Week8 Astro1 Sun

8/17/2019 Week8 Astro1 Sun

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Our Friend, the Sun

Mass 2x1030 kg

Radius 7x105 km

Central temperature 15 million K

Surface temperature 5780 K

Composition 75% hydrogen

(by mass) 25% helium


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Our Enemy, the Sun

Mass 2x1030 kg

Radius 7x105 km

Central temperature 15 million K

Surface temperature 5780 K

Composition 75% hydrogen

(by mass) 25% helium


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How does the Sun Shine?

Two Stories


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Antiquity: Greeks/Egyptians/Aztecs…

Time to burnout: Infinite



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Until mid-19th Century:

Time to burnout: ~10,000 years

Assumed made of iron basedupon ̀ meteorite evidence ’


The sun puts out 4x1026 Joules/second

Heating oil yields

46.2x106

J/kg;Mass of the Sun isabout 1030kg so if itwere made entirely ofoil that is 4.62x1037 Jpossible over its

lifetime---4.62x1037/4x1026 s isabout 1011s=10,000 yrs.


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Mid-19th Century:

Time to burnout: ~30 million years

Gravitational energy converted into thermal energy

Not happy



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1919

A star is drawing on some vast reservoir of energy by means

unknown to us. This reservoir can scarcely be other than the

sub-atomic energy which, it is known, exists abundantly in allmatter… The store is well-nigh inexhaustible, if only it could be

tapped. There is sufficient [energy] in the Sun to maintain its

output of heat for 15 billion years….

If, indeed, the sub-atomic energy in the stars is being freely used

to maintain their great furnaces, it seems to bring a little nearer to

fulfillment our dream of controlling this latent power for the well-

being of the human race--or for its suicide.

Sir Arthur Eddington suggests solar fusion (and nuclear weapons!):



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Full details of howthis happens called`Standard SolarModel’

How does the Sun Shine?Nuclear Fusion


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By squeezing protons (hydrogen atoms) together the Sunconverts hydrogen to helium. But a helium atom weighs lessthan 4 times 1 hydrogen atom. What happens to the massthat has been lost?


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!

Mass of Hydrogen Atom – 1.008 AMU! Mass of a Helium Atom – 4.00260 AMU

! 4 hydrogen -> one helium - 4.032 AMU!

Mass of a Helium Atom – 4.002 AMU

! Difference is 0.03 AMU

! 1 atomic mass unit = 1.66 ! 10-27 kg


E=mc2 Some of the mass is converted to energy!

So E=mc2 = 0.03 AMU x 1.66x10-27 kg/AMU x (3x108 m/s)2 = 4.5x10-12 Joules for every 4 hydrogen atoms

Doesn’t sound like much…but how many H atoms in 1 kg?

About 6x1026! Or 6x1015 J/kg! (Compare to oil!)


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Lsun = 4 x 1026 Joules/second

E = mc2 = 4 x 1026 Joules (energy produced each second)

===" m = 4.4 x 109 kg of matter is converted to energyEACH SECOND!

BUT: For every kilogram of Hydrogen I burn, only 7 gramsgets converted to energy (our 6x1015 J/kg)

=" So, this means that we burn ~6 x 1011 kg of Hydrogen asecond

or 2 x 1019 kg/year "

The Sun can burn 10% of its Hydrogen or 2 x 1029kg" So the Sun will burn for 1010 years


So how long can the Sun burn?

(m=E/c2)


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A direct measurement of the rate of nuclear fusion reactions in

the Sun finds that in fact the Sun is making helium at a rate of

1x1038 atoms/second. If this is true, what should the luminosity

of the Sun be?!" #"$%&'() +,-./010

2" &"3 % &'&& +,-./010

4" $"(%&'() +,-./010

5" 67 08,-.9:;7 / ?/A B0


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A direct measurement of the rate of nuclear fusion reactions in

the Sun finds that in fact the Sun is making helium at a rate of

1x1038 atoms/second. If this is true, what should the luminosity

of the Sun be?

E=mc2

C=3x108 m/s4MH-MHe =0.03 AMU1 AMU = 1.66 ! 10-27 kg

!" #"$%&'() +,-./010

2" &"3 % &'&& +,-./010

4" $"(%&'() +,-./010

5" 67 08,-.9:;7 / ?/A B0


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This is a nice theory.

Does it make any falsifiable predictions?

That we can test today, rather than weighting 1010 years?

There is one prediction, but this is part of another story…


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Invention of the Neutrino

The perplexing mystery of beta decay:Should give electron of sameenergy every time

But observed spectrum is continuous

Mass of neutron > (mass of proton+electron) and E=mc2

Not on exam


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Wolfgang Pauli suggests a third particle (1930)

Designed to be impossible to detect…almost.

Invention of the NeutrinoNot on exam


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e -

!

# Weakly Interacting Signal

Detecting Neutrinos

A block of matter

Not on exam


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!

Add more matter…


Detecting Neutrinos

A block of matter

Not on exam


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!

!

!

!

!

!

!

!

!

!

!

!

