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 Net: 4p + 2e- ⇒ 4He + 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
Falling
Rising
Falling
•  Hot Gasses Rise from Deep in
the Zone, Expanding and
Cooling as they do.
Falling
•  At the top of the Zone the gas
Becomes Cooler than its
Surroundings and Sinks Back
Down.
•  These Rising and Falling Regions form Adjacent Convective
Cells.
9 Doppler Effect Sound Waves Red shiLing of absorpOon 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 convecOon 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 convecOon 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
14 Outgoing wave
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
h_p://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
18 plays a big role in the topic of sunspots and the solar cycle!
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).
21 Prominences & Filaments Filament 23