Astronomers have discovered two giant galaxies that existed in the young universe and are surrounded by a whole "ocean" of dark matter, whose mass is trillions of times the weight of the sun, according to an article published in the journal Nature.
“We used to think that during the youth of the Universe it was inhabited by many small galaxies, which gradually ionized the intergalactic medium and made it transparent to light and other forms of radiation. Recent images from ALMA have helped to find out that this is not so, and once again push back the time when the first really large galaxies appeared in the Universe,”said Daniel Marrone of the University of Arizona at Tucson (USA).
The first galaxies, according to scientists, appeared as a result of the direct gravitational collapse of giant gas clouds that arose in the void of the Universe due to small irregularities in the distribution of matter generated by the gravitational "echo" of the process of the superfast expansion of the Universe after the Big Bang.
Some of these clouds turned into single galaxies, while others, larger ones, became the ancestors of tens and hundreds of "star megacities", united into clusters and superclusters. At the end of the last century, theoretical astronomers suggested that the first galaxies that emerged in the first billion years of the existence of the Universe should have been small in size and mass.
In recent years, as Murone notes, these theories have begun to be questioned - Hubble, ALMA and other powerful telescopes are constantly discovering more ancient and large galaxies that existed almost at the same time when the first stars appeared, and the Universe became completely transparent and accessible for observation.
Marrown and his colleagues accidentally discovered a pair of giant galaxies that would not fit these theories in principle when they studied stars and other light sources observed by the SPT infrared telescope at the South Pole. Its main goal is to search for distortions in the microwave "echo" of the Big Bang, arising from its interaction with large clusters of galaxies.
Every time the SPT finds large enough clusters, astronomers measure their distance with the ALMA microwave telescope, which can track the movement of even the coldest molecules. During one of these routine measurements, Murrow and his colleagues discovered that the SPT0311-58 cluster, found by SPT in the constellation of Hours and located at a great distance from Earth, is actually gigantic in size.
Calculations show that astronomers see this cluster in the state in which it was 13 billion years ago, about 780 million years after the Big Bang. The cluster consists of two large galaxies, comparable in size to the Milky Way. Each of them is 40 and 270 billion times heavier than the Sun. A noticeable part of this mass, as scientists note, is stardust, the presence of which in early galaxies astronomers previously doubted.
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The close proximity of these galaxies and the high speed of gas flows, in turn, suggests that they are surrounded by a kind of "ocean" of dark matter, preventing stars and other clusters of matter from "escaping" from SPT0311-58. Its mass, according to Marrow, is at least a trillion times that of the Sun, and these are the most conservative estimates.
As noted by scientists, such values exceed the maximum mass for dark matter "bagels" that surround all known galaxies. Murrow and his colleagues hope that the discovery of other objects of similar size will help determine if SPT0311-58 is an exception to the rule or a typical inhabitant of the young universe.
