ASTR 1020General 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

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

The Nuclear Core

core15x106K

Envelope1 Million K

Photosphere 5000K At Surface

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

Solar Schematic

Sunspot Cycle

During mid 1600’s sunspots became non-existentMaunder Minimum

Photosphere 5500K

Chromosphere 104KTransition Region 105K

Corona 2x106K

Solar Wind 5x105K

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

Parallax

I year cycle

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

Red Giants

Nucleus

Earth Orbit

Planetary Nebulae

The Ring Nebula

Gas blown out into space andilluminated by central star.

The star is the degenerate C core.

Hourglass 2

Next Explosion isConstrained and Expandsas Hour-Glass

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.

Earth vs White Dwarf

Mass Radius Relation

3

1M

R ∝

As mass increases star gets smaller.Like ball of foam.

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

Spectroscopic Binary

Variable Stars

Some stars just expand and contract.

Eclipsing Binary

Algol – “The Devil Star”

Close Binaries

GravityMid-PointEqual Energy Curves

Contact Binaries

Very Close

Touching

Common EnvelopeTwo Nuclear Cores “W Ursa Majoris” star

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!

A Newtonian Black Hole

2

21 mv

RGMm

=

Energy Falling To Surface Kinetic Energy

2

2cGMR =

OR

if v=c

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”

Properties – Energy Emitted• Energy Released

from accretion

• about 0.1mc2

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!

100 Billion Stars

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.

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 densityare first to form into stars.

These are the globular clusters.

They each contain a million stars.There are about 100 orbiting theMilky Way.

Black Hole in Milky Way

Dead Center in themiddle of the Milky Way.

2.7 Million Solar Masses!

Rotation Curves

Winding Problem

In under a billion years spiralswould 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 tohigh star formation

Dust Cloud

• Dust forms from C,O,Si,Fe etc.• Like dust storm at sunset• Reddens stars beyond

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!

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 BubblesShock Wave

Hot Bubble

Superbubble Grows

Takes Millions of Years to Grow

New Stars Form

Galactic Fountain

Hot Material Churns UpwardsRains back down

Galactic Fountain

Much like a bubble bath

Galactic Halo

Local Group

MW

Magellanic Clouds

M31

M33

M31 The Great Nebula in Andromeda

M33The Third Wheel of the Local Group

Our Region

Local Group

M81,82

Virgo Cluster

15,000,000pc

Hubble Sequence

(not an evolutionary sequence!)

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!

Cluster of Galaxies

CD Galaxy

A Galactic CannibalM87 has eaten 100 of its own.

The Distance Scale

All the things astronomers have done to gain a handle on distance

Parallaxto 100pc

I year cycle

Main Sequence Fittingto 55,000pc

Plot enough stars and theMain Sequence becomesclear.

This works out to MagellanicClouds.

Beyond that, MS stars toofaint

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 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

A Modern Hubble Diagram

Expanding Universe

Early Universe

Current Universe

The volume of the universe isincreasing.

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

The Cosmic Web

The Redshift

0

0

λλλ −

=z

z = 0 implies local

z of 1 or more implies near far edge of universe

Seyfert Galaxies

Quasar

QUAsi Stellar Radio source Quasar

(Sometimes QSO)

Completely enigmatic for 1960-1980

Jets

Cygnus A

Full Model

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?

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 thesurface of star. Sky would be as bright as thesurface of the Sun.

Well it isn’t. So why not?

Geometry of Universe

Space Curvesin on itself

There’s no pathout!

Negatively Curved Universe

Its warped so it cannot close back on itself.

Is infinite in extent.

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

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 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.