Transcript CH27.2 Stellar Evolution

Date:_____________
Topic:____________
Stellar
Evolution
CH 27 Section 2
A typical star exists for billions of years, making it
impossible for astronomers to study a single star through it’s
entire life.
Astronomers developed Theories –scientifically acceptable
explanations for observed facts.
Through the years, scientists have developed a
theory on the life of stars……starting with A……
N
E
B
U
L
A
NEBULA – birthplace
of a star, about 70%
hydrogen, 28% helium
and 2% “heavier
elements”
The process of a
star’s “birth” is
thought to begin
with the explosion of
a nearby star,
causing a sphere of
matter to build at
the center of the
nebula. As
gravitational forces
increase, the nebula
becomes smaller and
spins faster.
Protostar – 2nd step in the evolution of a
star. The center of a shrinking, spinning
nebula.
Temperature begins to increase at the center, due to:
1. The collision of particles.
2. Increased pressure.
At a temperature of 10,000,000 degrees Celsius
NUCLEAR FUSION begins and the PROTOSTAR
begins to generate energy. THEN it is considered to
be a star.
A nebula may produce
more than one star…………..
and is thought to be
where planets develop,
revolving around a central
star.
MAIN SEQUENCE STARS – Longest stage in the life of a star.
MUCH ENERGY IS GENERATED IN THIS PHASE
The process of FUSION releases enormous amounts of energy!
When 1 gram of Hydrogen is converted into Helium,
enough energy is released to light a 100 watt light-bulb
for 3,000 years.
10 times the size of the
sun
Giants and
100 times the size
Supergiants of the sun
-3rd
stage of a star
- when almost all the hydrogen has
been fused to helium.
The core of the star contracts causing
higher temperatures and the helium to be
fused into carbon atoms.
White Dwarf stars – the end of helium
fusion
A hot dense core is all that remains and can
“shine” for billions of years before
completely cooling.
-the core heats and illuminates(lights) the
remaining gases
- these gases appear as a PLANETARY
NEBULA
Black Dwarf
- when a white dwarf no longer emits energy
- “dead star”
NONE are yet known to exist…..our universe
isn’t thought to be old enough for this to
happen yet!
NOVA
Not all white dwarfs just cool and die.
Some may have one or more large
explosions, causing them to become
very bright for a short time(days)
-explosive release of energy, gas and
dust into space
SUPERNOVA
-when a large star(10-100 times
the size of the sun) has such a
large explosion that it blows
itself up.
The largest known release of energy in the
universe. Can be seen for weeks.
In 1054 Chinese astronomers saw an explosion that
was so bright it could be seen during the day for
three weeks!
Neutron Star
-incredibly dense ball of
neutrons left
over after a supernova explosion
- some emit(give off) two beams that
sweep across space –called PULSARS
Black Holes
-leftovers from some massive stars
-extreme gravity – keeps light from
escaping
VERY difficult to detect(see). Today black holes
are thought to be at the cores of many galaxies.