week8 astro1 sun
TRANSCRIPT
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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
How does the Sun Shine?
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Until mid-19th Century:
Time to burnout: ~10,000 years
Assumed made of iron basedupon ̀ meteorite evidence ’
How does the Sun Shine?
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
How does the Sun Shine?
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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!):
How does the Sun Shine?
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Full details of howthis happens called`Standard SolarModel’
How does the Sun Shine?Nuclear Fusion
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How does the Sun Shine?Nuclear Fusion
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
How does the Sun Shine?Nuclear Fusion
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
How does the Sun Shine?Nuclear Fusion
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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How does the Sun Shine?Nuclear Fusion
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…
# Weakly Interacting Signal
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
# Weakly Interacting Signal
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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DetectorThe image cannot be displayed. Your computer may not have enough memory to open the image, or the image may have been corrupted. Restart yourcomputer, and then open the file again. If the red x still appears, you may have to delete the image and then insert it again.
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