Observations of the so-called extragalactic background radiation have helped Russian astrophysicists find out how long the largest “starry nurseries” live within the Milky Way. Their conclusions were presented in the journal MNRAS.
“We have known for a long time that the main part of ultraviolet radiation is produced by stars, and infrared radiation and young stars are born in giant molecular clouds from dust particles.” However, it remained unclear which parameters of the evolution of stars and clouds are essential for background study and which are not “, Explains Grigory Rubtsov from the Institute for Nuclear Research of the Russian Academy of Sciences in Moscow, whose words are quoted by the press service of the Russian Science Foundation.
Extragalactic background light (EBL) is the ultraviolet, visible and infrared radiation left over from the era of the formation of the first stars. Unlike the cosmic microwave background left after the Big Bang, this kind of electromagnetic waves is extremely difficult to detect – it is “clogged” by the powerful radiation of modern stars and galaxies.
However, “seeing” extragalactic radiation is very important for astronomers, since this will allow you to look into the most ancient history of the universe. Scientists believe that background radiation originated in the era of 300 thousand to a billion years after the Big Bang, during the so-called “era of reionization.” At this time, the universe once again became transparent due to the fact that its neutral atoms of the universe turned into ions under the influence of the light of the first stars.
Rubtsov and his colleague Alexander Korochkin approached the disclosure of the secrets of the first stars of the universe, trying to understand how modern giant molecular clouds, the largest “star crèche” of the Milky Way and other galaxies, can interfere with extragalactic background radiation.
Russian astrophysicists drew attention to the fact that the “echo” of the light of the first stars will be small, but differ in their arrangement and spectrum from the glow produced by the largest clouds of dust and gas in the Milky Way and in other galaxies. In particular, the latter will produce most of the light in the infrared range, while extragalactic background radiation will be more pronounced in the ultraviolet and visible part of the spectrum.
Accordingly, knowing the mass of these clouds and the speed of star formation, you can accurately calculate the strength of EBL, and vice versa – knowing the approximate power of glow of the first stars of the Universe, one can learn how the largest “star cribs” of the Galaxy and its neighbors work. The problem is that neither one nor the other parameter is as yet impossible to calculate accurately.
Korochkin and Rubtsov approached the solution of this problem by creating a computer model of the Milky Way, which takes into account the differences in the nature of the glow of giant molecular clouds and the first stars of the universe. By accidentally changing their properties, scientists tried to make a virtual copy of our Galaxy the most similar to what it really looks like, which allowed them to uncover some of the features of its largest stellar “maternity homes.”
As it turned out, a typical giant molecular cloud lives about 6 million years and has a radius of about 20 light years. This is noticeably smaller than the largest “star crib” of the surrounding Universe – the Orion clouds in the Milky Way and the Tarantula Nebula in the Large Magellanic Cloud, whose length is hundreds of light years.
Such clouds, as calculations of scientists show, began to appear in the Universe no later than 1.5 billion years after the Big Bang, which corresponds to the generally accepted theories about the evolution of galaxies. Otherwise, as Korochkin concludes, the universe simply could not accumulate the necessary number of stars so that all galaxies looked today as we see them in the night sky.