Transcript Sun Physics

Sun Physics
Basic Fusion Reactions in the Sun
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Assembled by
Ken Mitchell
Livermore TOPScience
From Core to Corona
Layers of the Sun
Core Temperature and Pressure are key to
fusing Hydrogen into Helium
When temperatures exceed 10 Million Degrees Kelvin the kinetic
energy is large enough overcome the coulomb barrier to start the
proton-proton reaction.
p + p  d + b+ + n + 0.42 MeV
When enough deuterium (d) is present, the proton-deuteron
(deuterium) reaction begins.
p + d  He3 + g + 5.5 MeV
See the cartoon on the next slide
b+ (Positron)
Two
Hydrogen
Nuclei
(Protons)
+0.42 MeV
Deuteron
n (Neutrino)
The p – p Reaction
One
Deuteron
Plus One
Hydrogen
Nuclei
Gamma Ray
+ 5.5 MeV
Helium 3
Nuclei
The p – d Reaction
This next leads to:
He3 + He3  He4 + 2p + 12.8 MeV
The overall result of the above series of reactions is
4p  He4 + 2b+ + 2g + 2n + 26.7 MeV
Where: p = proton, b+ = positron,
g = gamma, and n = neutrino
See the cartoon on the next slide.
Helium 3
Nuclei
Alpha
Particle
Proton
12.8 MeV
Helium 3
Nuclei
Helium 4
Nuclei
Proton
The He3 – He3 Reaction into He4
The energy is in particle velocity.
Copy the URL into your browser:
http://www.astro.ubc.ca/~scharein/a311/Sim/fusion/Fusion.html
for an active p -- p fusion animation. Click on instructions.
The Reaction Summary
The reaction process depicted above is the dominant fusion
mechanism in light stars, including our sun.
In the P-P chain, two pairs of protons fuse, forming two
deuterons.
Each deuteron fuses with an additional proton to form
helium-3.
The two helium-3 nuclei which then fuse to create beryllium6, which is unstable (5.9 x10-21 seconds) and disintegrates
into two protons plus a helium-4 (alpha particle).
In addition, the process releases two neutrinos, two
positrons, and gamma rays. The positrons annihilate quickly
with electrons in the plasma, releasing additional energy in
the form of gamma rays.
The neutrinos interact so weakly that they fly right out of the
sun immediately.
"P-P": Solar Fusion Chain
Summary Diagram
Hot Stuff
Sun’s core is about 27 million degrees F and is about ten
times the density of Lead.
Each second it fuses 600 Megatons of Hydrogen into
595 Megatons of Helium.
The mass difference is 5 Million tons of energy, which is
the equivalent of about 1 Billion 1 MT H-Bombs..
Solar Envelope
Outside of the core is the radiative envelope, which is
surrounded by the convective envelope. Radiative Zone is
about 185,000 miles thick. Convection Zone is about
130,000 miles thick. Protons do a “Random Walk” delaying
their exit for thousands to millions of years.
The temperature is 4 million degrees Kelvin (7 million
degrees F).
The density of the solar envelope is much less than that of
the core. The core contains 40 percent of the sun's mass in
10 percent of the volume, while the solar envelope has 60
percent of the mass in 90 percent of the volume.
The solar envelope puts pressure on the core and maintains
the core's temperature.
Convection Zone
"Convective cells are arranged in tiers
containing cells of progressively smaller size
as the surface is neared.
Photosphere
The photosphere is the zone from which the sunlight we see is
emitted.
The photosphere is a comparatively thin layer of low pressure
gasses surrounding the envelope.
It is only a few hundred kilometers thick, with a temperature of
6000 K.
The composition, temperature, and pressure of the
photosphere are revealed by the spectrum of sunlight. In fact,
helium was discovered in 1896 by William Ramsey, when in
analyzing the solar spectrum he found features that did not
belong to any gas known on earth.
The newly-discovered gas was named helium in honor of
Helios, the mythological Greek god of the sun.
From Core to Corona
Layers of the Sun
Chromosphere
In an eclipse, a red circle around the outside of the sun can
sometimes can be seen.
