Human life is a very beautiful experience. The process starts with the fertilization of the egg, to the birth of a baby, through the life a person up until the death of that person. The life cycle of a star is a process that is just as beautiful and fascinating. Before the star begins its life, there are the components that will create the star. The components look as little like the star, then the sperm and the egg look like a baby. However, unlike the creation and life cycle of a human, the ultimate demise of a star is somewhat of a mystery. The most interesting aspects of life are during creation and during death, what happens during life, for that of a star at least, is quite inconsequential.
Before there was space, about 15 billion years ago, there was a set amount of matter. When the universe was formed it sprawled out an unfathomable amount of matter into every conceivable direction. The matter as it traveled created space as it traveled further from its origin. The matter hurled traveling at enormous speeds whipping around its self in trillions of spirals and collectively moving in a circular motion. On as many occasions as there are stars in the sky, groups of matter would spin together. Once this massive quantity of matter was spinning together, a star would be ready to be born.
The matter, in the form of gas, would spin around and around in an angular motion. Angular momentum is always conserved, in our world, and in space. If an ice skater is spinning around, they will bring their arms in closer in order to spin faster. As it relates to stars, the inverse is true, as the matter becomes smaller, that is closer together, it spins faster and faster. Eventually, the collection of gas develops its own gravity.
Now taking a step back, the gas that collects to make the star is very cold, about ten degrees Kelvin. It is in the gas form because it is so cold. Also it is in the gas form because at that point matter is not very dense, only about one thousand molecules per cubic centimeter. Once the matter experiences its own gravity, it condenses faster.
At this point some thermodynamic laws apply. Pressure and temperature are inversely related. That is, when you take X amount of matter and put it in Y amount of space, it will be Z degrees. However, when you take X amount of matter and put it into ?Y space, its temperature will be Z squared degrees. Likewise, as the star begins to condense more rapidly now because of the self-gravity, the same amount of matter is being put into as smaller volume, so the temperature raises. Eventually, the center of this spinning ball of matter becomes so hot, that it liquefies. Once the center liquefies, a "hydrostatic equilibrium" is reached. Hydrostatic equilibrium can best be explained by breaking it down into its word origin. "Hydro" - Pertaining to liquid; "static" means, "causing to stand" (Webster's, 420) and "equilibrium" means "a state of balance between opposing forces"(Webster's, 147). So basically the liquid at the center of the body is relatively stationary due to a balance of opposing forces. These two forces are the chemical reactions and explosions going on inside the center of the star and the gravitational force exerted inward cause by the size of the star.
That is the end of the birth of the star and the beginning of the life of the star. The star will continue burning the atomic fuel in its core to counter the gravitational force to endure its life until of course, the core of the star runs out of atomic fuel. Once the core of the star slows down the chemical reactions inside the star, the equilibrium is upset. And the star begins its death.
The death of the star is possibly the most interesting aspect of its entire life cycle.
The death of a star occurs in phases. Not all stars will visit each phase depending on the size of the star. The size of the star can be categorized in two ways: "stars with initial masses of less than about eight solar masses"(nasa.gov (1)) and "stars with initial masses greater than about eight solar masses"(nasa.gov (1)). The stars with initial masses of less than about eight solar masses, "small stars" will end by ejecting planetary nebulae. The planetary nebula is an expanding shell of gas ejected by a red giant late in its life. A red giant is what the star is called when it still is burning nuclear fuel on the surface of the star rather then the core. A small star exists as a red giant before it completely burns out of nuclear fuel and condenses to a density of "about a million to 10 million times that of water"(nasa.gov (2)) at which point the dead star is called a white dwarf. A star with an initial mass of greater than about eight solar masses, "large star", dies a completely and much more extravagant death. A large star dies by exploding, this explosion is called a supernova. A supernova is an awesome explosion that lasts for a very short time just before the star completely dies. When the supernova occurs, it releases as much light as an entire galaxy. After the supernova occurs, one of two things may happen. Either the star will become what is known as a neutron star, or it will become a black hole. The neutron star bares its name because it consists primarily of neutrons. The neutron star is significant because of its density. It weighs about 1.4 - 3 times as much as our sun, yet is only 12 miles in diameter. That makes it "100 to 1000 trillion times the density of water"(nasa.gov (2)).
The other alternative is for the supernova to become a black hole. A black hole is a phenomena not entirely explained in our universe. One theory is that a black hole is much like a cone, or a funnel, that leads to spot in the universe that has no volume but infinite mass, known as a singularity. This theory defies all of the laws of physics and relativity. But, black holes are very difficult to study. They are very difficult to observe because no light is emitted from them; also any light that comes near a black hole is sucked in because the gravitational force of the black hole is so great it pulls in even the basic element of light, the photon.
Supernovae are believed to be responsible for most of the matter that goes into the creation of new stars. Like a human being laid to rest, becoming part of the earth only to rise again, as food for another human's life. And so the life cycle continues.
Neufeldt, Victoria, Webster's New World Dictionary; Macmillian General Reference New York, NY; Ã‚Â©1995, 1989
Nasa.gov (2) http://observe.ivv.nasa.gov/nasa/space/stellardeath/stellardeath_6.html#PLANETARY_NEBULA