test 2 results
Post on 20-Jan-2016
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Slide 1
test 2 distribution
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1 2 3 4 5 6 7 8 9 10 11
score bins
nu
mb
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f st
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ents
Test 2 results
Test 2 average: 77 (test 1: 82)Test 2 median: 79 (test 1: 87)
Slide 2
SOHO: The Solar and Heliospheric Observatory
1.5 million km from the Earth at the L1 point
Slide 3
The Lagrange Points
L4,5: Trojans (stable points)L1: SOHOL2: WMAPL3: empty
(unstable points)
Slide 4
Gravitational potential in the corotating frame
Slide 5
What we want to know:
• Internal structure and composition
• Source of energy
• Lifetime
Slide 6
Slide 7
Life of stars:Gravity is everything
• Stars are born due to gravitational collapse of gas clouds
• Star’s life is a battle between thermal pressure generated by nuclear reactions and gravity
• Eventually, a star loses this battle, and gravity overwhelms
Slide 8
Gravity is balanced by thermal gas pressure
Stars are held together by gravity. Gravity tries to compress everything to the center. What holds an ordinary star up and prevents total collapse is thermal and radiation pressure. The thermal and radiation pressure tries to expand the star layers outward to infinity.
Slide 9
Stars are gravitating spheres: they are held together by their own gravity. The gravity force acting on each volume element of a star is exactly balanced by gas pressure (Hydrostatic equilibrium)
This balance is steady
gravity
gas pressure
No gravity: the Sun will disperse in 1 day
No gas pressure: the Sun willcollapse in 20 minutes
km/s103
m
Tkv Bthermal
22
2
m/s274;2
~ R
GMg
gtR Central pressure ~ 1010 atmospheres
Slide 10
Hydrostatic equilibrium
Temperature in the center of a star
A =1 m2
RRAM column
R
GM
R
GMMP
~
2gravitycolumn
TkP thermal=
K10~ 7
kR
GMTc
Slide 11
Internal structure
Central temperature Tc 1.5107 K
Surface temperature Tc 5800 K
Heat transfer from the center to the surface!
Heat transfer determines both the internal compositionand the luminosity of the Sun
Slide 12
Internal source of energy
• Gravitational energy?
• Chemical energy?
• Nuclear reactions?
The Sun’s luminosity is L = 4x1026 Watt. Where does this energy come from?
Slide 13
Chemical energy?
This is the energy associated with breaking chemical bonds in molecules
1. Typical energy released per proton is ~ 1-10 eV
2. There are M/mp ~ 1057 protons in the Sun
Total available energy is Echem ~ 10x1057 = 1058 eV ~ 2x1039 J
Chemical energy will be radiated away during the time
years105chem L
Et
But the Sun’s age is at least 4.6 billion years!Also, there is too hot for molecules in the sun
Slide 14
Note:
If E is total energy stored in the sun (in J);
L is luminosity, or the rate with which this energy is spent(in J/sec);
Then the time it takes to spend all energy is T = E/L sec
Slide 15
Gravitational energy?
J104 41R
GMMU g
As the Sun radiates its thermal energy to outer space, it shrinks, and the central temperature is increased (!)
The energy source is the gravitational energy of a star
If the energy is radiated away with luminosity L = 4x1026 J/s,The Sun would radiate all its energy during the time
years103 7L
Ut g
But the Sun’s age is at least 4.6 billion years!
Slide 16
Nuclear reactions?
Slide 17
Nuclear reactions?
• Fission: decay of heavy nuclei into lighter fragments
•Fusion: synthesis of light nuclei into a heavier nucleus
Energy released per proton is ~10-20 MeV!!
Slide 18
Energy is released in fusion reaction if the sum of masses of initial nuclei is larger that the mass of the final nucleus
mp + mp
MD + me < 2 mpDeuterium
Positron (antielectron)
neutrino
Deuterium has larger binding energy than protons (more tightly bound)
M = 2 mp- MD - me
Energy released E = M c2
Famous Einstein’s relation: E = mc2
hydrogen
hydrogen
Slide 19
What is binding energy?
It exists due to attractive forces between parts of a compound system: protons and neutrons in a nucleus, electrons and ion in an atom, Earth and moon, etc.
