands 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 MagneticFields Sloshing BackAnd Forth
Parts of EM Spectrum
Radio λ > 1mm (107A)Infrared 1mm> λ > 10000ΑVisible 10,000Α > λ > 3500ΑUltraviolet 3500Α > λ > 100ΑX-ray 100A > λ > 0.1AGamma-ray 0.1A > λ
Speed of Light
Speed of Light c = 3x1010cm/sThat’s a very odd statement
1 car at 130mph
2 cars at 65mph
Cover same distance in same amount of timeThe Relative speeds are the same
Frequency
λλ λ λ
Moves λ during each cycle
Frequency is the number of cycles per second, ν Greek “nu”
Moves distance λ for each of ν cycles each second
c=λν
Energy of a Photon
νε h=
h = 6.63x10-27 erg s Planck’s Constant
ergsxxxx 121427 104106106.6 −− ==ε energy of yellow photon
Sunlight is 107 ergs/cm2/s Outside we have 1019 photons/cm2/s hit us
Spectroscopy
Spectrum is plot of number of photons as a function of wavelengthTells us huge amounts about nature of object emitting light.
Thermal Radiation
1
125
2
−=
kThc
e
hcIλλ
Planck’s Law
Temperature Determines Where Spectrum Peaks
Position of Peak Determines Color
Wien’s Law
Tx
peak
7103=λ
As T rises, λ dropsBluer with temperature
Å (T in Kelvin)
300K 100,000A Earth5500 5500 Sun106 30 X-ray source
Stefan-Boltzman Law
4ATL σ= 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 LinesElectron Drops
Photon Escapes
Can Only Happen BetweenCertain Pre-determined orbitals
Each Element Has Different OrbitalsSo Each Element Has Different Lines
Spectrum of Hydrogen
Energy Levels of H
Absorption Lines
Light moving through coldgas can have photons removed.
Creates dark wavelengthscalled absorption lines
Stellar Classification
Full range of surface temperatures from 2000 to 40,000K
Spectral Classification is Based on Surface Temperature
O B A F G K M
Oh Be A Fine GirlGuy
Kiss Me
Each Letter has ten subdivisions from 0 to 90 is hottest, 9 is coolest
CoolestHottest
{ }
Stellar Classification (2)
Sun G2α Cen G2 + K5Sirius A1Antares M1Rigel B8
O5 40,000KB5 15,500A5 8500F5 6580G5 5520K5 4130M5 2800
Letters are odd due to confusion in sorting out temperature scalebetween 1900 and 1920
The Doppler Shiftvt
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 ( )cv
cvc
ctvtct
−=−
=− 1λλλ
ct
The Doppler Formula
⎟⎠⎞
⎜⎝⎛ −=
cv10λλ
cV
=−
=0
0
0 λλλ
λδλ v is positive if coming toward us
Wavelength λ decreases from lab value
cV
vvv
=−
=0
0
0νδν
Frequency shifts up as source approaches
The H-R DiagramPlot of Brightness vs Temperature
O
Spectral Type
+10
+5
-5
Brig
htne
ss
0
+15B MA F G K
Sun
Sirius
α Cen B
Prox Cen
Procyon
RigelCapella
Sirius B
Main Sequence
Giants
White Dwarfs
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 FuelMore Luminosity = Greater Burn Rate
We can scale from the Sun: M = 1M L = 1L
Sun lasts 1010 years
LMMSLife 1010= M in solar masses
L in solar luminosities
Some Lifetimes
Mass Luminosity Lifetime in Billion Years
Sun 1 1 10Sirius 2 10 2Prox Cen .4 .001 4000Rigel 8 10,000 .008
Dinky little stars like Prox Cen will last trillions of yearsHuge 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 Generates 2eV per atom in forming molecule (burning)2eV = 3x10-19 Joules
Number of Atoms in Sun:
Chemical Energy for Sun?
5727
30
10106.1102
=== − kgxkgx
mMN
p
JxxxE 385719 10310103 == −
yearssxWxJx
LEt 000,20107
104103 11
26
38
====
Available Energy
Time it can run:
Gravitational Energy?
( ) Jxxx
xxxx
RGME 41
8
49
8
230112
1031071024
107102106
====−
Available Gravity Energy:
Time it can run: yearsxsxx
LEt 715
26
41
10310103103
====
Sun can only run 30million years on gravity.It does this during formation
Best understanding of Sun until Einstein.
Nuclear Energy Generates 2MeV per atom in forming molecule (burning)2MeV = 3x10-13 Joules
Number of Atoms in Sun:
Nuclear Energy for Sun?
5727
30
10106.1102
=== − kgxkgx
mMN
p
JxxxE 445713 10310103 == −
yearssxWxJx
LEt 000,000,000,20107
104103 17
26
44
====
Available Energy
Time it can run:
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, butSurface gets larger and cooler.
What’s Happening in Core?
H->He
H H
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 nucleican burn by the Triple Alpha Reaction. (He+He+He->C)
They start to burn and release energy. Pressure rises and temperaturerise, but volume does not increase. P and T rise some more.
Finally, P gets so great it lifts the degeneracy and thermal pressureequilibrium is re-established.
This is the “He Flash”
Could blow a star apart, but it doesn’t.
After the Flash
H H
Helium Burns in the Center
H->He
He->C
H->HeHe->C
C
Starts to Development Dead C Core
Planetary Nebulae
The Ring Nebula
Gas blown out into space andilluminated by central star.
