2 What are Stars?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.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.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
3 What are Stars made of?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.
4 Life cycle of a Star Nebula Gravity clumps gas and dust together Pressure increases= nuclear fusionStar is bornStar is spinning and other gases clump onto itA few million years later star’s birth process is completeAverage star lives about 10.5 billion yearsDying 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 carbonMeanwhile heavy elements were building up in the star’s coreStar can’t run on carbonSo it explodes (supernova)Or shed all it’s gases into an planetary nebulaThat causes core shrinking effectSometimes element build up in the star’s core is too muchSo when it shrinks it becomes a black hole
6 Types of stars Stars come in many different varieties Red dwarf Yellow starsBlue giantsRed giantsSuper red giantsEtc.
7 Red DwarfRed dwarf stars are by far the most common type of star in outer spaceRed 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 fuelWhy 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.
8 Yellow starLike the Sun, these medium sized stars are yellow because they have a medium temperatureTheir higher temperature causes them to burn their fuel faster this means they will not live as long, only about 10 billion years or soNear the end of their lives, these medium sized stars swell up becoming very largeWhen 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
9 Blue giantsBecause blue stars are large and compact, they burn their fuel quickly, which gives them a very high temperatureThese stars often run out of fuel in only 10, ,000 years a blue giant is very brightLike 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 nightBlue giant stars die in a spectacular wayThey 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
10 Red giants 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 togetherAs 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 heliumOnce ignited, helium burns much hotter then hydrogenThe additional heat pushes the outside of the star much further than it used to be, making the star much larger
11 Super Red giantsA super giant star is the exact same thing as a giant star, only biggerRemember 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 outJust like the sun sized stars blue giant stars also begin to burn helium. As they do these stars get much hotterThis 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 hotterThe 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.
12 Bibliography Wiki answers Ask an astronomer.com Google images Nasa Kid astronomy.comAsk the van.comThe big book of stars and planets by Robin Kerrod