Transcript The Sun is a mass of Incandescent Gas

The Sun is a mass of
Incandescent Gas
A gigantic nuclear furnace
It’s reasonable to assume the sun
is on Fire
• Until you do the math, which shows it
would burn out in a few million years.
• By 1850, the Earth already was starting to
look A LOT older than that – billions of
years old
Hans Bethe worked out the details
around 1930
• When H + H fuses into He under
tremendous heat caused by the squeeze
of gravity, a tiny amount of mass is
converted into an enormous amount of
energy, enough to last a LONG time.
• The actual reactions are numerous and
more complex
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1H
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3He
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+ 1H --> 2H + antielectron + neutrino
1H + 1H --> 2H + antielectron + neutrino
electron + antielectron --> photon + photon
electron + antielectron --> photon + photon
2H + 1H --> 3He + photon
2H + 1H --> 3He + photon
3He + 3He --> 4He + 1H+ 1H
+ 4He --> 7Be + photon
– 7Be = (4 p + 3 n)
7Be + electron --> 7Li + neutrino
– 7Li = (3 p + 4 n)
7Li + 1H --> 2 4He
alternatively
– 7Be + 1H --> 8B + photon
• 8B = (5 p + 3 n)
– 8B --> 2 4He + antielectron + neutrino
start with 12C
– 12C = (6 p + 6 n)
12C + 1H --> 13N + photon
– 13N = (7 p + 6 n)
13N --> 13C + antielectron + neutrino
– 13C = (6 p + 7 n)
13C + 1H --> 14N + photon
– 14N = (7 p + 7 n)
14N + 1H --> 15O + photon
– 15O = (8 p + 7 n)
15O --> 15N + antielectron + neutrino
– 15N = (7 p + 8 n)
15N + 1H --> 12C + 4He
Stars are born in a region of high density Nebula,
and condenses into a huge globule of gas and
dust and contracts under its own gravity.
A region of condensing matter will begin to heat
up and start to glow forming Protostars. If a
protostar contains enough matter the central
temperature reaches 15 million degrees C.
At this temperature,
nuclear reactions in
which hydrogen fuses
to form helium can
start.
The star begins to
release energy,
stopping it from
contracting even more
and causes it to shine.
It is now a Main
Sequence Star.
Equilibrium
Gravity
Gravity
Gravity
Gravity
Gravity
Radiation
Energy
Gravity
Gravity
Gravity
Gravity
The Sun and other
stars are really only
roughly in
equilibrium. The
Sun is extremely
dynamic, and has
storms larger than
the Earth.
Some of these storms reach as far as
the Earth and inrushing energetic
protons interact with the Earth’s
magnetic field and atmosphere to
cause the Aurora. The sun, then, is a
source of low energy Cosmic Rays.
A small star of one solar mass remains in
main sequence for about 10 billion years,
until all of the hydrogen has fused to form
helium.
The helium core now starts to contract
further and reactions begin to occur in a
shell around the core.
The core is hot enough for the helium to
fuse to form carbon. The outer layers begin
to expand, cool and shine less brightly. The
expanding star is now called a Red Giant.
In the next million years a series of nuclear
reactions occur forming different elements in
shells around the iron core.
This is the factory where all elements heavier
than Lithium are made, including the atoms
important for life: Oxygen, Iron, Carbon, etc.
EVERY Iron atom in your
body was made in a
SUPERNOVA
The helium core runs out, and the outer
layers drift of away from the core as a
gaseous shell. This gas that surrounds the
core is called a Planetary Nebula.
The remaining core (80% of the original star) is
now in its final stages. The core becomes a
White Dwarf. The star eventually cools and
dims. When it stops shining, the now dead star is
called a Black Dwarf.
Massive Stars: more than 10 Solar Masses
Massive stars have a mass 3x times that of the
Sun.
Some are 50x that of the Sun!
Massive stars evolve in a similar way to a small
stars until it reaches its main sequence stage
(see small stars, stages 1-4). The stars shine
steadily until the hydrogen has fused to form
helium ( it takes billions of years in a small star,
but only millions in a massive star).
The massive
star then
becomes a
Red
Supergiant
and starts of
with a helium
core
surrounded by
a shell of
cooling,
expanding gas
Eventually, Fusion
reactions run out of
fuel, and gravity
overcomes radiation.
The core collapses in
less than a second,
causing an explosion
called a Supernova, in
which a shock wave
blows of the outer
layers of the star. (The
actual supernova
shines brighter than an
entire galaxy for a short
time).
These explosions are what distributes
heavier atoms across the universe.
Atoms, small fragments of those
explosions, reach the Earth constantly,
and are generically called High Energy
COSMIC RAYS.
Shockwaves from these explosions
compress gas clouds, giving rise to the
gravitational nucleus of new stars.
Sometimes the core survives the explosion. If the surviving core is
between 1.5 - 3 solar masses it contracts to become a a tiny, very
dense Neutron Star. If the core is much greater than 3 solar masses,
the core contracts to become a Black Hole.
The famous
HertzsprungRussell
diagram
compares a
star’s mass and
luminosity, and
is used to
classify stars
and determine
their future
paths.