A star is a huge ball of gas and dust that gives out both heat and
light. When the gases in the star burn out, it dies. A star can live
for millions, even billions, of years depending on its size. Each
galaxy in the universe is made up of several billion stars.
Quick Q’s:
1. How many stars are
there in the universe?
We know of about 70
sextillion (7 followed
by 22 zeros) stars in
the universe. However,
we are only able to see
about 8,000 of these.
2. What are giant and
dwarf stars?
Scientists classify stars as
giant or dwarf stars on
the basis of their size.
The Sun is a dwarf star.
Supergiant stars – the
biggest in the universe
– are at least 400 times
bigger than the Sun.
3. What is a cluster
of stars?
Stars are usually
found in groups called
clusters. Some clusters
are made up of loosely
packed stars, while
other stars are packed
tightly together to
form a dense cluster.
4. What kind of stars
are binary stars?
Pairs of stars are
called binary stars.
Binary stars revolve
around the same
centre of gravity.
5. Which is the
brightest known star?
The Pistol Star is the
brightest known star in
the universe. It is about
10 million times
brighter than the Sun.
Q What is a protostar?
A Stars are born in clouds of dust and
gases, mainly hydrogen. More and more gas
is pulled together by gravity to form a cloud.
After a while the cloud begins to spin. This
makes the gas atoms bump into each other at
high speeds, creating a great deal of heat. As
the cloud becomes hotter a nuclear reaction
takes place inside, and the cloud begins to
glow. This glowing cloud is called a protostar.
The protostar continues to contract until it
becomes a star.
Q How long does a star live?
A A star glows for millions of years until the
gases in its outer layer begin to cool, and the
hydrogen in the inner core is slowly used up.
The cool outer layer starts to glow red. When
this happens the star is called a red giant. The
red giant continues to lose its brightness until
it fades away. Depending on its size, a red
giant may die in an explosion, get compressed
to form a black hole or become a white dwarf.
Q What is a white dwarf?
A A small star usually shrinks to form a
dense white dwarf. The size of a white dwarf
is similar to the size of Earth. There are many
white dwarfs in our galaxy but they are too
dim to be seen. Sirius B is one of them.
Q What is a supernova?
A A supernova is a vast explosion in
which an entire star is destroyed. After the
explosion, extremely bright light is emitted
for several days. Supernovas appear a billion
times brighter than the Sun. Sometimes, a
supernova explosion can go on for weeks
or even months. Supernovas mostly occur in
distant galaxies. The last supernova to take
place in the Milky Way occurred in 1604. It
was observed by the famous astronomer
Johannes Kepler. The brightest supernova to
be recorded so far is 1993J in the galaxy M81.
It was seen on 26 March 1993. But because
the stars are so far away, we may see a
supernova explosion long after it takes place.
Protostar
An artist’s impression of the original ball of dust and
gases that combine to form a protostar.
White dwarf
An enhanced image of white dwarf stars, which have
already shrunk to a size comparable to that of the
Earth. These stars are too dim to be detected without
modern telescopes.
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