Red Giant, White Dwarf, Our Sun, and Black Holes

After a few billion years the center of a star runs out of nuclei of hydrogen atoms (Protons). What is left is a core made of nuclei of helium atoms (Alphas). The outer layers of the star still contain hydrogen, but they are not hot enough to fuse. Because it has run out of fuel, the star begins to cool, and contract. The outer layers of the star fall inwards under gravity, and as they fall they heat up. A shell surrounding the central core becomes hot enough to fuse protons into alphas. So the star gains a new source of energy. The core of the star is now hotter than it was during its normal life and this heat causes the outer parts of the star to swell. The star becomes a giant. The radiation from the fusing shell has grown weak by the time it reaches the surface of the star. Weak radiation is red, so the star becomes a red giant.

White Dwarfs are the remnants of stars that were massive enough to stay alive using nuclear fusion in their cores, but not massive enough to blow apart in a Type II supernova. When stars like our own sun die they will become white dwarfs. As a star like our sun is running out of fuel in its core it begins to bloat into a red giant. A typical white dwarf is about the size of the Earth. It is also very dense and hot. A spoonful of white dwarf material on Earth would weigh as much as a car.

The Sun appears to have been active for 4.6 billion years and has enough fuel to go on for another five billion years or so. At the end of its life, the Sun will start to fuse helium into heavier elements and begin to swell up, ultimately growing so large that it will swallow the Earth. After a billion years as a red giant, it will suddenly collapse into a white dwarf. The final end product of a star like ours. It may take a trillion years to cool off completely.

A black hole is a region of spacetime from which nothing can escape, even light.
To see why this happens, imagine throwing a tennis ball into the air. The harder you throw the tennis ball, the faster it is travelling when it leaves your hand and the higher the ball will go before turning back. If you throw it hard enough it will never return, the gravitational attraction will not be able to pull it back down. The velocity the ball must have to escape is known as the escape velocity and for the earth is about 7 miles a second. As a body is crushed into a smaller and smaller volume, the gravitational attraction increases, and hence the escape velocity gets bigger. Things have to be thrown harder and harder to escape. Eventually a point is reached when even light, which travels at 186 thousand miles a second, is not travelling fast enough to escape. At this point, nothing can get out as nothing can travel faster than light. This is a black hole.

All Stars will start out as a protostar which is like the fetus of all stars and where a baby begins it's life. After a protostar with fusion ignition it will ignite into a main sequence star which for a human is like infancy through adulthood. Through years and years the main sequence star will explode into a red giant or a super giant (Like the sun) which can relate to the middle age years of adulthood. when the star matures out of a red giant it becomes a white dwarf which would be the grandma or grandpa of the human life cycle. And of course like everything it's life will have to end and eventually it will die causing the star to become a black hole, thus ending the stars life, which would be death for a human.

As you can tell there is a long journey for a star. Going through some intersting phases. My favorite phase would have to be the black hole. Just for the simple fact that there are a lot of people and scienctists out there thay don't believe black holes exist.