Introduction
Stars are alive. They are born, they live, and then they die. Even the sun is not immortal, as many once believed. In five billion years it will die, and its remains will be recycled into a new star. There is an incredible amount of power in a star. When some stars die, this power is released in an awesome explosion that is so powerful it can create entire solar systems.
Star birth
All stars are born in giant gas nurseries called molecular clouds. These vast clouds contain dust, hydrogen and helium. Although the gas inside a molecular cloud is much, much thinner than the atmosphere on Earth, there is just enough gravity to force the cloud to contract. Parts of cloud will shrink and heat up until nuclear fusion reactions start in its core and it becomes a star. Stars spend most of their lives in a stable state of nuclear fusion called the main sequence. Stars like our sun can spend billions of years in this state, gradually using up all their hydrogen as it is converted into helium.
Star sizes
When you look up at the stars, they all seem to be very similar in sizes. However, stars actually come in an enormous range of sizes, from hunderds of times larger than our sun to smaller than our Earth. Red supergiants are the largest stars. They can grow to over 500 times the size of our sun. The most common stars in the galaxy are those of the same size as sun. When these stars die, they become white dwarfs and shrink to the size of Earth. They are even smaller stars than this. Neutrons stars are so compact that they can be less than a few kilometres in diameter.
Supernovae
Large stars, with a mass much greater then our sun, die a dramatic death. As the hydrogen in a large star is used up, it begins to expand, becoming red supergiant. When it runs out of energy, the core of a red supergiant turns to iron and collapses under its own immense gravity. The speed of this collapse creates a giant explosion as the star sheds out its outer layers. This tremendous explosion, called a supernova, can be brighter than a billion suns and is powerful enough to create new stars. Only a tiny, dense remainder is left, either a neutron star or a black hole.
(click here to get the image)
Some important facts
1) Most stars are not born on their own, but in groups. The Pleiades star cluster is a group of similar aged stars that are still surrounded by the cloud of dust from which they formed.
2) A star begins to form when an enormous cloud of gas and dust begins to contract under its own gravity.
3) As it shrinks, the cloud becomes much denser and hotter,the centre glowing red.
4) When the temperature in the cloud's core is 10 million nuclear reactions will start, and the ball of gas becomes a star.
5) The star spend most of its life in its main sequence, turning hydrogen into helium and remaining unchanged for millions of years.
6) As the hydrogen in the star's core runs out, the star expands to become a red giant, or even a red supergiant.
7) Smaller stars will quickly run out of fuel as red giants. They will cast off their useless outer layers to form an expanding cloud called a planetary nebula.
8) Eventually, the planetary nebula will disperse, leaving the star's core, a tiny, dense ball called a white dwarf. This will gradually cool and die.
Facts and figures
Nearest stars : distance :
Proxima Centauri 4.2 light years
Alpha Centauri 4.3 light years
Barnard's Star 6 light years
Wolf 359 7.7 light years
Lalande 21185 8.2 light years
Sirius A 8.6 light years
Sirius B 8.6 light years
UV Ceti A 8.9 light years
Ross 154 9.6 light years
Stars are alive. They are born, they live, and then they die. Even the sun is not immortal, as many once believed. In five billion years it will die, and its remains will be recycled into a new star. There is an incredible amount of power in a star. When some stars die, this power is released in an awesome explosion that is so powerful it can create entire solar systems.
Star birth
All stars are born in giant gas nurseries called molecular clouds. These vast clouds contain dust, hydrogen and helium. Although the gas inside a molecular cloud is much, much thinner than the atmosphere on Earth, there is just enough gravity to force the cloud to contract. Parts of cloud will shrink and heat up until nuclear fusion reactions start in its core and it becomes a star. Stars spend most of their lives in a stable state of nuclear fusion called the main sequence. Stars like our sun can spend billions of years in this state, gradually using up all their hydrogen as it is converted into helium.
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| STARS |
When you look up at the stars, they all seem to be very similar in sizes. However, stars actually come in an enormous range of sizes, from hunderds of times larger than our sun to smaller than our Earth. Red supergiants are the largest stars. They can grow to over 500 times the size of our sun. The most common stars in the galaxy are those of the same size as sun. When these stars die, they become white dwarfs and shrink to the size of Earth. They are even smaller stars than this. Neutrons stars are so compact that they can be less than a few kilometres in diameter.
Supernovae
Large stars, with a mass much greater then our sun, die a dramatic death. As the hydrogen in a large star is used up, it begins to expand, becoming red supergiant. When it runs out of energy, the core of a red supergiant turns to iron and collapses under its own immense gravity. The speed of this collapse creates a giant explosion as the star sheds out its outer layers. This tremendous explosion, called a supernova, can be brighter than a billion suns and is powerful enough to create new stars. Only a tiny, dense remainder is left, either a neutron star or a black hole.
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| SUPERNOVA |
Some important facts
1) Most stars are not born on their own, but in groups. The Pleiades star cluster is a group of similar aged stars that are still surrounded by the cloud of dust from which they formed.
2) A star begins to form when an enormous cloud of gas and dust begins to contract under its own gravity.
3) As it shrinks, the cloud becomes much denser and hotter,the centre glowing red.
4) When the temperature in the cloud's core is 10 million nuclear reactions will start, and the ball of gas becomes a star.
5) The star spend most of its life in its main sequence, turning hydrogen into helium and remaining unchanged for millions of years.
6) As the hydrogen in the star's core runs out, the star expands to become a red giant, or even a red supergiant.
7) Smaller stars will quickly run out of fuel as red giants. They will cast off their useless outer layers to form an expanding cloud called a planetary nebula.
8) Eventually, the planetary nebula will disperse, leaving the star's core, a tiny, dense ball called a white dwarf. This will gradually cool and die.
Facts and figures
Nearest stars : distance :
Proxima Centauri 4.2 light years
Alpha Centauri 4.3 light years
Barnard's Star 6 light years
Wolf 359 7.7 light years
Lalande 21185 8.2 light years
Sirius A 8.6 light years
Sirius B 8.6 light years
UV Ceti A 8.9 light years
Ross 154 9.6 light years
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