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Star Life Cycles
We Classify Stars by Their
Characteristics
All stars are huge
balls of glowing
gas that produce
or have produced
energy by fusion
Stars differ in
size, brightness,
and temperature
We Classify Stars by Their
Characteristics
Stars look like small
points of light
because they are
very far away
Light-year – the
distance light travels
in one year
Brightness and Distance
The amount of light a
star gives off and its
distance from Earth
determines how bright it
appears to an observer
Parallax – the apparent
shift in the position of an
object when viewed from
different locations
Size
Giant and supergiant
stars range from ten
to hundreds of times
larger
Because giant and
supergiant stars have
such huge surface
areas to give off light,
they are very bright
Size
Stars called white
dwarfs are about
100 times smaller in
diameter than the
Sun, or roughly the
size of Earth
White dwarfs cannot
be seen without a
telescope
Color and Temperature
If you observe
stars closely, you
may notice that
they vary slightly in
color
The differences in
color are due to
differences in
temperature
Color and Temperature
The coolest stars
are red - the
hottest stars are
blue-white
The colors and
lines in a spectrum
reveal which gases
are present in the
star’s outer layers
Stars Have Life Cycles
Although stars last for
very long periods, they are
not permanent
The life cycle of a star
varies, depending on the
mass of the star
Stars form inside a cloud
of gas and dust called a
nebula
Stars Have Life Cycles
Gravity pulls gas and dust
closer together in some
regions of a nebula – as the
matter contracts, it forms a
hot, dense sphere – the
sphere becomes a star if its
center grows hot and dense
enough for fusion to occur
When a star dies, its matter
may eventually become part
of new stars
Stages in the Life Cycles of Stars
Lower-Mass Stars
– The stage in which stars
produce energy through
the fusion of hydrogen
into helium is called the
main sequence
– When a lower-mass star
runs out of hydrogen, it
expands into a giant
star, in which helium
fuses into carbon
Stages in the Life Cycles of Stars
– Over time a giant star
sheds it outer layers
and becomes a whitedwarf – the dead core
of a giant star
– Although no fusion
occurs in white
dwarfs, they remain
hot for billions of
years
Stages in the Life Cycles of Stars
High-Mass Stars
– Stars more than eight times as
massive as our Sun spend
much less time in the mainsequence stage because they
use their fuel rapidly
– After millions of years, a
higher-mass star expands to
become a supergiant star –
fusion produces heavier and
heavier elements
Stages in the Life Cycles of Stars
- When an iron core
forms, fusion stops
and gravity causes
the core to
collapse and the
star erupts in an
explosion called a
supernova
Neutron Stars and Black Holes
The collapsed core of a
supergiant may form an
extremely dense body called
a neutron star
Neutron stars emit little
visible light
Some neutron stars emit
beams of radio waves as they
spin – these stars are called
pulsars because the seem to
pulse as the beams rotate
Neutron Stars and Black Holes
Sometimes a supernova
leaves behind a core with
a mass more than three
times that of the Sun – it
collapses forming an
invisible object called a
black hole
The gravity of a black
hole is so strong that no
form of radiation can
escape from it
Stages in the Life Cycle of Stars
Star Systems
A binary star
system consists
of two stars that
orbit each other
A multiple star
system consists
of more than two
stars