As far back as the beginning man, people have looked to the heavens and wondered what is actually up there.  Many have hypothesized, studied, and used various sorts of equipment to research the heavens.  However, one topic has been able to catch the attention of the people more than any other, black holes.  To some, black holes are that of science fiction, sucking up everything in space.  However, scientific merit does lie within the hypothetical existence of these objects in space.  To understand one though, one must first examine where they come from, stars.

A star is basically a spherical ball of hot gas, however there is a great deal of physics going on inside one.  The outer layers of a star are partially ionized and the inner layers are fully ionized.  The full ionization is due to the fact that the temperature and pressure are much higher than on the outer layers.  Sense the inner layers are fully ionized, the gas is made up of free electrons and bare atomic nuclei.  The core generates continuous radiation where photons of light are emitted.  The photons of light slowly make their way to the surface.  The outer layer from which they leave the star to enter space is called the photosphere.   Once gas begins flowing from the star, light from the star can exert sufficient force to accelerate the gas to high speeds.  Thus, the term stellar winds in coined, which is also known as radiation pressure.  This radiation pressure works in an outward direction works against gravity working in an inward direction.  This struggle between the forces, called hydrostatic equilibrium, is how a star stays in a constant spherical shape.  The lifetimes of star is dependent on how quickly it can produce energy and how fast it can radiate that energy into space.  For example, a very massive star may have a much larger amount of energy, however it also radiates that energy at a much higher rate than a small star, thus the smaller star will typically have a shorter life expectancy.  As the star goes through its life cycle, it may go through several changes in its chemical make up.  When a star uses up a source of nuclear fuel another may ignite if the temperature in the core is high enough.  Thus, only massive stars with a high internal temperature typically go through a lot of nuclear fuels.  The stars that go through a lot of elements will start of with hydrogen then go through the following other sources:  helium, carbon, oxygen, neon, silicon, and iron.  Hence, a star that goes through the cycle will undergo an enrichment of heavy elements.

          A star may go through many changes in its lifetime, however it has to first be formed. The gravitational collapse of an interstellar cloud is how a star the size of our sun of one solar mass begins to form.  It is uncertain what force acts upon the cloud to cause it to collapse upon itself initially. However, once the collapse has begun gravity will take over and begin to pull it all together.  The collapse occurs much more rapid at the center of the cloud; thus the density increases here at a higher rate than the outer portions.  Interestingly enough, the core of the cloud remains relatively cool due to the fact that the heat produced escapes in the form of infrared radiation.   However, when the density of the core is high enough the cloud will to trap the infrared radiation, thus causing the temperature to increase and slowing the central contraction down.  As the outer portions continue their infall towards the center, heat and shockwaves are produced.  The adding heat forces the hydrogen molecules in the core to break up.  The break up absorbs the heat from the gas thus reducing the pressure.  The reduced pressure causes a second collapse to occur.  The pressure again rises after the second collapse in order to counterbalance gravity.  The central portion again beings to contract upon itself.  As heat builds up due to the contraction the core will become hot enough to start nuclear reactions.  The energy being pushed out fully counterbalances gravity and the contraction processes cease; this process is refereed to as hydrostatic equilibrium.