The stars in the universe are classified in different types, from supergiants to dwarf stars.
The most numerous stars in the universe are the red dwarf, which represent the 80% of the total stars in our universe, and, like its name indicates, they are red, just as the most little of all. These stars, despite what the common sense says to us, these stars are the most cold and those that produce less energy in their insides. This can be explained because of their small size, which can be smaller than a half of the Sun, and they can produce a 0,001% to a 10% of the solar luminosity. Thanks to this, this stars are those that can live more time, they can last for tens of billions. The star of this type which is the nearest from the Earth is called Alpha Centauri, and it is at the same time the nearest star from the Earth apart from the Sun.
Another type of star is the yellow dwarf, this is the second type of stars less hot of all, and, like many other types of stars, they expand during the time. The yellow dwarfs are the second kind of stars that are more numerous in our universe. Its percentage represent a 10% of the total of the stars and they are relatively small too despite, that to our eyes, the Sun, which belongs to this type, seems gigantic.
Our star was formed about 4 600 millions of years ago, at the same time that the planets around him: Mercury, Venus, the Earth, Mars, Jupiter, Saturn, Uranus and Neptune. The nucleus of the Sun reaches a temperature of 15 millions ºC, and, while we get further from the nucleus, the temperature descends until we arrive to the surface, where the temperature is at 5 500 ºC. Further away, and even if it’s hard to believe, in the crown, that it extends to millions of kilometres from the star, and that comes to be the atmosphere of the Sun, the temperature arrives to the million of degrees Celsius!
Being a yellow dwarf, and due to the expansion process, the future of the Sun is to become a red giant, this giants can arrive until the Earth’s and Mars orbit, and, as I’ve said, this is the future that awaits the Sun in it’s last years of live, so, it will finish by burning Mercury, Venus and the Earth and arriving to their respective orbits.
Another type of stars are the called blue giants, this type is even bigger than the red giants, and, in this case we haven’t to trust the common sense neither, so these are the biggest of all, in fact, they can arrive to have an approximate volume of Jupiter’s orbit. These stars have a very short live, actually, they can only last for 10 to 100 million years, a very short live for a star. The future that awaits this stars are the red supergiants, these stars, are the biggest of them in terms of volume, in fact, they can be 200 times bigger than the Sun.
The end of the stars: White dwarfs and neutron stars
The future that awaits the stars is converting, for the most part of the time, into dwarf stars, which are white dwarfs and neutron stars. This is the case, for example, of the red dwarfs and the yellow dwarfs, which will finish they’re lives being white dwarfs. It is also the case of blue giants, this type of stars finish its days by converting into a neutron star or a black hole.
The white dwarfs are little stars that can’t produce energy for themselves any more, but that shine thanks to their high temperature. They’re very small, of about 10 000 km of diameter, but with an equivalent mass to the Sun’s. Stars that end in this form are the red dwarfs and yellow dwarfs.
The neutron stars are the remainders of a red supergiant. With 20 km of diameter, they have a total mass of 1,5 suns, but, despite of they’re small size, they are so dense that, a little spoon of coffee taken in those stars, would weigh one hundred tones in the Earth!