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The BIRTH of a Star
A star is born when gas and dust particles come together and make a
cloud, called a Nebula. Gravity starts to compress the cloud, forcing
the atoms to move closer. This starts a process called fusion. Fusion
occurs when the atoms are so close together that they start to
combine, making helium from hydrogen. When this happens, energy
is created and a new star is formed!
The LIFE of a Star
The length of a star’s life is determined by its mass. A star with a small mass
will live longer than a star with a large mass because it burns less gas. The
temperature of a star determines its color. The hottest stars are blue or white
and the coolest stars are red or yellow.
As a star goes through its life, it continues to fuse hydrogen molecules into
helium molecules for fuel. As these molecules run out the star grows dimmer.
The DEATH of a Star
A star dies when it runs out of hydrogen molecules which it uses
for fuel. When this happens, the star can no longer hold up its
mass, and it begins to collapse. Depending on the mass of the
star, it dies a different death. Larger stars die violently, with a
giant explosion. After the explosion, a small portion of the star
is left behind to begin again. Smaller stars die peacefully and
turn into Brown Dwarfs.
BINARY Stars
Binary stars are a group of two or
three stars that orbit around each
other at a close distance. The group
of stars rotate around a common
center of mass. An example of this
is the north star, Polaris.
WHITE DWARF
White Dwarfs
are formed
when smaller
stars die.
They are the
hottest of all
dwarf stars.
We know this
because of
their white
color. When
our sun dies in
about a billion
years, it will
become a
white dwarf.
BLACK DWARF
A black dwarf is a star that has completely run out of hydrogen molecules.
Black dwarfs do not exist in our galaxy yet, because it is not old enough.
Computer simulations have told us that they will exist billions of years from
now.
RED GIANT
Red giants are large, and relatively cool, stars. They occur after a mediumlarge star collapses. After a star (like our sun) dies, it temporarily swells in size
and then cools, before becoming a white dwarf.
SUPERGIANT
Supergiants are the largest and brightest stars in the galaxy.
Red supergiants are larger than blue ones, but less hot. When
a large star runs out of hydrogen to fuse, it expands to
become a red giant. When it reaches the stage of burning
helium to carbon, it expands and become a red supergiant.
Through strong winds, red supergiants are changed into a
smaller and hotter blue supergiants.
SUPERNOVA
The explosion called a supernova occurs after a large star has become a red
supergiant. When the star stops expanding because it can no longer create
enough energy to support its own mass, it collapses completely and makes a
giant explosion. A supernova is brighter than all the stars in the galaxy
combined! The energy created by the explosion can travel at a speed of a
thousand miles per second. Supernovas also help to create other stars.
NEUTRON Star
Neutron stars are created in
the last phase of a mediumlarge star’s death. They are
mostly made up of the center
of atoms and are very dense.
Neutron stars do not become
a black hole because they do
not have enough mass.
BLACK HOLES
After a supernova
explosion, a black
hole is created.
The remains of the
star creates an
object so dense
that the force of
gravity traps
everything that
comes near them.
Even light cannot
escape the black
hole’s gravity. This
is why it is black.