The star is the degenerate C core.
White Dwarfs
• Held up by electron degeneracy• About the size of the Earth R~5000km• Mass Typically 0.8M• Luminosity ~ .001 L
Degenerate Carbon
Thin layer of “normal” H
Some Famous White Dwarfs
• Sirius B• 40 Eridani B• Procyon B
All in binaries around nearby stars.Establishes the WD is close and small.
WD Density
ccgxxx
x
R
M /105.1)107(4
102
34
638
33
3===
πρ
Water has a density of 1 g/ccLead 11 g/ccGold 19 g/cc
100,000 times density of gold!
NOT NORMAL MATTER!!
1 cubic centimeter masses one ton!
Surface Gravity
2626
3011
2 /103)107(102107 smx
xxxx
RGMa ===
−
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
smxxx
xxxxR
GMVe /106104107
102107.622 6136
3011
====−
Speed of light is 3x108 m/s, so escape velocity is .02c.
Chandrasekhar LimitA peculiarity of Degeneracy Pressure is that it has a maximum mass.
Each electron added must find its own quantum state by having itsown 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 theyneed nuclear reactions to maintain the pressure, so the die when theyrun 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 theWhite 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 massCan be very distant (0.1pc) or touching
Mass Transfer Binary
Accretion Disk
Material Swirls InFriction allows the material to falland heats while it falls.
All the way to the surface
Energy ReleasedkgWx
xxxxx
RGMmE /102
1061102107.6 13
6
3011
===−
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!
Schwarzschild Radius
2
2cGMR = 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
2
2cGMR =
( ) mx
xxxxR 3000103
102107.6228
3011
==−
The radius of a black hole is 3km per solar massThere is no limit on size or mass.
Note: Volume rises as the cube of the mass. Implies the larger the blackhole 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
sxx
cRP S μπ 60
103300028.62
8 ===
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” FeaturesNo Magnetic FieldsNo Pulsing
“No Hair”
Time Dilation
rR
ttS−
= ∞
1
δδ
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
rR
ttS−
= ∞
1
δδAs 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 ofelectrons and positrons that popinto existence and then annihilatewithout any net effect.
Above a black hole, one can getsucked in. The other annihilatesabove the surface to causeradiation.
Since its close to the surface, thelight gets redshifted escaping,but it carries energy with it!
Orbital Period
yearssxxxxx
xxxGMRP 815
301211
3163
1010310210107.6)10310000(28.62 ==== −π
Takes the Sun 200million years to orbit Milky Way.
Sun is 4600 million years old.
The Sun is 23 Galactic Years Old.
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 densityare first to form into stars.
These are the globular clusters.
They each contain a million stars.There are about 100 orbiting theMilky Way.
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
Molecular CloudsDust in Space
Dark dust clouds
Very cold in the middle & shielded from UV
Molecules Form
H, C, N, O
H2H2ONH3CH4
Even Ethyl Alcohol!
Supernova Remnants
• Four Phases
• Free Expansion 200 years• Energy Conserving 10,000years• Momentum Conserving 100,000 years• Confusion 1,000,000years
Galactic Fountain
Hot Material Churns UpwardsRains back down
Galactic Fountain
Much like a bubble bath
Galactic Halo
Rotation Curves
Hydrogen emits a radio emission line at λ = 21cmDoppler shift allows us to measure orbital velocity of gas clouds vs radius
Without Dark Matter
Dark MatterMass 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 -- M/L = .01
Pros Cen M=.1 L = .001 M/L = 100
Galaxies typically have M/L of 7 to 10Something like 85% of the mass is dark matter
Dark MatterDark matter is in Ball 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 GasSmall StarsPlanetsBaseballsBlack HolesNeutrinosNeutralinosA 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!
Main Sequence Fittingto 55,000pc
Plot enough stars and theMain Sequence becomesclear.
This works out to MagellanicClouds.
Beyond that, MS stars toofaint
Type I Supernovae
All Type Ia supernovae are the same brightness. That white dwarf that implodesand then explodes is always about the same. And they’re bright. You can see themat billions of parsecs!
Apparent magnitude can be converted to distance.
Redshift of Galaxies
Hubble found thatgalaxies are redshifted.
The absorption lines arethose of the stars thatmake 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 fromus.
dHv 0=H0=70 km/s/Mps
The Age of the Universe
Hdv =
vH
d ⎟⎠⎞
⎜⎝⎛=
1 vtd =Notice: At time zero, d = 0
All galaxies are at zero distance!
The universe has zero volume!
when t=1/H
The Begining
0
1H
t =
118616 103.2)10103/(/100070//70 −−=== sxmxxsmxMpcskmH
yearsBillionsxx
H _13104103.21 17
18 === −
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
Superluminal ExpansionRadio interferometerssee blobs emitted byAGN’s from base of jet.
Watch them expand.
Know distance, so canmeasure speed.
v = 900,000km/s
v = 3c
Superluminal ! ?
Is Einstein’s ghost worried?
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 thesurface of star. Sky would be as bright as thesurface of the Sun.
Well it isn’t. So why not?
Open vs ClosedUniverse is either open or closed.
If closed: Positive CurvatureFinite MassFinite LifetimeFinite Volume
If open: Negative CurvatureInfinite MassInfinite VolumeInfinite 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
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 1181010 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 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.