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For a long time it was thought that the milky Way was formed gradually. In 1962, Olin Eggen, Donald Lynden-bell and Allan Sender proposed a hypothesis which became known as the ELS model (it was named from the initial letters of their names). According to her, in the place of the milky Way once slowly rotating homogeneous cloud of gas. It was like a ball and reached across about 300 thousand light years, and consisted mainly of hydrogen and helium. Gravity protogalactic shrank and became flat; however, its rotation is accelerated markedly.
For almost two decades, this model satisfied the scientists. However, the new observations showed that the milky Way could not occur as he has prescribed theorists.
According to this model, initially formed a halo, and then the galactic disk. However, the disk also are very ancient stars, for example, the red giant Arcturus, whose age is over ten billion years, or the many white dwarfs of the same age.
And in the galactic disk and in the halo of the detected globular clusters that are younger than the ELS model. Obviously, they are absorbed by our Galaxy at a later date.
Many stars in the halo rotate in a different direction than the milky Way. Perhaps they too were once outside the Galaxy, but then was involved in this "star swirl" — like a random swimmer into a whirlpool.
In 1978, Leonard Searle and Robert Zinn proposed a model of formation of the milky Way. It was designated as a "model of SZ". Now the history of the Galaxy became noticeably more complicated. More recently, her youth, in the view of the astronomers described, just as, in the opinion of physicists rectilinear translational motion. Mechanics of what is happening was clearly visible: there was a uniform cloud; it consisted only of evenly spilled gas. Nothing his presence did not complicate the calculations of theorists.
Now instead of one huge cloud in the visions of scientists came several small, quaint scattered clouds. Among them was visible and the stars; however, they were located only in the halo. Inside halo still seething clouds encountered; the gas mass is mixed and compacted. Over time, this mixture formed the galactic disk. It began to emerge a new star. However, this model was later criticized.
It was impossible to understand what tied the halo and galactic disk. This condensing disk and sparse star shell around him had little in common. After Searle and Zinn have compiled a model, it was found that the halo is rotating too slowly, so that it formed the galactic disk. Judging by the distribution of chemical elements, the latter arose from protogalactical gas. Finally, the angular momentum of the disk was ten times higher than halo.
The secret is that both models contain a grain of truth. The trouble is that they are too simple and one-sided. They both seem now fragments of the same recipe, which was created the milky Way. Eggen and his colleagues read some rows from this recipe, Searle and Zinn — a few others. Therefore, in an attempt to present the history of our Galaxy, we notice friends who have already read one row.
So, it all started shortly after the Big Bang. "Today it is generally believed that the density fluctuations of dark matter gave birth to the first structure, the so — called dark halo. Because of gravity, these structures have not collapsed," — said the German astronomer Andreas Burkert, author of the new model the birth of the Galaxy.Dark halos become the germ — nuclei for the future galaxies. Around them under the influence of gravity to accumulate gas. Was a homogenous collapse, as described by its model ELS. Already using 500-1000 million years after the Big Bang gas accumulations surrounding dark halo, has become the "incubators" of stars. Here there was a small protogalaxies In dense clouds of gas appeared first globular clusters, because the stars here were born hundreds of times more often than anywhere else Protogalaxies collide and merge with each other, so formed large galaxies, including our milky Way. Today it is surrounded by dark matter and halos, consisting of single stars and of globular clusters, these ruins of the universe, whose age is more than 12 billion years.
In protogalactic there were many very massive stars. Less than a few tens of millions of years, as most of them exploded. These explosions have enriched the gas cloud of heavy chemical elements. Therefore, in the galactic disk are not born stars such as in halo — they contain hundreds of times more metal. Additionally, these explosions have created a powerful galactic vortices, which warmed up gas and swept it off protogalactic. There was a division of gas mass and dark matter. It was an important stage of galaxy formation, not taken into account in any model.
Meanwhile, the dark halo are increasingly faced with each other. While protogalaxies stretched or broke. About these disasters resemble a chain of stars, which is preserved in the halo of the milky Way since the days of his youth. Studying their location, it is possible to assess the events that took place in that era. Gradually these stars formed a vast sphere appears to us halo. As it cools down inside of it penetrated the gas cloud. Their angular momentum is preserved, so they are not collapsed into one single point, and formed a rotating disk. All this happened more than 12 billion years ago. Now the gas was compressed as described in the ELS model.
At this time, and formed a "bulge" of the milky Way — its Central part, reminiscent of the ellipsoid. The bulge consists of very old stars. Obviously, it originated with the merger of the largest protogalactic, the longest-held gas clouds. In the middle of it turned out to be neutron stars and small black holes — relics of exploded supernovas. They merged with each other, simultaneously absorbing the gas streams. Perhaps it originated a huge black hole residing in the center of our Galaxy.
The history of the milky Way is much chaotic than previously thought. Our home Galaxy, impressive even by space standards, was formed after a series of shocks and mergers — after a series of cosmic catastrophes. The vestiges of those distant events can be detected today.
For example, not all stars in the milky Way orbit around the galactic center. Obviously, over billions of years of existence, our Galaxy "swallowed" a lot of fellow travelers. Age every ten stars in the galactic halo is less than 10 billion years. By the time the milky Way had already formed. Perhaps it's the remnants captured once dwarf galaxies. A group of British scientists from the Astronomical Institute (Cambridge), headed by Gerard Gilmore has calculated that the milky Way is, obviously, swallowed from 40 to 60 dwarf galaxies of the type of Karina.
In addition, the milky Way attracts a huge mass of gas. So, in 1958, the Dutch astronomers noticed a halo in many small spots. In fact they turned out to be a gas cloud that consisted mostly of hydrogen atoms and raced in the direction of the galactic disk.
Our Galaxy does not temper its appetite continue. Obviously, it will consume next to us dwarf galaxy — Fornaks, Karina and maybe, Sextone, and then will merge with the Andromeda galaxy. Around the milky Way — this insatiable "star cannibal" will become even more desert.
Amazing Picture of the Milky Way Galaxy..