!

Or use more neutrinos…eV keV MeV GeV TeV

CNB Radioactive nuclei Reactors

The Sun

Supernovae

Atmospherics

Accelerators

Cosmic sources


Detecting Neutrinos

A block of matter

Not on exam


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µ µ µ µ µ µ µ µ µ µ

# Backgrounds: Muons from Space

Detecting Neutrinos Not on exam


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# Backgrounds: Natural Radioactivity

Detecting Neutrinos Not on exam


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Reines and Cowan’s original idea

Los Alamos Science, 25 , (1997)

Discovery of the Neutrino Not on exam


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`Standard Model’ Neutrinos

• Come in three `flavors’ (!e, !µ, ! #)• Are massless

•

Interact weakly • Cannot change flavor

Our best theory of the microscopic Universe…

Neutrinos:

Over twenty years of tests confirmed

even The most subtle predictions.

Not on exam


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Neutrinos and the Sun

If neutrinos can travelthrough anything, theneven those produced inthe core can travel to us!

(How long does it take?)

(John Bahcall)


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Experiments need to be:

• Big to detect weakly interacting n’s•

Deep to get away from cosmic rays

• Clean to reduce radioactivitiy

Solar Neutrino ExperimentsNot on exam


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Solar Neutrino Experiments

First experiment by Davis et al in 1960’sRadiochemical Method (Chlorine):

Found ~ 1/3 of expected rate!


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•

Are experiments wrong?• Or solar theory?• Or the neutrino?

What’s Going On??

Solar Neutrino ExperimentsAfter six solar neutrino experiments and 35 years…

“Solar Neutrino Problem”


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Neutrinos Changing Flavor?How can neutrinos change from one type to another?

Particles have wavelike properties.

If a !e is the sum of two wavesand a nm is the sum of those twowaves shifted relative to oneanother

then a !e can change into a !µ if Wave 1 (!1) travels at adifferent speed than Wave 2 (!2)

This can happen if the neutrinos have different masses.

Not on exam


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Herb Chen’s Idea (1984):Use Heavy Water

ES

CCNC

Not on exam


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Where to put it?

Sudbury, Ontario(Canada)


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Creighton Mine


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Sudbury Highlights Not on exam


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Sudbury Neutrino Observatory (SNO)

1700 tons Inner

Shielding H2O

1000 tonnes D2O

5300 tons Outer

Shield H2O

12 m Diameter

Acrylic Vessel

Support

Structure for

9500 PMTs

Urylon Liner and

Radon Seal


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Underground…


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…but in the Lab.

Not on exam


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From your textbook


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ConstructionNot on exam


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SNO Solar NeutrinosNot on exam


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Why This is HardOnly 3000 of these dots are neutrinoevents…the rest is radioactivity

Not on exam


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Results

Herb Chen’s original idea becomes possible:

(sensitive to all flavors equally) (sensitive only to !e)

NC CC

Main Question: Is number of ! ’s measured with NC > CC??

Not on exam


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Results


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PublicityNot on exam


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PublicityNot on exam


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EpilogueWon Nobel 2002 Nobel Prize!Did not win2002 Nobel Prize


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What Do I Need to Know?

• How energy is generated in the Sun•

That neutrinos tell us about those reactions• How to calculate the energy generated, and the Sun’s

lifetime• That Ray Davis did the first solar neutrino experiment

•

That the Sudbury Neutrino Observatory (SNO) solvedthe “solar neutrino problem.”

But not:

•

Details about the 3 generations of matter• Matter vs. antimatter• Details about neutrino “oscillations”• The details of how SNO worked


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!

Mass of Hydrogen Atom – 1.008 AMU (“Atomic Mass Units”)! Mass of a Helium Atom – 4.00260 AMU

! 4 hydrogen = 4.032 AMU! Mass of a Helium Atom = 4.002 AMU! Mass of 2 positrons (2Me+) = 2/1837 AMU!

Mass of 2 neutrinos= at least a million times smaller than e+!

! Difference is 0.03 AMU

! 1 atomic mass unit = 1.66 ! 10-27 kg

Summary of Energy GenerationE=mc2 Some of the mass is converted to energy!

Doesn’t sound like much…but how many H atoms in 1 kg?

About 6x1026! Or 6x1015 J/kg! (Compare to oil!)

Nuclear Fusion: MHe+2Me++2M!< 4Mp


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Summary of Energy Generation• How long can the Sun burn?

Lsun = 4 x 1026 Joules/second

E = mc2 = 4 x 1026 Joules (energy produced each second)

===" m = 4.4 x 109

kg of matter is converted to energyEACH SECOND!BUT: For every kilogram of Hydrogen I burn, only 7 grams

gets converted to energy (our 6x1015 J/kg)

=" So, this means that we burn ~6 x 1011 kg of Hydrogen asecond

or 2 x 1019 kg/year "

The Sun can burn 10% of its Hydrogen or 2 x 1029kg" So the Sun will burn for 1010 years


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The Sun

In the Sun, an exactbalance between theinward pull of gravity andthe outward pressure ofenergy release ismaintained.

