1. Life Cycle of a Star

2. Interactive Support Sites
Meta Café (3 minute video)
Life Cycle of a Star

3. Nebula Stars are born from clouds of dust and gas in space.
These clouds, called nebula, coalesce as a result of the gravitational pull of the particles themselves as well as nova shock waves, passing stars or galaxies.
Elements such as helium and hydrogen, dust and other elements begin to clump together and create a communal gravity into which more and more particles are drawn.

4. Protostar The newly formed protostar continues to grow.
When the protostar contracts, it begins to develop its own "wind".
As the star material takes shape, not all the dust and gas is blown away.
It remains trapped in the protostars gravity and forms a disk.
Matter within the disk can clump together to form planets if there is sufficient material left in the disk.

5. Protostar Protostars are stars that have not lit up yet.
They sit at the center of a cloud of dust and gas collecting enough stuff to start a nuclear reaction.
The smallest mass possible for a star is about eight percent that of our own Sun.
Anything smaller will not allow a nuclear fusion reaction to take place.
Smaller than this critical mass are the so-called brown dwarfs that may shine dimly for a while or simply become a gas planet like Jupiter.

6. Middle Age Star
At some point nuclear fusion begins at the core of the star where hydrogen is turned into helium causing a release of vast amounts of energy.
This energy presses outward against the inward gravitational pressure of the gas which makes up the star body.
The process is called the “main sequence” and can last billions of years.
What results is referred to as a Middle Age Star.

7. Red & Yellow Dwarf Stars
Red and yellow dwarf stars are main sequence stars.
Red dwarfs are small and burn very slowly over incredibly long periods of time.
Yellow dwarfs are more stable and probably are the only kinds of stars that have any chance to harbor life on their planets. Our Sun is a yellow dwarf star.

8. Life Span
Throughout the main sequence, the star very slowly contracts to compensate for the loss of energy (heat and light).
With contraction, the core becomes more dense and the pressure at the core rises.
At the same time, the temperature of the core rises because of the gravitational crush of the denser makeup of the contracting star.

9. Life Span
The size and strength of the star will be controlled throughout the life span of the star by the balance between gravity pushing in and gas pressure pushing out.
Throughout the star's lifespan, nuclear fusion converts hydrogen to helium and maintains equilibrium.
The larger the star to begin with, the more fuel it has to burn to maintain that equilibrium.

10. Life Span
This means nuclear fusion occurs at a faster rate in bigger stars.
This causes big stars to use up their fuel faster and shortens the stars life span. (Approximately 4-5 billion years.)
A smaller star burns fuel at a slower rate, so it lives longer. (Approximately 10 billion years.)

11. Red Giant or Red Super Giant
Once a star begins to use up the hydrogen at its core, the core collapses creating more heat.
If it gets hot enough, nuclear fusion ignites the hydrogen in the outer shell. This creates increased outward gas pressure and causes the shell to expand rapidly and cool.
The star then becomes a red giant. The core, however, under the crush of gravity continues to collapse until nuclear fusion ignites even the helium and turns it into carbon and oxygen.

12. Red Giant or Red Super Giant
Red giants are a part of the normal life cycle of a star that has enough mass to ignite the hydrogen in the outer shell toward the end of the main sequence period.
Really huge stars are referred to as Red Super Giants and go on until their cores are converted to solid iron.
Red super giants may shine more than a million times as brightly as the Earth's sun.

13. Old Age: Low Mass Star
A low mass star may survive for billions of years (10 billion years), but the hydrogen and helium gets used up before it gets hot enough to fuse carbon.
When that happens, the star blows away its outer layers and creates what is called a planetary nebulae, which provides material for more protostars.
At the center of the planetary nebulae is a white dwarf which is about the size of Earth.

14. White Dwarf
White dwarfs are what is left after a red giant blows away its outer layers and shrinks. They are small and represent the normal last stage of a star's life.
They have the same mass as Earth's sun, but only one percent or less of its diameter.
White dwarfs are very dense and cool and fade for several billion years.

15. Old Age: High-Mass Star
A high-mass star does not live as long (4-5 billion years), but quickly develops an iron core and explodes as a nova or a supernova.
What remains is referred to as a supernova remnant.
The remaining core can then become either a very dense neutron star for a less massive star) or the impossibly dense black hole (for a more massive star.

16. Neutron Star
Neutron stars are massively dense stars that are not quite dense enough to become black holes.
If neutron stars spin very fast, scientists believe they become pulsars.

17. Black Hole
Black holes are the remains of massive stars that have become so dense that nothing can escape their gravity, not even light or stars.
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