Download 15. Our Star

The Sun, Our Star
&
The Origin of Atoms
Solar Telescope Outside Class:
Light filter used:
Hydrogen emission passes to camera.
Reveals Chromosphere.
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Announcements
• Telescope open tonight at
8:30pm : last night !
• Homework due Friday on
Extrasolar planets (Chap. 13)
• Both Observation Reports
also due Friday.
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Composition of the Sun
(by Mass)
C, N, O, Fe: 1%
He
28%
H
He
O
C 0.3%
Fe 0.2%
Hydrogen 70%
Magnesium
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Sodium
Layers of the Sun
Solar
Wind
photosphere
Convective
Zone
Core
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Radiation
Zone
Photon Transport of Energy
“Radiation Transport”
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Energy Transport by Photons (Light)
• Radiation Zone
• Energy travels as photons of light, which continually collide with particles
• Photons scatter, changing direction (random walk), and change wavelengths
• This is called radiative diffusion
Path of photon,
scattered by electrons
and atoms.
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• This is a slow process!
• It takes about 1 million
years for energy to
travel from the core to
the surface.
Layers of the Sun
Solar
Wind
photosphere
Convective
Zone
Core
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Radiation
Zone
Convective Transport of Energy
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Wait 10 sec
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Convective Energy Transport
• Convection: Hot air rises; carries heat with it.
• The bottom of the convection zone is heated … hot gas rises to the top
• cooler gas sinks to the bottom…similar to boiling a pot of water!
• Energy is brought to the surface via bulk motions of matter
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Convection Visible at
Surface of the Sun
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Layers of the Sun
Solar
Wind
photosphere
Convective
Zone
Core
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Radiation
Zone
Photosphere
• T = 5,800 K; depth = 400 km
• This is the yellow “surface” that we see.
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The Photosphere:
Visible Surface of the Sun
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• Photosphere:
opaque “surface”
human eye sees.
• Granulation
(convection)
• Sunspots
Journey Into the Sun
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•
•
•
•
Photosphere
Convection Zone
Radiation Zone
Core: proton-proton
nuclear reactions:
Helium
Photospheric Features
Sunspots: dark spots on the surface where
the temperature is cooler.
Granulation: the
tops of convection
cells seen “bubbling”
on the Solar surface
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National Solar Observatory/AURA/NSF
Sunspots and Convection at
Surface of the Sun
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Layers of the Sun
Solar
Wind
photosphere
Convective
Zone
Core
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Radiation
Zone
Solar Chromosphere
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Chromosphere
Temp = 10,000 K
Hydrogen Emission
n = 3 to 2.
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Chromosphere
• T = 10,000 K;
• Depth: Thin and patchy over surface
• A thin hot layer above the photosphere
where most of the Sun’s UV light is emitted.
• UV image of the Sun
Light emitted from
Helium at 20,000 K
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SOHO
Prominences from the Chromosphere
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Hydrogen Alpha:
Electrons drop from
3rd - 2nd level.
Wait 10 sec
For movie.
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Prominences – Gas trapped in the magnetic fields is heated
and elevated above the photosphere and chromosphere.
X-ray images from NASA’s TRACE mission.
Movie. Click to launch.
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Solar Prominences: Magnetic Ejections
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Solar Flares: Magnetic Explosions
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Solar Flares: Magnetic Explosions
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The Corona
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Corona
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Corona
• T = 2 Million K
• Thickness  Radius of Sun (700,000 km)
• The hot, ionized gas which surrounds the Sun.
– it emits mostly X-rays
• It can be seen in visible light during an eclipse.
X-ray image (YOHKOH telescope)
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Visible image
Coronal Mass Ejections
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Solar Wind
• The stream of electrons, protons, Helium nuclei and
other ions which flow out from the Sun.
• It extends out beyond Pluto.
X-ray image of corona
UV image of solar wind
Visible image of solar wind
comet SOHO-6 (fell into Sun)
Sagittarius
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Solar Wind
electrons, protons, He nuclei expelled by flares
Interact with Earth’s magnetic field to cause…
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The Aurorae
the Northern & Southern Lights
• A strong Solar
wind can affect
human technology
by:
• interfering with
communications
• knocking out
power grids
• damage electronics
in space vehicles
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Solar Magnetic Activity
• The photosphere of the Sun is covered with sunspots.
• Sunspots are not constant; they appear & disappear.
• They do so in a cycle, lasting 11 years.
• Sun’s magnetic field switches polarity (N-S) every 11 yrs
• So the entire cycle repeats every 22 yrs
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Sunspots: Cool, Magnetic Regions
Umbra, Penumbra
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What causes a sunspot?
Magnetic field
slows down
convection;
Less heat is
transported to
surface;
so that part of
photosphere is
cooler
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11-year Sunspot Cycle
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Magnetic Activity changes with Time :
11-year Cycle (Last Maximum in Year 2000)
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Sunspot Cycle
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Magnetic Fields:
Winding up, tangling in 11 years
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Rotation Period of Sun: 30 days
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The Sun:
How long will it Shine ?
