Download Star Properties and Stellar Evolution

Star Properties and
Stellar Evolution
What are stars
composed of?
Super-hot gases of
Hydrogen and
Helium. The sun
is 70% Hydrogen
and 30% Helium.
What is the mass of
stars?
A star’s mass is compared to
the sun’s mass. This is
called a solar mass. Mass
varies form .1 solar masses
to >10 solar masses.
What is the size of
stars?
Vary from the size of Earth
to 2,000 times the size of the
sun.
What determines the
color of a star?
Surface Temperature
Hot stars are blue-white
Cool stars are red
What is Luminosity?
It is the actual
brightness of a star.
Depends on size and
temperature.
What is Apparent
Magnitude?
How bright a star appears to be
from the Earth. Depends on
distance.
Measuring Magnitude
The magnitudes of the brightest
stars are negative. Each number
of magnitude equals a 2.5
difference from the previous
number.
Examples
Sirius = -1.44
Sun = -26.8
Betelgeuse = +0.45
Moon = -12.6
How can stars of
different distances be
compared?
Use their brightness
if they were all an
equal distance from
Earth = 32 ly.
Absolute Magnitude
Why do some stars
change in brightness?
Variable Stars
1. Pulsating stars – expand and contract
2. Cepheid Variables – used to find
distances to galaxies that contain them
3. Eclipsing Binaries – 2 stars revolve
around each other
Stellar Evolution
NEBULA
Clouds of gas and
dust where stars are
born. Cloud
contracts and heats
up.
Stellar Evolution
Protostar
Large glowing cloud
sections that will
eventually become
stars.
Stellar Evolution
At 10 million
Main Sequence degrees, fusion
begins and a star in
born. It is in
equilibrium. The sun
is an example of this
type of star.
Stellar Evolution
Red Giant
H is depleted. He
begins to fuse. Star
expands and outer
edges cool and
become red. (large,
red cool = old stars)
Stellar Evolution
stars less than 4x size of sun
White Dwarf
H and He fuel gone.
Collapses to size of
Earth.. Glows faintly,
dim, hot, and small.
Stellar Evolution
stars less than 4x size of sun
Nova
White dwarf flares
up and brightens for
a few years, then
fades.
Stellar Evolution
stars larger than 4x size of sun
Supergiant
Red giants grow
seven larger and
becomes
yellow/orange.
Stellar Evolution
stars larger than 4x size of sun
Supernova
Star explodes
violently! Large
Magellanic Cloud in
1987 – 170,000 ly
away.
Stellar Evolution
stars larger than 4x size of sun
Neutron Star
Core of supernova.
So dense that 1 tsp =
billion tons.
Stellar Evolution
stars larger than 4x size of sun
Black Hole
Objects so dense that
gravity will not
allow even light to
escape. Look for xrays, black area,
gravity pulling
matter in.
Nebula
Protostar
Main
Sequence
Red Giant
Less than 4 solar masses
White
Dwarf
Greater than 4 solar masses
Super
giant
Supernova
NOVA
Neutron Star
Black Hole
Stars are classified using surface temperature and
absolute magnitude.
Animation of HR Diagram
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