This is the chromosphere. Its red coloring is caused by the
abundance of hydrogen.
From the center of the sun to the chromosphere, the
temperature decreases proportionally as the distance from
the core increases.
The chromosphere's temperature, however, is 7000 K, hotter
than that of the photosphere.
Temperatures continue to increase through the corona.
Annular Solar Eclipse over Spain
Sunspots
Sunspots are dark spots on the photosphere, typically with the
same diameter as the Earth.
They have cooler temperatures than the photosphere. The center
of a spot, the umbra, looks dark gray if heavily filtered and is only
4500 K (as compared to the photosphere at 6000K). Around it is
the penumbra, which looks lighter gray (if filtered).
Sunspots come in cycles, increasing sharply (in numbers) and
then decreasing sharply. The period of this solar cycle is about 11
years. (See PPT on ‘The Sun’ for more details.)
The sun has enormous organized magnetic fields that reach from
pole to pole. Loops of the magnetic field oppose convection in the
convective envelope and stop the flow of energy to the surface.
This results in cool spots at the surface which produce less light
than the warmer areas. These cool, dark spots are the sunspots.
This picture of the sun was taken with heavily
filtered visible light.
Corona
The outermost layer of the sun is the corona. Only visible
during eclipses, it is a low density cloud of plasma with
higher transparency than the inner layers.
The corona is hotter than some of the inner layers. Its
average temperature is 1 million K (2 million degrees F) but
in some places it can reach 3 million K (5 million degrees F).
Temperatures steadily decrease as we move farther away
from the core, but after the photosphere they begin to rise
again. There are several theories that explain this, but none
have been proven.
This picture, showing more turbulence, was taken with x rays.
The heat and energy of the corona cause the emission of x rays
Solar Flares
In the corona, above sunspots and areas of complex
magnetic field patterns, are solar flares.
These sparks of energy sometimes reach the size of the
Earth and can last for up to several hours.
Their temperature has been recorded at 11 million K (20
million degrees F).
The extreme heat produces x rays that create light when
they hit the gasses of the corona.
Small prominences extend from the
chromosphere up into the lower corona.
Prominences
Prominences are generally less violent than solar flares.
They are "cool sheets” of gas that condense out of the
corona above the active regions.
Some are quiet and hang there for weeks, others rain
matter down on the photosphere, still others literally
explode into space, pushing the corona out in front of
them in a great burst that carries the gas off the sun
altogether."
A Solar Prominence (from SOHO)
Coronal Mass Ejections
Large flares are often associated with huge ejections of mass
from the Sun.
Solar plasma is heated to tens of millions of degrees, and
electrons, protons, and heavy nuclei are accelerated to near the
speed of light. The super-heated electrons from CMEs move
along the magnetic field lines faster than the solar wind can flow.
Each CME releases up to 100 billion kg (220 billion lb) of this
material, and the speed of the ejection can reach 1000 km/second
(2 million mph) in some flares.
Solar flares and CMEs are currently the biggest "explosions" in
our solar system, roughly approaching the power in ONE BILLION
hydrogen bombs! (See ‘The Sun’s Magnetic Personality’)
CMEs from SOHO
CMEs with UV Filter over the Sun
Solar Wind
The solar corona is constantly losing particles.
Protons and electrons evaporate off the sun, and reach the
earth at velocities of 500 km/s.
Most of the mass of the sun is held in by magnetic fields in
the corona, but particles slip through occasional holes in the
fields.
Solar wind affects the magnetic fields of all the planets in the
solar system.
When the solar wind hits the Earth's magnetic field, the wind
compresses the field and creates a shock wave called the
Bow shock.
Solar Wind
Solar Wind - - continued
Closer to the Earth are the Van Allen radiation belts where
solar particles are trapped due to magnetic forces.
Still closer are huge rings of electric current around the poles,
formed by the influence of the solar wind on the magnetic
field. Earth, Jupiter, Saturn, Uranus, and Neptune have
magnetotails where the wind extends their magnetic field.
The heliopause is the boundary where the sun's solar wind
hits the gasses of interstellar space.
The sun's particles flow at least to Neptune, and probably
farther. That means that we're inside the sun!