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Astronomy for Beginners
Stars
By Aashman Vyas
What are Stars?
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Stars are gigantic balls of gas, mostly hydrogen gas. There is so much gas
and other material that the gravity of this huge gas-ball holds everything
together. There is so much gravity that the gas becomes very dense and
hot.
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Our own sun is a star. Fortunately, we are far enough away from it that the
gravity of the gas can’t pull us in. It would be rather unpleasant inside of a
star.
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The gravity is strong enough that it squeezes the gas together so tight that
nuclear fusion occurs. That means that the nuclei (centers) of the atoms get
stuck together and ’fuse’. This releases a lot of energy and causes the stars
to heat up. The heat works its way from the inside of the star to the surface,
and then radiates into space. So what we see of stars is the energy
released from the nuclear reactions inside their cores and then radiated
from the surface. There are many different kinds of stars. They come in
many sizes and colors.
Some stars even orbit around each other. We call these binary stars
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What are Stars made of?
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Stars are made of very hot gas. This gas is mostly
hydrogen and helium, which are the two lightest
elements.
Stars shine by burning hydrogen into helium in their
cores, and later in their lives create heavier
elements. Most stars have small amounts of heavier
elements like carbon, nitrogen, oxygen and iron,
which were created by stars that existed before
them.
After a star runs out of fuel, it ejects much of its
material back into space. New stars are formed from
this material. So the material in stars is recycled.
Life cycle of a Star
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Nebula
Gravity clumps gas and dust together
Pressure increases= nuclear fusion
Star is born
Star is spinning and other gases clump onto it
A few million years later star’s birth process is complete
Average star lives about 10.5 billion years
Dying process:
Star burns up fusion fuel (hydrogen) and turns to helium.
To adapt to helium star grows bigger (red giant)
Few billion years later, star consumes helium and turns it to carbon
Meanwhile heavy elements were building up in the star’s core
Star can’t run on carbon
So it explodes (supernova)
Or shed all it’s gases into an planetary nebula
That causes core shrinking effect
Sometimes element build up in the star’s core is too much
So when it shrinks it becomes a black hole
Life cycle of a star 2
Types of stars
Stars come in many different varieties
 Red dwarf
 Yellow stars
 Blue giants
 Red giants
 Super red giants
 Etc.
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Red Dwarf
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Red dwarf stars are by far the most common type of star in outer
space
Red Dwarf stars can range in size from a hundred times smaller
than the sun, to only a couple of times smaller. Because of their
small size these stars burn their fuel very slowly, which allows them
to live a very long time. Some red dwarf stars will live trillions of
years before they run out of fuel
Why are red dwarf stars red?
Because red dwarf stars only burn a little bit of fuel at a time, they
are not very hot compared to other stars. Think of a fire. The coolest
part of the fire at the top of the flame glows red, the hotter part in the
middle glows yellow, and the hottest part near the fuel glows blue.
Stars work the same way. Their temperature determine what color
they will be.
Thus we can determine how hot a star is just by looking at its color.
Yellow star
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Like the Sun, these medium sized stars are yellow
because they have a medium temperature
Their higher temperature causes them to burn their fuel
faster this means they will not live as long, only about 10
billion years or so
Near the end of their lives, these medium sized stars
swell up becoming very large
When this happens to the Sun it will grow to engulf even
the Earth. Eventually it will shrink again, leaving behind
most of their gas. This gas forms a beautiful cloud
around the star called a Planetary Nebula
Blue giants
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Because blue stars are large and compact, they burn
their fuel quickly, which gives them a very high
temperature
These stars often run out of fuel in only 10,000 - 100,000
years a blue giant is very bright
Like a light house, they shine across a great distance.
Even though blue giant stars are rare, they make up
many of the stars we see at night
Blue giant stars die in a spectacular way
They grow larger just like the Sun sized stars, but then
instead of shrinking and forming a planetary nebula they
explode in what is called a super nova. Super nova
explosions can be brighter than an entire galaxy, and
can be seen from very far away
Red giants
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Remember when I talked about sun sized stars?
I said that at the end of their lives these stars expand, taking up
much more space then before. This is exactly what a Red Giant Star
is.
As a sun sized star gets old, it starts to run out of its hydrogen fuel.
When the burning of hydrogen in the star's core begins to slow
down, the core gets more compact. This means all the stuff in the
middle of the star gets really close together
As the center gets smaller and smaller it starts to heat up again.
When it gets hot enough it will start to burn a new fuel called helium
Once ignited, helium burns much hotter then hydrogen
The additional heat pushes the outside of the star much further than
it used to be, making the star much larger
Super Red giants
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A super giant star is the exact same thing as a giant star,
only bigger
Remember that as a star gets older it begins to run out
of fuel. As the star runs out of fuel, it will start to burn out
Just like the sun sized stars blue giant stars also begin to
burn helium. As they do these stars get much hotter
This extra heat makes the outside of an old blue giant
star stretch out further. Remember how hot air balloons
stretch out as the air in them gets hotter
The only difference between Giant Stars and Super
Giant Stars is their size. Super Giant Stars are much
bigger. If the Sun were replaced by a super giant star it
would extend almost all the way out to Uranus.
Bibliography
Wiki answers
 Ask an astronomer.com
 Google images
 Nasa
 Kid astronomy.com
 Ask the van.com
 The big book of stars and planets by
Robin Kerrod
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Thank You For Watching!!!