Transcript The Sun, Stars, and Beyond

The Sun
Our Nearest Stellar Neighbor
• Officially known as Sol, as in Solar
System.
• Each star in the sky would be referred to as
a sun by (hypothetical) inhabitants of the
planets that orbit it.
• Like almost all stars, 74% H and 24% He,
with trace amounts of other elements (2%).
Vital Statistics
• 93 million miles away,
• 864,000 miles in diameter (about 100
Earths across, and it would hold
1,000,000),
• 4.567 billion years old, using
Uranium/Saramium radiometric dating.
• Good for another 5 billion.
fire
Fire FIRE!
• Not!
• There is no fire on the Sun;
• A fire of normal combustion with the Sun’s mass
would only last a few thousand years.
• The source of the Sun’s energy is nuclear
fusion—similar to the fusion discussed earlier.
• The Lawson Criteria hold.
Structure
• Largely due to the fusion
process and the energies
it produces.
• The core is where the
fusion occurs,
• The radiative zone
transmits heat to the,
• Convective zone which
moves the heat to the
Photosphere, the surface
of the Sun we see.
Hydrostatic equilibrium
• The balance between
the explosive force of
the fusion at the
center and the
crushing gravity of its
2E30kg
• When it fails the Sun
will change
drastically
Heat Flow
• The core of the Sun is about 15 million degrees.
• Using E = mc2, it converts around 6.5 million
tons of H into energy every second!
• This is 400 million million million million Watts
of power, +/- 0.07%.
• Visible light output varies to a small degree, but
the UV output varies greatly.
• Sunspots a measure of that variability.
Outward
• Above the core, the pressure/temperatures
aren’t sufficient for fusion, so heat is
radiated through a layer of hot gas.
• Eventually, the pressures are low enough
for “normal” convective fluid flow, which
brings the heat to the surface, or
photosphere.
At the Surface
• Many surface features due to the upwelling of
heat.
• Particularly Sunspots and Prominences, as can be
seen with a simple telescope and filter.
• Sunspots are magnetic storms that peak every 11
years, causing electromagnetic disturbances on
the Earth.
• Streams of hot ionized gas that loop along the
sunspot’s field lines are called prominances.
Details
• The hot gases of the Sun are electrically
charged, so as it rotates magnetic fields are
formed.
• Since the Sun isn’t solid like a planet, its
equator rotates faster than its poles,
stretching the magnetic field lines deep in
the interior of the Sun.
• These get wrapped up, causing Sunspots.
In which century has sunspot
activity been the greatest?
Perhaps a Global Connection?
And More Details…
• Sometimes the energy in a prominence is so great
that it breaks free of the magnetic field and
escapes into space, adding to the Solar Wind.
• The Solar Wind is a constant stream of charged
particle blasting outward from the Sun.
• It is both a potential source of propulsion and
dangerous radiation.
• The Sun’s atmosphere, called the Corona, is a
superheated rarefied gas similar in composition
to the Solar Wind.
Formation
• The Sun condensed ~5 billion years ago out of an
enormous cloud of hydrogen, dust, and other
gases called a Bok Globule.
• As the globule contracted due to gravity, angular
momentum was conserved and the cloud spun
faster and faster, becoming a protostar.
• Small bits of the protostar were cast out, like
water in the spin cycle of a washer, to become the
Solar System.
• Bands of this debris condensed, or accreted, into
the planets, moons, and other denizens of nearby
space.
• For 9 Gyr (billion years) the Sun is pretty much as it is
now, though slowly increasing output
• At ~ 10Gyr the H in the core runs out and hydrostatic
equilibrium fails
• The Sun expands out to beyond the orbit of Venus as a
Red Giant
• Its He core contracts until it flashes into fusion at 100
million K.
• He burns in the core, H burns in a shell
• It will eject a large planetary nebula
• Left behind is its CNO core, known as a White Dwarf
The End of the Sun
• After 11 Gyr our Sun has
ceased to do fusion
• About the size of the
Earth, radiating due to
gravitational heating
• Super dense!
• Will exist as a white
dwarf for trillions of
years, cooling off and
becoming a black dwarf