Transcript Document

PASS Content Standard 5.2
All stars have a life cycle including birth,
development, and death. Fusion reactions
in the stars release great amounts of
energy and matter over millions of years.
A star's life cycle
is determined by
its mass.
The larger its mass,
the shorter its
life cycle.
The star's mass is
determined by the
amount of matter
available in the
giant cloud of gas
and dust, nebula,
from which it forms.
QuickTime™ and a
Sorenson Video 3 decompressor
are needed to see this picture.
Nebulae - 5 min
Stage 1
Dust and gas are
pulled together by
gravity to form a
protostar inside
the nebula.
The contraction
causes heating
to begin.
Stage 2
When the star is
hot enough, about
o
15,000,000 C,
nuclear fusion
begins in the core
of the star, and it
begins to emit
light and heat.
Stage 2
At this point, the
star has become
a Main Sequence
star.
Stage 3
After millions of
years, the star
runs out of
hydrogen in its core.
The core becomes
unstable and
contracts, while the
outer shell starts
to expand.
Stage 3
The star has now
become a red giant.
When our Sun
becomes a red
giant, it will expand
as far as the orbit
of the Earth.
Stage 4
Stage 4 has two
possibilities,
depending on the
mass of the star.
Stage 4 (low mass)
A star like our Sun
will contract,
becoming a white
dwarf, which slowly
cools, changing
color as it does,
until it can no
longer be seen a black dwarf.
Stage 4 (high mass)
More massive stars
may glow brightly
again as they
undergo further
fusion reactions,
expanding and
contracting
several times...
Stage 4 (high mass)
and forming the
nuclei of heavier
elements before
becoming a
supernova.
Stage 4 (high mass)
A supernova is an
exploding star that
throws its outer
layer of dust and
gas into space,
leaving behind a
very dense core
called a
neutron star.
Stage 4 (high mass)
If the star is very
massive, roughly
3 or more times the
mass of our Sun,
the final object
produced may be
a black hole.
Stage 4 (high mass)
The dust and gas
left behind by a
supernova,
supernova remnant,
can be the raw
material used to
produce new stars.
Stage 4 (high mass)
Stars formed from
the remains of
supernovae are
called Second
Generation stars.
Our Sun is a
second generation
star.
Unlike chemical
reactions,
nuclear reactions
involve the nucleus
of the atom.
Nuclear reactions
release many times
the energy of
chemical reactions.
There are two
types of nuclear
reactions.
Fission is a
nuclear reaction
in which a heavy
nucleus is split
into two fragments.
This picture is of
a ground explosion
of 20 pounds of
plutonium,
releasing the
energy equal to
70 million pounds
of TNT.
A fusion reaction is one in which two
or more small nuclei are forced
together to form one larger nucleus.
This is a picture of a "fusion"
reaction equal to 2,180 million
pounds of TNT.
Fusion reactions power
the stars, converting
hydrogen into helium.
Temperatures in the core
o
of our Sun (over 15 million C)
are high enough to produce
nuclei up to the size of iron,
(atomic mass 56).
To produce nuclei heavier
than iron requires
temperatures only found
in supernova explosions,
o
(over 100 Billion C).