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The stars are huge celestial spherical bodies, which exists in very big number in the universe. They are made by gas and vary a lot in brightness, volume, density, mass and sizes.
Some stars stay alone, some of them have partners (binary stars) and others make part of groups, the constellations.
The stars are luminous bodies and they produce energy by the nuclear fusion - they turn Hydrogen gas molecules into Helium gas molecules (after we will tell you how and why!). To be stars and to be able to have enough pressure for the fusions to happen, the stars have to have a minimum mass (more or less 81 times the Jupiter mass). Otherwise, the bodies will not be stars, but red dwarfs. These fusions led to several elements, such as the iron, the nickel and other metals.
A lot of stars that we see from here already died, but the distance to those stars is so big that the light emitted by them takes too long to get here, so many times then that light get here, the star itself is already gone.
Its birth and evolution
Stars came out of the concentration of gas and cosmic dust by
gravitational sources spread over the universe. The gas begins to concentrate more and more and become warmer. The inside of the cloud is so hot that the star begins to produce a lot of light.
The birth of the star can last for millions of years. The star maintains alive with the energy produced by the fusion of Hydrogen gas into Helium gas – the Hydrogen is used like fuel for the stars - and as the Hydrogen is used the star change its size and color. This time of its life is called the Main Sequence.
OBS: The energy produced is the bright we see from Earth.
Types of Stars
Dwarf stars. There are dwarf stars whose main characteristic is that the process of energy production is the fusion of protons (hydrogen nuclei). Our Sun is a dwarf star.
Star of Preons. Made of subatomic particles. Stars of preons have extremely high densities, intermediate between the neutron stars and black holes. It is defined as one that belongs to a class of stars that are bright as the stars of the main sequence.
Giant star is a star with radius and luminosity much higher than those of a star's main sequence. Typically, giant stars have radii between 10 and 100 solar radii and luminosity between 10 and 1,000 times then the sun warm and bright. A star's main sequence can also be cited as giant.
Supergiants stars are among the most massive stars. The most luminous of supergiants are often classified as hypergiants of class 0. Vary greatly in distance, usually between 30 and 500, or even more than 1000 solar radii. Because of its excessive mass, they have a short (in stellar terms) life cycle of only 10 to 50 million years.
Star hypernova is a type of supernova produced when exceptionally large stars collapse at the end of its life cycle.
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