Finding the stars
When observing the night sky, the first question that an astronomy fan is restless mind: What is a star? A star is a huge and bright sphere of hot gas, which produces its own energy through so-called nuclear reactions that take place in the core-center of the star making temperatures reach enormous values, and becoming the shining objects that are with us on our observations of the night sky on a clear night.
Stars have a life cycle like any living being, are born, grow to evolve and grow and eventually die and disappear, to safely trigger the birth of other new stars. But it happens so slowly that they cannot be seen in the timeline "human".
The Universe is an almost infinite space with room for millions of stars, star clusters and galaxies. The distance from the Sun, which is the nearest star, is called the Astronomical Unit, AU - and amounts to 149,597,870 km. Given that the speed of light is 300,000 miles per second, visible light observed from the Sun takes about eight minutes to reach earth. The next closest star to the Sun, is called Proxima Centauri, and light emitting takes longer than 4 years to reach Earth. This means that when you look at this star, is "seeing" how it was more than four years and you do not know how is at the present time. And indeed, when you observe the Sun with the proper eye protection, it "sees" what it was about eight minutes.
On clear nights, especially when viewed in the field with a small telescope, far from cities or towns that illuminate the night sky, you can also see areas nebulae where stars are born, such as Orion or M42 in the constellation of same name. These are called molecular clouds.
Molecular clouds are huge and deep dark clouds that are formed by a gas called hydrogen (99%) and solid-dust-matter in a very small proportion (1%), but enough so that under certain conditions, the stars can be born. You could say that these clouds provide the raw material for the main course which is the formation of stars.
The embryos of future stars are hidden inside of molecular clouds, and only the radio and infrared waves of the electromagnetic spectrum emitted by these embryos of stars, through these dark regions - the visible light does not-in So with appropriate equipment such as telescopes in space, we can interpret the results and develop a theory of star formation to reveal the secret.
The birth of a star
Although the proportion of dust in the cloud material is small compared with the amount of gas, these clouds are so extensive that they accumulate enough mass to generate thousands, even millions of stars like the Sun.
The training process is triggered when for some reason, a "fragmentation" of the cloud is broken into fragments, pieces of sufficient density-relationship between the amount of mass and volume occupied to begin to shrink slowly.
This process is irreversible, the fragment of cloud continues to contract and become more dense (less volume mass), to a value-twenty orders of magnitude greater than the original tag fragment - from which there is enough mass to begin to act the force of gravity, making the cloud collapses, it collapses under its own weight . Just form the core of the star: the protostar, which continues to fall on the rest of the field of fragment cloud.
As material continues to fall in the protostar, it begins to rotate, driving turn-like geysers, jets of matter at large distances and high speeds, making the protostar does not rotate too quickly, which would lead to its disintegration.
Because of this initial rotation, the subject of the tag is deposited preferentially in Ecuador of the protostar, forming what is known as a disk of matter orbiting the protostar, and that may be the seed of a future system of planets around it, similar to the solar system.
This first stage of star formation takes about 100,000 years, and as it is obscured by the dust cloud, is not only can be used, as mentioned before, radio telescopes (capture the emission of radio waves) or infrared telescopes to detect that stage. Then, as the material falls onto the protostar and the envelope dissipates, the embryo is visible. In a Sun-like star, this happens a million years after the start of the process of collapse.
After ten million years, the first-contraction process of collapse by gravity-end. During that time, the temperature of the protostar has grown enormously, and that temperature is so high that when the collapse ends, the calls begin to make thermonuclear reactions that use hydrogen as fuel is at the core of the star making it a heavier element called Helium. At this point we can say that a new star is born, and is in a phase of life called main sequence.
The star is stable as it is in a state known as hydrostatic equilibrium: the force that pushes outward-pressure energy-producing nuclear reactions is balanced by the force that pushes inward, gravity.