Until it burns up its available Hydrogen
(in the core where T > 2 million degrees)
At Current Rate of Energy production:
5 billion more years
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The Death of the Sun
in 5 Billion Years
• Core becomes pure helium! No Hydrogen burning possible.
• The Helium core begins to collapse.
– H shell (around Helium) heats up and H fusion begins there.
– Outer layers of the Sun expand.
– The Sun enters giant phase of its life.
Original Sun
Expanding:
“Giant Star”
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The Dying Sun: 5 billions years from now
Giant Star Phase
• The He core collapses until it heats to 108 K
– He fusion begins ( 3 He
•
C)
Carbon forms!
The star, called a Giant, is once again stable.
–
–
Gravity balanced by pressure, from He fusion reactions
Giant stars create, and release, most of the Carbon in the
universe: Key ingredient for organic molecules and life.
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Fusion of 3 helium nuclei
into Carbon
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“ Triple-Alpha “
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Planetary Nebula
• When the Giant star exhausts its Helium fuel in the central core:
– the Carbon core collapses.
– Low & solar-mass stars don’t have enough gravitational energy to heat to
6 x 108 K (temperature where Carbon fuses)
• The He & H burning shells produce huge amounts of energy.
• The energy blows away the star’s outer layers of gas:
• Making a “planetary nebula”.
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Planetary Nebulae
Cat’s Eye Nebula
Twin Jet Nebula
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Planetary Nebulae
Ring Nebula
Hourglass Nebula
The collapsing Carbon core becomes a White Dwarf
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When High Mass Stars Die:
Supergiants
They exhaust H fuel.
He C .
• They Contract, heat up to
600 million K.
– C fuses into O.
• C is exhausted, core
collapses until O fuses.
• The cycle repeats itself.
–
–
–
–
O burns to Ne.
Ne burns to Mg.
Mg burns to Si.
Si burns to Fe.
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Supernova
• The mass of the iron (Fe) core increases
- No nuclear reactions: no energy production!
– Gravity overwhelms the gas pressure
– Electrons are smashed into protons  neutrons
•
The neutron core collapses until
abruptly stopped by neutrinos
flying outward!
– this takes only seconds
– The core recoils, bounces, and
neutrinos force the gas outward in
an explosion.
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Supernova Explosions
The explosion brings
temperature to
Billions of degrees:
The elements heavier
than Fe are instantly
created
Crab Nebula in Taurus
supernova exploded in 1054
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Four supernovae have
been observed in our
part of the Milky Way
Galaxy:
1006, 1054, 1572, &
1604
Supernovae
Tycho’s Supernova (X-rays)
exploded in 1572
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Veil Nebula
The Origin of the Atomic Elements
The 92 atomic elements were all
constructed in the centers of stars
(except hydrogen, helium and lithium).
Where did all the
Hydrogen and Helium
Come from?
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•
•
•
•
•
Explosion: Hot and Dense. Over a trillion degrees.
Time and Space Created.
Universe expands ever since. Accelerating now.
Science can not describe what happened
13.5 Billion Years Ago.
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before the Big Bang.
t < 0.001 sec
• Quarks and Electrons as numerous as photons.
(No Protons or neutrons: At billions of degrees,any
protons collide, break apart into quarks.)
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Quarks and Photons Annihilate:
Equilibrium
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t < 0.001 sec
• Quarks and Electrons as numerous as photons.
• T > 0.001 sec:
Quarks combined to form protons & neutrons
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Protons and Neutrons
Are Composed of 3 Quarks
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Era of Nucleosynthesis
(t < 3 min)
• Protons & neutrons fuse !
4p
He
• Some He nuclei torn apart by the high temperatures
9
• When Universe was 3 min old, it had cooled to 10 K.
• At this point, the fusion stopped
• Afterwards, the matter in the Universe was:
• 75% Hydrogen nuclei (i.e. individual protons)
• 25% Helium nuclei
• trace amounts of Deuterium (H isotope) & Lithium nuclei
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The Universe since the Big Bang: Gravitational Attraction of material
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Billions
ofInc.,
years
ago as Addison-Wesley
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Era of Galaxies ( t >
9
10
yr)
• The first galaxies came into existence about 1 billion
years after the Big Bang.
• This is the current era of the Universe.
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• Time and Space Created.
• 13 Billion Years Ago.
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• Hot and Dense : Over a trillion degrees.
• Science can not describe what happened before the Big
Bang.
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2005 Pearson Education Inc., publishing as Addison-Wesley
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Luminosity “Standard Candles”
Marking Distance in the Universe
Type Ia Supernova
White Dwarf
An explosion resulting from the thermonuclear
detonation of a White Dwarf Star
•
•
Giant Stars spilling mass onto white dwarfs
White dwarfs explode when Mass > 1.40 MSUN
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The life of a Supernova Ia
On the Rise for 6 days
Age:
-6 days
Maximum
+26 days
+47 days
+102 days
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Decline for 79 days
“Standard” Candles
Hubble’s Diagram
dust
Bright = near
dim = far
dim & red=closer!
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The Dim,
the Distant
and the Dusty
Improved SN Ia distances
reveal motion of Local Group,
constrains
< 0.5 from flows
Riess
et al 1995,1997
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Pearson
Education Inc., publishing as Addison-Wesley