Binding energy is negative!: Ub = -|Ub|
Total energy of a system is the sum of energies of its parts plus binding energy:
E = E1 + E2 + Ub = E1 + E2 - |Ub|
Slide 20
Energy is released in fission reaction if the mass of an initial nucleus is larger that the sum of masses of all final fragments
MU > MRb + MCs + 3 mn
Rubidium and Cesium are more tightly bound, or have larger binding energy than Uranium.
It is energetically favorable for Uranium to split.
When is the energy released in fission reactions?
M = MU – (MRb + MCs + 3 mn)
Energy released E = M c2
Famous Einstein’s relation: E = mc2
Slide 21
There are no heavy elements on the stars
|Ub|
Slide 22
Energy ProductionEnergy generation in the sun
(and all other stars):
Nuclear Fusion
= fusing together 2 or more lighter nuclei to produce heavier ones.
Nuclear fusion can produce energy up to the production of iron;
For elements heavier than iron, energy is gained by nuclear fission.
Binding energy due to strong force = on short range, strongest of the 4 known forces: electromagnetic, weak, strong, gravitational
Slide 23
Slide 24
Proton-proton cycle: four hydrogen nuclei fuse to form one helium nucleus
Hydrogen Fusion
Slide 25
Einstein’s relation: E = mc2
!04 mmm Hep
J103.4MeV8.26 122 cmE
Energy released in one reaction:
(Binding energy)
kg10048.0 27m
Hans Bethe 1939
0.007, or 0.7% of the rest energy of protons (4mpc2) is released
This is 107 times more efficient than chemical reactions!
Slide 26
There is more than enough nuclear fuel for 1010 years!
years10310104 10
5612
Lt
Does nuclear fusion provide enough energy to power the Sun?
Assume 1056 protons in the core:
Slide 27
600 million tons of hydrogen are fused every second on the Sun!
How much hydrogen should be fused per second to provide the Sun’s luminosity?
W104sec1
007.0 262 cm
L
Nuclear fusion efficiency:0.7% of the hydrogen mass is converted into radiation in the p-p cycle
Matter-antimatter annihilation has even higher efficiency: 100% !!
kg106007.0
104 112
26
c
m
Slide 28
Proton-proton cycle
Slide 29
Proton-proton cycle
Step 1
Step 2
Step 3
All positrons annihilate with electrons creating gamma-quanta
Slide 30
Step 11H + 1H --> 2H + positron + neutrino
To fuse, two protons need to be as close as 10-15 m to each other
They need to overcome the Coulomb barrier
r
keU c
2
Coulomb repulsion energy:
Slide 31
Protons should be hot!
Slide 32
But we need T > 109 K to overcome the Coulomb barrier!
• Quantum tunneling helps
Still, a proton has 1 chance in 10 billion years to fuse!
Such reaction is nearly impossible
Slide 33
Step 2
Takes 6 seconds to occur
Slide 34
Step 3
Takes 1 million years to occur
Slide 35
The solar neutrino problem
Slide 36
•Matter is effected by forces or interactions (the terms are interchangeable) •there are four fundamental forces in the Universe:
•gravitation (between particles with mass) •electromagnetic (between particles with charge/magnetism) •strong nuclear force (between quarks) •weak nuclear force (that changes quark types)
Matter is effected by forces or interactions (the terms are interchangeable)
There are four fundamental forces in the Universe: gravitation (between particles with mass) electromagnetic (between particles with charge) strong nuclear force (between quarks) weak nuclear force (that changes quark types)
Slide 37
10,000 years
Neutrino have zero or very small mass and almost do not interact with matter
Slide 38
Neutrino image of the Sun
Slide 39
The Davis experiment
400,000 liters of perchlorethyleneburied 1 mile deep in a gold mine
About 1 Chlorine atom per day is converted into Argon as a result ofinteraction with solar neutrino
Much more difficult than finding a needle in a haystack!!
There are 1032 Cl atoms in a tank!
Slide 40
Sudbury neutrino observatory: 1000 tons of heavy water D2O
Slide 41
32,000 ton of ultra-pure water13,000 detectors
Slide 42
Slide 43
Slide 44
Observed neutrino flux is 2 times lower than the theoretical prediction!
Slide 45
Slide 46
The problem has been finally solved just recently:
Neutrinos “oscillate”! They are converted into other flavors: mu and tau neutrinos
Neutrinos should have massParticle physics models should be modified
Slide 47
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