Download Star Life Cycle - GSHS Mrs. Francomb

Life Cycle of Stars
Pumbaa: Timon?
Timon: Yeah?
Pumbaa: Ever wonder what those sparkly dots are up there?
Timon: Pumbaa. I don't wonder; I know.
Pumbaa: Oh. What are they?
Timon: They're fireflies. Fireflies that uh... got stuck up on
that big... bluish-black... thing.
Pumbaa: Oh. Gee. I always thought that they were balls of
gas burning billions of miles away.
Timon: Pumbaa, wit' you, everything's gas.
A Star is Born
• Stars are born in nebulae. Huge clouds of
dust and gas collapse under gravitational
forces.
• As the cloud collapses the temperature
increases and a protostar is formed.
• These young stars undergo further collapse,
becoming hot enough to fuse hydrogen into
helium as main sequence stars.
Looking at the Birthplace of Stars
• Horsehead Nebula
• Rosette Nebula
Everything Depends on Mass
• The more mass a star starts out with, the
brighter and hotter it will be.
• The color of the star depends on the surface
temperature of the star.
• Its temperature depends on its mass, or how
much gas and dust were accumulated during
formation.
The Constant Battle Against Gravity
• Gravity is always
present, compressing
stars toward their center
of mass.
• Nuclear Fusion is the
force that acts against
gravity, releasing energy
outwards
Adolescent Stars
• The force of gravity is pulling in on the star
while the radiation from fusion is pushing
out.
• The star is burning its most abundant fuel,
HYDROGEN!
Nuclear Fusion
•
•
•
•
•
•
•
Conservation of Mass and Energy E = mc2
Nucleus 1 + Nucleus 2
Nucleus 3 + Energy
Proton - Proton Chain Reaction
1H + 1H
2D + Energy
2D + 1H
3He + Energy
3He + 3He
4He + 1H + 1H + Energy
After a while all the Hydrogen gets turned into
He and lots of energy has been released.
Red Giants
• After millions to billions of years, depending on their initial
masses, stars run out of their main fuel - hydrogen.
• Without the outward pressure generated from these reactions
to counteract the force of gravity, the outer layers of the star
begin to collapse inward toward the core.
• Just as during formation, when the material contracts, the
temperature and pressure increase.
• This newly generated heat temporarily counteracts the force
of gravity, and the outer layers of the star are now pushed
outward.
• The star expands to larger than it ever was during its lifetime
-- a few to about a hundred times bigger.
Planetary Nebula
• After expanding and reaching the enormous red giant
phase, the outer layers of the star continue to expand.
• The core contracts; the helium atoms in the core fuse
together, forming carbon atoms and releasing energy.
• The core is now stable since the carbon atoms are not
further compressible.
• Now the outer layers of the star start to drift off into
space, forming a planetary nebula (a planetary nebula
has nothing to do with planets).
• The star loses most of its mass to the nebula.
Egg Nebula formed only a few hundred years ago.
It takes light about 3000 years to reach us from the Egg Nebula.
White Dwarf
• The star is now a white dwarf, a stable star
with no nuclear fuel. It radiates its left-over
heat for billions of years.
• When its heat is all dispersed, it will be a
cold, dark black dwarf - essentially a dead
star (perhaps full of diamonds, highly
compressed carbon).
A white dwarf in the M4 Globular Cluster
SUPERNOVA:
A star that dramatically
increases in brightness because of an explosion on its surface.
• Means “new” in Latin but is actually the
death of a star.
• Here’s a before and after picture of a nova
in 1992.
A Closer Look
H-R Diagram
Our Star the Sun.
• Diameter 1.4 x 106 km
• Mass 2.0 x 1030 kg (300,000 times bigger
than the Earth).
• On the H-R Diagram our sun is a yellow
star in the main sequence.
• In about 5 billion years our Sun will start to
become a Red Giant
Chemistry and the Sun
Element
Hydrogen
Helium
Oxygen
Carbon
Nitrogen
Silicon
Magnesium
Neon
Iron
Sulfur
Abundance
(% of total # of atoms)
91.2
8.7
0.078
0.043
0.0088
0.0045
0.0038
0.0035
0.0030
0.0015
Abundance
(% of total mass)
71.0
27.1
0.97
0.40
0.096
0.099
0.076
0.058
0.140
0.040