Astronomers have determined that our galaxy, the Milky Way galaxy, is a natural zombie. Of course, she chases after anyone and does not feed on the "brains" of neighboring galaxies, nevertheless, she really has already died once, but the "flame of life" in her bowels managed to flare up again.
And such an unexpected conclusion of Japanese scientists was prompted by a chemical analysis of the composition of the stars included in the Milky Way.
All stars in the Milky Way can be divided into two different groups based on their chemical composition. In the stars of one group, there is an increased concentration of alpha elements, which include oxygen, magnesium, silicon, sulfur, calcium and titanium. The concentration of alpha elements in the stars of the second group is much lower, but a much larger amount of iron is observed in their composition. The existence of two types of stars implies that different processes occur during their formation, but the exact "cosmic mechanism" of this was unclear until recently.
Astronomer Masafumi Noguchi and his colleagues at Tohoku University conducted computer simulations that spanned 10 billion years ago, the results of which provide an answer to the question raised above. The two types of stars represent two periods of star formation, which were separated by a time interval when the intensity of the formation of new stars in our galaxy was practically zero.
The mathematical model originally used by the Japanese was intended for the study of galaxies larger than the Milky Way. The chemical composition of stars directly depends on the chemical composition of the gas clouds from which they formed. It is known that in the early stages of the existence of the Universe, there were very few heavy elements such as metals in it. These elements were formed later as a result of supernova explosions, which "scattered" the elements across the vastness of galaxies.
At the first stage of its development, the galaxy attracts and accumulates in its volume cold gas from the surrounding space. And, thanks to the accumulations of this gas, the first generation of stars begins to appear in the galaxy. Stars, consisting of light elements, are short-lived on cosmic time scales, after about 10 million years they explode, turning into Type II supernovae and scattering alpha elements that have arisen in their depths around the surrounding space.
Stars that already have a fairly high concentration of alpha elements have been around for much longer. But according to the simulation results, something went wrong in the Milky Way galaxy after 3 billion years after its formation. "As a result of intense supernova explosions, powerful shock waves arose, the energy of which heated up the clouds of cosmic gas to a high temperature," the researchers write, "And, because of this, about 7 billion years ago, new stars practically stopped forming in our galaxy."
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This "pause" lasted about 2 billion years, and its end was marked by the outburst of Type Ia supernova explosions, into which stars turn, the lifetime of which is at least 1 billion years. It is during these explosions that iron and other metals are formed. When the gas from the last wave of explosions cooled, which happened about 5 billion years ago, the intensity of star formation processes took off again, but as a result of these processes, stars began to appear, in which a large concentration of iron and other metals is observed. Note that our Sun belongs to this second generation of stars, which is now about 4.6 billion years old.
Note that the reliability of Masafumi Noguchi's model has already been tested on the results of studies of our neighboring galaxy, the Andromeda galaxy. The processes of stellar formation in the Andromeda galaxy also proceeded in two stages, separated by an intermediate "dead" stage. And if scientists manage to get additional confirmation of Masafumi Noguchi's model, this will force them to reconsider some of the existing theories that exclude the possibility of a "dead" period in the formation of massive galaxies.