Also, the Sun radiatesfrom its surface exactlyas much energy as itproduces in its core.


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The photosphere is the layer visible toour eyes. It’s temperature is ~5800 K.Sometimes spots are visible. At higherresolutions, granulation is seen.

The larger granules are roughlythe sizes of continents on Earth.They are rising bubbles of gas onthe Sun, changing appearanceconstantly.

The SunPhotosphere and Granules


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The hot gas rises. When it gets near the surface it radiates and cools.It then flows back down.

The SunGranules and Convection


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Above the photosphere, the density drops off dramatically into the

reddish chromosphere and whitish corona, but the temperature jumpsto almost 106 K! BUT, while it is VERY hot, it has very low density.

The SunChromosphere and Corona


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Spicules rise abovethe chromosphere.

From Kirkoff’sLaw’s what kind ofspectrum is this?

Chromosphere‘Chromosphere’ because of color


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ChromosphereAnatomy of a Spicule


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Which of the following is not a region of the

Sun?

!" D8,7,0E8/@/

2" 48@,F,0E8/@/

4"

4,@,:=5" 4-/@C,


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The Sun Must Support Itself


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Overall, the Sun is notnoticeably expanding orshrinking. It is inequilibrium. Thisprecise balance ofinward and outwardpressure is calledhydrostatic equilibrium.Simply knowing that

this exists allowed usto begin constructingtheoretical models ofthe interior of the Sun.

Hydrostatic EquilibirumBalancing pressure and gravity


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Pressure waves on the surface of the Sun

Helioseismology`Earthquakes’ on the Sun

Watching the way the seismic waves ripple tells us about the

solar interior


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10,000 km acrossUmbra – 4500 KelvinPenumbra - 5500 Kelvin

Sun Spots


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The number of sunspots risesand falls with an 11-yearperiod. This is called the

sunspot cycle. The Sunswitches polarity of itsmagnetic field every twocycles, or 22 years. We don’tknow why.

This cycle may be connectedwith weather here on Earth, inways we do not reallyunderstand.

The Sun Changes


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Sunspot Cycles

`


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Sunspots `migrate’ in Bands

d h


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Sunspots and Weather?

l M i Fi ld


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The magnetic field “pops out” of the surface forming a loop.

Solar Magnetic Field

Magnetic field lines get `wound up’

S l M i Fi ld


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The Magnetic Field at aSunspot is 1000 timesgreater than the rest ofthe Sun.

Sunspots are coolerthan the photospherebecause the high

magnetic field“redirects” theconvection from thelower layers….

Solar Magnetic FieldSunspots occur near high magnetic fields

S l M ti Fi ld


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Solar Magnetic FieldQuiet versus active Sun(Using ultraviolet lens)

S l P i


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The magnetic field loopsthat create sunspots canfunnel gas through spaceto create arch-shapedprominences. These

bubbles of gas can lastfrom hours to days.

Solar ProminencesFollow Magnetic Field Loops

Can release about

1/10 of the energythe Sun puts outeach second

S l P i


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Solar Prominences

S l Fl


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-

Release as much energy asa Prominence – but inminutes, not days!- Temperatures up to

100,000,000K !!!- Can eject BILLIONS oftons of matter into thesolar system

Solar Flares

Big ones disruptcommunications on Earth

S l Fl


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Solar flares can send enormous plumes of gas intospace; these are called coronal mass ejections. Ifthe Earth is in the path of a CME, we can getaurorae.

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Solar FlaresCoronal Mass Ejections

C l M Ej ti


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Watch the stars in the background. What’s happening?

Coronal Mass EjectionsProton `showers’


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Sunspots appear to be caused by:

!" G,.=@ H=@/0

2" G,.=@ E@,FB:/:


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Summary• What are the important regions of the Sun?

• Core: T = 15 million K, where fusion takes place converting

hydrogen (H) to helium (He)• Radiative zone: Just outside the core, energy is transferred byradiation (photons) traveling through the material

• Convective zone: Next outward, energy is transferred towardsurface by movement of material (like boiling)

• Photosphere: Top of the convective zone, it is what we see as

the Sun’s “surface.” It has “granules” and sometimes sunspots.T= 5700 K.

• Chromosphere: Just above the photosphere, it is a hot, thin gas,with an emission line spectrum and “spicules” that poke up intothe next layer, and sometimes “prominences” and “solar flares”that release huge amount of material into space.

•

Corona: Very hot (> 1 million K) and very thin layer of gas,extending more than a solar radius out from the chromosphere.

L st Tim


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Last Time

• What are sunspots?•

Small, dark regions on the photosphere•

They are cooler than the surroundingphotosphere by a few hundred degrees K.

• They have high magnetic fields.•

Magnetic fields are “wound up” as the Sunrotates.

•

Sunspots come in cycles: 11 years betweenmaximum activity

•

Solar magnetic field switches polarity every22 years.

The Sun at Different Wavelengths


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The Sun at Different Wavelengths

Week8 Astro1 Sun

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