Solar Interior

1 The P-P Chain in the SUN

+ Step 1: p + p ⇒ D + e + ν e e+ + e- ⇒ 2γ (1.02 MeV) Step 2: D + p ⇒ 3He + γ (5.49 MeV) Step 3: 3He + 3He ⇒ 4He + 2p (12.86 MeV)

Need two of Step 1 & 2 to have one of Step 3 - 4 Net: 4p + 2e ⇒ He + 6γ + 2ν e (~ 26 MeV) (Where 1 MeV = 106 eV = 1.6 x 10-13 J) (2*1.02MeV) + (2*5.49MeV) + (1*12.86MeV) = 25.88 MeV 2

The Solar Interior:

The result of the models is a complex structure that can be broken down into distinct regions.

3 The Solar Core:

• Extends out to 0.2 Rsun

• Contains ~50% of the Sun’s Mass.

• Contains ~2% of the Sun’s Volume.

• Is bounded (loosely) by the point where temperature and density are too low to support P-P fusion.

4 The Radiative Zone:

• Extends from 0.2-0.7 Rsun

• Contains ~48% of the Sun’s Mass.

• Contains ~32% of the Sun’s Volume.

• Contains free electrons and atomic nuclei (plasma)

• The radiative zone is bounded by the point where temperature and density are low enough to permit atoms to hold some of their electrons.

5 Solar Energy Transport: Core and Radiative Zone Radiative Diffusion (Random Walk):

• Occurs in the Core and Radiative Zones.

• Light scatters randomly off free electrons and nuclei and looses energy in the process (Gamma -> UV/Visible). • This is a SLOW process. • A photon produced by Fusion in the core today will take 105 – 106 YEARS to exit the radiative zone!

6 The Convective Zone:

• Extends from 0.7-1.0 Rsun

• Contains ~2% of the Sun’s Mass.

• Contains ~66% of the Sun’s Volume.

• Some of the electrons in this region are bound to nuclei.

• The convective zone is bounded by the point where Light Directly Escapes From the Solar Atmosphere (The Visible `Surface` or Photosphere).

7 The Standard Model for the Sun

Lead

Water

Deepest Ocean Trench 8 Energy/Mass Transport in the Convective Zone:

Energy in the convection zone is transported with matter.

Rising Rising • Hot Gasses Rise from Deep in the Zone, Expanding and Cooling as they do.

• At the top of the Zone the gas Becomes Cooler than its Surroundings and Sinks Back Falling Falling Falling Down. • These Rising and Falling Regions form Adjacent Convective Cells.

9 Doppler Effect

Sound Waves

Red shiing of absorpon lines

Light Waves 10 Time and Size Scales in the Convective Zone:

• These Cells Vent Solar Energy like Water Boils. Each one Lasts for ~10 Minutes.

• Cell Structure Exists on Many Scales in the Sun, with Detectable Regions up to 105 km Across.

11 Time and Size Scales in the Convective Zone:

Granules are convecon cells about the size of Texas (121,000 km2; 350kmx350km); image shows 1% of sun surface. Each delivers equivalent to 1000 yrs of Hoover Dam energy in 5 minutes

12 Time and Size Scales in the Convective Zone:

Granules are convecon cells about the size of Texas (121,000 km2); image shows 1% of sun surface. Each delivers equivalent to 1000 yrs of Hoover Dam energy in 5 minutes

13 Caught in a Box:

Sound waves reflect from the top of the Sun’s atmosphere without penetrating.

• The photosphere is very diffuse and sound doesn’t travel well.

• The change in density and the inability of the wave to penetrate further leads to an internal reflection. • The wave goes back in the direction that it came from, but the interaction moves the photosphere up and down.

upwelling down welling

Incoming wave Outgoing wave14 Resonances:

• Some waves traverse the Sun and come back on themselves. Others will resonate (or come into phase) with each other.

• The penetration depth of the sound waves depends on their original direction and the way the Sun’s characteristics change with depth.

15 Helioseismology:

The study of solar sound wave oscillations is called helioseismology.

• We use the same technique on the Earth!

• Earthquakes make the entire planet ring.

• By looking at where, when, and what type of earthquake waves reach different parts of the planet, we can determine the structure of the Earth’s interior!

• At the Sun we can do the same thing. We can also use them to probe the back side of the Sun. 16 What does Helioseismology tell us?:

Each ’Harmonic’ of the Sun carries specific information about the interior.

• How does pressure, density, temperature, and composition change with radius in the sun?

• Predict what is coming

hp://gong.nso.edu/data/farside/ 17 The Michelson Doppler Imager (MDI):

• MDI takes Dopplergrams of the solar ‘surface’ to study both the interior structure and the rotation rate of the Sun.

• MDI has identified many rotational characteristics of the Sun including changes with latitude and depth. It’s a complex fluid that plays a big role in the topic of sunspots and the solar cycle! 18 The Solar Atmosphere:

The base of the solar atmosphere is called the ‘Photosphere’ because this is where nearly all the light energy comes from.

• Photosphere: The photosphere is really just the visible ‘surface’ of the sun. It is the thin (~300 km thick) altitude range where convective cells break and the Sun’s blackbody radiation is emitted. • It’s 6000K, and produces the bulk of the light from the Sun.

Sharp edge is an illusion. Negative hydrogen ions (H with an extra electron) here absorb all light from below and re-emit it.

19 The Chromosphere:

• Chromosphere: The chromosphere is a diffuse region from 300 to 10,000 km above the photosphere.

• Most of the chromosphere is hotter than the photosphere and reaches up to 20,000K.

20 The Chromosphere:

• Chromosphere: The chromosphere is a diffuse region from 300 to 10,000 km above the photosphere.

• The chromosphere is hotter than the photosphere and reaches up to 20,000K.

• The Chromosphere is easily observed by looking at the Hα transition of Hydrogen.

• In Chromosphere images we see many structures, including filaments, arching prominences, and sunspots (these are active).

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Prominences & Filaments

Filament

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