The evolution of stars

Discovering the stars

When observing the night sky, the first question that a young woman becomes restless mind is: What is a star? A star is a huge sphere of hot gas and bright, which produces its own energy through so-called nuclear reactions taking place in the core-center of the star, causing enormous temperatures reach and becoming the shining objects that accompany us on our observations of the night sky on clear nights.

Stars have a life cycle like any living being are born, develop evolving and growing and eventually die and disappear, to safely trigger the birth of other stars. But this happens so slowly that they can be seen in the time scale of "human".

The Universe is an almost infinite space with room for millions of stars, star clusters and galaxies. The distance to the Sun, which is the nearest star, is called the Astronomical Unit, AU - and amounts to 149,597,870 km. Given the speed of light is 300,000 miles per second, visible light is observed from the Sun takes about eight minutes to reach earth. The next nearest star to our Sun, is called Proxima Centauri, and the emitted light takes more 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 not know how at the present time. And indeed, when looking at the Sun with adequate protection in the eye "sees" what it was about eight minutes.

Molecular clouds

On clear nights, especially when viewed in the field with a small telescope, far from cities or towns to illuminate the night sky, you can also see areas where stars are born nebulae such as Orion or M42 in the constellation of same name. They are called molecular clouds.

Molecular clouds are enormous cold, dark clouds that are formed by a gas called hydrogen (99%) and dust-solid matter in a very small proportion (1%), but enough so that under certain conditions, can be born stars. It can be said that these clouds are the raw material for the main course which is the formation of stars.

The embryos of future stars are hidden inside the molecular clouds, and only the radio waves and infrared electromagnetic spectrum emitted by these embryos of stars go through these dark areas - 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 accumulate enough mass to generate thousands, even millions of stars like the Sun

The training process is triggered when there is somehow a "fragmentation" of the cloud, which is broken into fragments, pieces of sufficient density-relation between the amount of mass and volume occupied to begin to shrink slowly.

This process is irreversible, the fragment cloud continues to contract and become more dense (less volume mass), reaching a value-twenty orders of magnitude larger than the original cloud fragment - from which there is enough mass to begin to act the force of gravity, causing the cloud to collapse, sink, under its own weight. They just formed the core of the star: the protostar, which continues to fall on the other stuff in the cloud fragment.

As material continues to fall in the protostar, it begins to rotate, driving turn-like geysers, jets of matter at large distances and at high speed, causing the protostar does not turn too quickly, leading to its disintegration.

Because of this initial rotation, the cloud material is deposited preferentially in Ecuador of the protostar, forming what is known as a disk of matter orbiting the protostar, which 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 dust in the cloud, is not only can be used, as mentioned earlier, radio telescopes (the emission capture radio waves) or infrared telescopes to detect this stage.

Then, as the material falls onto the protostar and envelope dissipates, the embryo becomes visible. In a star like the Sun, this is a million years after the start of the process of collapse.

After ten million years, the first process of collapse-contraction by gravity-ends. During that time, the temperature of the protostar has grown enormously, and this temperature is so high that when the collapse ends begin to occur called 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 that 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 compensated by the force that pushes inward, gravity .