Preview referat: Black holes
This energy produced is so great when it first collides, that a nuclear reaction occurs and the gases within the star start to burn continuously. The Hydrogen gas is usually the first type of gas consumed in a star and then other gas elements such as Carbon, Oxygen, and Helium are consumed. This chain reaction fuels the star for millions or billions of years depending upon the amount of gases there are. The star manages to avoid collapsing at this point because of the equilibrium achieved by itself.
The gravitational pull from the core of the star is equal to the gravitational pull of the gases forming a type of orbit, however when this equality is broken the star can go into several different stages. Usually if the star is small in mass, most of the gases will be consumed while some of it escapes. This occurs because there is not a tremendous gravitational pull upon those gases and therefore the star weakens and becomes smaller. It is then referred to as a White Dwarf. If the star was to have a larger mass however, then it may possibly Supernova, meaning that the nuclear fusion within the star simply goes out of control causing the star to explode.
After exploding a fraction of the star is usually left (if it has not turned into pure gas) and that fraction of the star is known as a neutron star. A black hole is one of the last option that a star may take. If the core of the star is so massive (approximately 6-8 solar masses; one solar mass being equal to the sun's mass) then it is most likely that when the star's gases are almost consumed those gases will collapse inward, forced into the core by the gravitational force laid upon them. After a black hole is created, the gravitational force continues to pull in space debris and other type of matters to help add to the mass of the core, making the hole stronger and more powerful.
Most black holes tend to be in a consistent spinning motion. This motion absorbs various matter and spins it within the ring (known as the Event Horizon) that is formed around the black hole. The matter keeps within the Event Horizon until it has spun into the centre where it is concentrated within the core adding to the mass. Such spinning black holes are known as Kerr Black Holes. Most black holes orbit around stars due to the fact that they once were a star, and this may cause some problems for the neighboring stars. If a black hole gets powerful enough it may actually pull a star into it and disrupt the orbit of many other stars. « mai multe referate din Astronomie