Download Stars part 2

THIS PRESENTAION HAS BEEN RATED
TG-13
TEACHERS’ GUIDANCE STRONGLY ADVISED
Some Material May Be Unintelligible For Students Under 13.
Intense Frames of Scientific Instruction, Analysis, Comparing
and Contrasting, Description, and for Some Vocabulary.
BY THE
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ASTRONOMY
Stars
OBJECTIVES
By the end of this presentation, students will
be able to
• explain the role of nuclear fusion in the sun’s
core to release energy;
• communicate scientific ideas about the way
stars, over their life cycle, produce elements;
• illustrate the life span of the sun.
Stellar Formation and Life Cycle
Stars are theorized to evolve through
six stages of development…
The exact path of development
depends on the mass of the initial
interstellar gas cloud from which the
star forms.
Stellar Formation and Life Cycle
Photosphere
Convection
Zone
Radiation
Zone
Core
H-R DIAGRAM
A pattern of groups of stars emerge
when plotting the Abs. Mag. of a star
as a function of its temperature.
ABSOLUTE MAGNITUDE
Wolf-Rayet
-10
Stars-5
Hypergiants
Super Giants
Red Giants
0
+5
+10
+15
+20
White Dwarfs
30K
10K
7.5K
Red Dwarfs
6K
5K
TEMPERATURE (ºK)
3K
ABSOLUTE MAGNITUDE
RUSSELL-VOGT
THEOREM – the
H-R DIAGRAM
equilibrium
an ordinary
A
pattern of structure
groups ofofstars
emerge
star
is determined
byofitsa star
when
plotting the uniquely
Abs. Mag.
mass
chemical
as a and
function
of its composition.
temperature.
-10
-5
0
+5
+10
+15
+20
30K
10K
7.5K
6K
5K
TEMPERATURE (ºK)
3K
Stellar Formation and Life Cycle
Stars are theorized to evolve through
six stages of development…
1. Protostar Stage – the gravitational
collapse of a gaseous cloud mass.
• The collapse may be triggered by the
passing of, the eruption of, or the
explosion of a near-by star.
• Energy production is described by the
“Helmholtz Contraction”, where the heat
build up by the gravitational collapse.
Stellar Formation and Life Cycle
Stars are theorized to evolve through
six stages of development…
1. Protostar Stage
• Temperatures increase from -441°F to
1340°F.
• Out-lying gasses enshroud the new
protostar.
Stellar Formation and Life Cycle
Stars are theorized to evolve through
six stages of development…
1. Protostar Stage
• Large clouds subdivide into enormous
chunks while collapsing, forming a
protocluster.
• The protoclusters fragment into
individual protostars.
Stellar Formation and Life Cycle
Stars are theorized to evolve through
six stages of development…
2. Pre-Main Sequence Stage –
temperatures and pressures in the
center continue to rise, slowing the
rate of collapse.
• Energy production is described by
the “Helmholtz Contraction”.
Stellar Formation and Life Cycle
Stars are theorized to evolve through
six stages of development…
2. Pre-Main Sequence Stage
• Convection currents transport large
amounts of energy from the interior,
making the protostar visible and bright
for short periods at a time.
• Temperatures and pressures in the
core rise enough to initiate nuclear
reactions for energy production.
Stellar Formation and Life Cycle
Stars are theorized to evolve through
six stages of development…
2. Pre-Main Sequence Stage
• Brightness fluctuates (T-Tauri star),
until….
• Out-lying gasses (the COCOON
NEBULA) are blown away by the solar
wind of the new-burning star.
Stellar Formation and Life Cycle
Stars are theorized to evolve through
six stages of development…
3. Main Sequence Stage – a stable
state where pressures from energy
production in the core balance the
pressures from the gravitational
collapse of the shell.
• The more massive the star, the
faster it moves through this stage.
Stellar Formation and Life Cycle
Stars are theorized to evolve through
six stages of development…
3. Main Sequence Stage
• Energy production is described by
the Proton-Proton Chain.
21H → 2H + e+ + neutrino
2H + 1H → 3He + photon
3He + 1H → 4He + 21H + photon
• The more massive the star, the
faster it moves through this stage.
Stellar Formation and Life Cycle
Stars are theorized to evolve through
six stages of development…
3. Main Sequence Stage
• Energy production in larger stars is
described by the C-N-O Cycle.
• The more massive stars have greater
pressures and temperatures in the core
to produce heavier elements.
• the more massive the star, the faster it
moves through this stage.
Stellar Formation and Life Cycle
Stars are theorized to evolve through
six stages of development…
3. Main Sequence Stage (Larger Stars)
• The C-N-O Cycle:
12C + 1H → 13N + photon
13N → 13C + e+ + neutrino
13C + 1H → 14N + photon
14N + 1H → 15O + photon
15O → 15N + e+ + neutrino
15N + 1H → 12C + 4He + photon
Stellar Formation and Life Cycle
Stars are theorized to evolve through
six stages of development…
4. Giant Stage – The initial hydrogen fuel
in the stellar core lessens. Helium fission
intensifies and the shell expands
suddenly (Helium flash). A new position
of stability is reached after other periods
of expansion and contraction.
Stellar Formation and Life Cycle
Stars are theorized to evolve through
six stages of development…
4. Giant Stage –
• Larger, more massive stars may get
so hot and expand so rapidly, the
outer layers of the convection zone
are blown off as the inner layers over
expand, forming supergiants.
Stellar Formation and Life Cycle
Stars are theorized to evolve through
six stages of development…
4. Giant Stage –
• Energy production in the core is
described by the Triple Alpha Process:
4He + 4He → 8Be + photon
8Be + 4He → 12C + photon
Stellar Formation and Life Cycle
Stars are theorized to evolve through
six stages of development…
4. Giant Stage –
• The final phases of the Giant stage
are marked by still higher temperatures
and pressures in the core to synthesize
larger elements.
• Super and hyper giants can produce
all of the natural elements by nuclear
S-Process and R-Process reactions.
Stellar Formation and Life Cycle
Stars are theorized to evolve through
six stages of development…
5. Variable Stage – ionized helium
collecting on the newly expanded
surface of the convection zone
absorbs outgoing energy. Pressure
builds. The outer surface expands.
Energy is released. Surface subsides.
Process repeats.
Stellar Formation and Life Cycle
Stars are theorized to evolve through
six stages of development…
5. Variable Stage
• Some 28 different types if variable
stars.
Long period variable stars
Short period variable stars
Cephied variable stars
Irregular variable stars
Stellar Formation and Life Cycle
Stars are theorized to evolve through
six stages of development…
6. Terminal Stage - depending on the
initial mass of the star, it may either
1) fizzle out, forming a brown dwarf;
2) explode, blowing off the outer
photosphere and forming a smaller,
hotter white dwarf star;
Stellar Formation and Life Cycle
Stars are theorized to evolve through
six stages of development…
6. Terminal Stage –
3) explode and leave behind a dense
core, which is called a neutron star.
4) explode and leave behind a dense
core that collapses in on itself, which
is called a black star.
ASTRONOMY
Stars