STARS
Amole
Spectra of Science
2013
What are Stars?
• A large celestial body of hot gas that
emits light
• Greeks grouped stars in patterns
called constellations
• Use the unit light-year to measure
distances between stars
– 9.5 x 1015 m
• Driven by nuclear fusion reactions
Why do Stars look Different from
One Another?
•
•
•
•
Size
Distance from Earth
Temperature
Stage of Life Cycle
Characteristics of Stars
• Color indicates
temperature
– Blue (Short λ) = Hot
– Red (Long λ) = Cool
– The hotter they are the
faster they burn out
• Magnitude
– Brightness
– Smaller numbers
represent brightest stars
Classification of Stars
• Classified by temperature and brightness
• Decreasing Temperature and brightness
• 
• Oh, Be A Fine Girl, Kiss Me
Classification of Stars
Class
Temperature
Color
O
20,000- 60,000 K
Blue
B
10,000 – 30,000 K
Blue-white
A
7,500 – 10,000 K
White
F
6,000 – 7,500 K
Yellow-white
G
5,000 – 6,000 K
Yellow
K
3,500 – 5,000 K
Orange
M
2,000 – 3,500 K
Red
H-R Diagram
Nuclear Fusion
• Strong gravitational
forces hold stars
together
• Energy from fusion
creates outward
pressure balancing
inward pull
• Hydrogen atoms are
fused to form helium
Layers of Stars
•Energy moves through
layers by radiation and
convection
•May take millions of
years for energy to work
its way through star to
surface
•After leaving the surface
it enters space traveling
at the speed of light,
3 x 108 m/s
Temperatures of the Sun
What Happens When a Star Runs
out of H?
• Begins to fuse
He
• Then, a
succession of
heavier elements
• Iron is the most
stable; it requires
energy verses
creating it
• Star begins to
die
Life Cycle of Stars
Stellar Nebula
• Nebulas are clouds of
dust and gas from
which stars are born
– Grains of carbon and
silicon
• Matter compresses due
to own gravity
• Temperature and
pressure slowly
increase from
compaction
Omega Nebula
Eagle Nebula
Lagoon Nebula
Bubble Nebula
Crescent Nebula
Orion Nebula
Crab Nebula
Adult Star
• Actively undergoing
hydrogen fusion
• Main Sequence star
• Spends most of its
lifetime in this phase
• 90% of stars in the
galaxy are in this
phase
• An average size like
our sun will “burn”
much longer than a
larger, more massive
star
Red Giants and Supergiants
• When a star runs out
of hydrogen, it begins
to die
• Energy from fusion no
longer counteracts
gravity, and the core
collapses
• Causes outer layers
to expand
• Average stars create
Red Giants
• Massive stars create
Red Supergiants
White and Black Dwarfs
• Core runs out of He,
and is no longer able
to fuse the remaining
heavier elements
• The star blows its
outer layer away
• The core remains
behind and burns as a
white dwarf
• Eventually it cools to
become a black dwarf
Little Ghost Nebula
Stingray Nebula
Ring Nebula
Supernova
• Massive stars
end in violent
explosions that
blow away the
outer layers of
the star
• These stars
result in either a
neutron star or
supernova
Neutron Star
• Leftover core has
between 1.4 – 3 solar
masses
• Collapses so much that
protons and electrons
combine to form neutrons
• Very dense (a thimbleful
weights more than 100
million tons)
• Emit radio waves
(pulsars)
Black hole
• Leftover core has a mass greater than 3
solar masses
• Collapses so much that not even light can
escape its gravity
Milky Way Black Hole
Death of a Star Simulations
Life Cycle of Stars