Transcript Click here - Noadswood Science

Get into a group of 4
• 1 person in the group signs out a laptop.
• Log in.
• Open this power point in your class folder
• Studentshared/science/11x3
• You will today make a poster showing the life
cycle of stars.
• Everyone makes their own.
• There are 3 possible life cycles. In your group
make sure that you are showing all 3
lifecycles.
The Life Cycle of Stars
Stars form from clouds of Hydrogen gas ...
The force of gravity between all the atoms will result in
the cloud slowly contracting towards its centre.
Gravity
Gravity
Gravity
Gravity
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The result will be a dense ball of hydrogen, called a
Protostar.
As it contracts, the Gravitational Potential Energy of the gas
is converted into Heat, warming the Protostar.
If the Protostar has enough mass, the temperature and
density at the core will be enough for Fusion to begin, with
Hydrogen atoms combining to form Helium.
H
H
He
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The process of Fusion in the core generates heat, which
further warms the core and also warms up the outer layer
of Hydrogen.
Once Fusion starts the Protostar becomes a
Main Sequence Star.
H
H
He
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Over time, because of the Fusion process, the core becomes
more and more composed of Helium rather than Hydrogen.
The outer layer of the star will still be Hydrogen.
H
H
He
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As further time passes, the Hydrogen begins to run out.
The star will expand to become a
Red Giant or Red Super Giant
and Fusion will begin to generate heavier elements than
Helium.
What happens next depends on the mass of the star ….
If the star is small (up to 1.5 times the mass of our sun) the
fusion process in the core will finally run out of atoms to
process.
As less and less heat is generated in the Core the star
beings to cool down, and shrink in size.
The star will first shrink to become a
White Dwarf.
Then it will cool down to become a
Black Dwarf.
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But if the star is large (more than 1.5 times the mass of our
sun) the fusion process can continue to make large atoms
(up to Iron in the Periodic Table).
Once it begins generating Iron, the star will no longer be
able to produce enough heat in the core to remain stable.
The star therefore will explode in a
Supernova.
Leaving behind a super dense
Neutron Star.
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However if the star is more than three times the mass of
our sun, the Supernova will leave behind a
Black Hole.
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When a Supernova occurs, the outer part of the star (made
of Hydrogen) and part of the Core are spread out into space
and will cool.
This creates a cloud of Hydrogen gas, which (if big enough)
can form into a new star – starting the cycle again ….
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Important points:
• Fusion only occurs in a stars core, no Hydrogen is
converted to Helium in the outer layer
• The more massive the star, the faster the process of
fusion works (higher temperature and pressure in the
core);
• In generating heat via fusion, the mass of the star stays
roughly the same (unlike a fire which gets progressively
smaller, and a big star does not become a small star over
time);