Transcript Star Life Cycle Powerpoint

The Life Cycle of Stars
A Note Taking Experience.
Cycle for all stars
• Stage One- A star is born in a vast, dense
cloud of gas, mostly hydrogen and helium,
and dust called a Nebula.
• Stage Two - As a nebula collapses, gravity
pulls the hydrogen gas in the nebula
together and it begins to spin; as the gas
spins faster, it heats up and is known as a
Protostar.
• Once a protostar forms and the temperature
reaches 15,000,000 degrees Celsius, a star
turn hydrogen into helium within its Core
by Nuclear Fusion.
• Stage Three - The cloud begins to glow
brightly and at this temperature it contracts
and becomes stable as a Main Sequence
Star/Yellow Star. Our Sun is in this stage
right now.
• As the Main Sequence Star glows, hydrogen
in the core is converted into helium by
Nuclear Fusion.
http://www.waowen.screaming.net/revision/universe/msstar.htm.
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http://www.waowen.screaming.net/revision/universe/redgiant.htm
Hydrostatic Equilibrium
• In a steadily burning star on
the main sequence, the
outward pressure of hot gas
exactly balances the inward
pull of gravity. This is true
at every point within the
star, guaranteeing its
stability.
• Stage Four - When the hydrogen supply in
the core begins to run out, the core becomes
unstable and contracts; the outer shell of the
star which is still mostly hydrogen, starts to
expand. As it expands, it cools and glows
red; it has now reached the Red Giant
Phase.
Mass of Star Determines Fate
• All stars evolve the same way up to the Red
Giant Phase. The amount of mass a star has
determines which of the following life cycle
paths it will take after the Red Giant Phase.
• Small Stars
• Massive Stars
Fate of Small Stars
• Stage Five- Helium atoms in the core fuse
to form carbon atoms; the hydrogen gas in
the outer shell is blown away to form a ring
around the core called a Planetary Nebula
• Stage Six- Gravity causes the last of the
star’s matter to collapse inward and
compact into an extremely dense White
Dwarf core that glows with a white hot
light.
• Stage Seven - Once all of a white dwarf’s
energy is gone, it no longer emits light,
reaching the Black Dwarf phase in which it
will forever remain. A completely dead star
that is dark and cold.
• This is the end of a small star’s life.
Fate of a Massive Star
• In the next million years, a series of nuclear
reactions occur forming a carbon atoms
from the fusion of helium atoms; gravity
continues to pull carbon atoms together as
the temperature increases forming oxygen,
nitrogen, and eventually iron. GETTING
HEAVY!
• Stage Five - Fusion stops and the iron
atoms start to absorb energy; this energy is
eventually release in a powerful explosion
called a Supernova; a supernova can light
up the sky for weeks.
• Stage Six a - The core of a massive star that
is 1.5 to 4 times as massive as our Sun ends
up as a Neutron Star after the
supernova;neutron stars spin rapidly giving
off radio waves emitted in pulses, these
neutron stars are called Pulsars.
• Stage Six b - The core of a massive star that
has 8 or more times the mass of our Sun
remains massive; no nuclear fusion takes
place to support the core, so it is swallowed
by its own gravity becoming a Black Hole.
HR Diagram