Solar Interior/ Nuclear Fusion

Charles HakesFort Lewis College 1


Solar Interior/

Nuclear Fusion


Outline

• Solar interior• Fusion• Solar evolution• Stars


Review

• Sunspots…• are darker because they are actually

cooler than the rest of the Sun• the result of a “kink” in the magnetic field• size of Earth; usually come in pairs• magnetic field switches every 11 year;

cycle is 22 years • Maunder minimum corresponded to mini

ice age


Review

• and…• The solar equator rotates faster than the poles • the Zeeman effect is a splitting of spectral lines

from magnetic fields• sunspots magnetic field is about 1000x greater

than the surrounding area• solar wind is the sun evaporating


As the Sun rotates, an individual sunspot can be tracked across its face.

From Eastern to Western limb, this takes about:A) 12 hours

B) A week

C) Two weeks

D) A month

E) 5.5 years


As the Sun rotates, an individual sunspot can be tracked across its face.

From Eastern to Western limb, this takes about:A) 12 hours

B) A week

C) Two weeks

D) A month

E) 5.5 years


Compared to the Earth, the Sun’s average density is:

A) lower

B) about the same

C) much greater


Compared to the Earth, the Sun’s average density is:

A) lower

B) about the same

C) much greater


From inside out, which is the correct order?

A) core, convective zone, radiative zone

B) photosphere, radiative zone, corona

C) radiative zone, convective zone, chromosphere

D) core, chromosphere, photosphere

E) convective zone, radiative zone, granulation


What about the internal structure?


Solar Composition

Element

Number Percent

Mass Percent

H 91.2 71

He 8.7 27.1

O 0.078 0.97

C 0.043 0.4

N 0.0088 0.096


Figure 9.2Solar Structure


What about the internal structure?

• Core - • temperatures hot enough for nuclear reactions

• Radiation Zone - • Temperatures cooler, so no nuclear reactions.• Hot enough so everything is ionized. • Atoms can’t absorb photons.

• Convection Zone - • Temperature cooler. • Atoms form and can absorb radiation.


Figure 9.6Solar Interior


How do we know what is inside the Sun?


How do we know what is inside the Sun?

Standard model


Figure 9.4Stellar Balance


Figure 9.5Solar Oscillations


Figure 9.7Solar Convection


Figure 9.8Solar Granulation


Figure 9.11Solar Spicules

• dynamic jets• 5-10 minute life• possibly related

to seismic activity


Typically, a granule in the photosphere of the sun is about the size of?

A) A city, ~20-30 kilometers across.

B) Texas, ~1000 km across.

C) The Earth, ~12,000 km across.

D) Jupiter, ~100,000 km across.


Typically, a granule in the photosphere of the sun is about the size of?

A) A city, ~20-30 kilometers across.

B) Texas, ~1000 km across.

C) The Earth, ~12,000 km across.

D) Jupiter, ~100,000 km across.
















Misc notes

• Problem 9.1 - note that Mercury’s orbit is very eccentric, so you can’t simply use the semi-major axis for it’s distance at perihelion.



Nuclear Fusion


Forces in Nature

• Gravity - long range; relatively weak.• Electromagnetic - long range; responsible

for atomic interactions (chemistry)• Weak Nuclear Force - short range;

responsible for some radioactive decay• Strong Force - short range; holds nuclei

together


Nuclear Fusion

• Combining light nuclei into heavy ones.

nucleus 1 + nucleus 2 = nucleus 3 + energy

• Law of conservation of mass and energy

E = mc2


Figure 9.25Proton Interactions

• Like charges (two protons) repel by electromagnetic force.

• With enough energy (temperature) and pressure, can overcome EM force


Proton-Proton chain

• Most common reaction in the Sun.4 protons >->->-> helium-4 + 2 neutrinos + energy

• Many other reactions are possible, but 90% are the proton-proton chain.

• Calculate energy produced from mass differences. (use E=mc2), get 4.3x10-12 J (Joules) when 4 protons fuse to Helium.

• From Sun’s luminosity, can calculate that 600 million tons of Hydrogen per second are fused into Helium.


Figure 9.26Solar Fusion


Proton-Proton chain

• Neutrinos - “little neutral one” are almost mass-less, and react with almost nothing.


Figure 9.27Neutrino Telescope - Super Kamiokande

• Need large amounts of matter to detect neutrinos

• Solar Neutrino Problem - until recently could not explain observed low numbers.


Proton-Proton chain

• Neutrinos “oscillations” explain the observation discrepancy.

• Neutrinos take eight minutes to get to the Earth from the Sun.

• In that time they can mutate (oscillate) into other forms.


Three Minute Paper

• Write 1-3 sentences.• What was the most important thing

you learned today?• What questions do you still have

about today’s topics?

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Solar Interior/ Nuclear Fusion

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