Astronomers have discovered billions of dwarf galaxies on the cosmic web

With the help of the Very Large Telescope (VLT) of the European Southern Observatory (ESO), astronomers for the first time examined in detail several strands of the cosmic web – the structures of hydrogen gas in which galaxies form. It turned out that these filaments are filled with billions of dwarf galaxies that no one knew about before. The research results are published in the journal Astronomy & Astrophysics.

Although gas filaments, or filaments, in which galaxies are born, have long been predicted by cosmological models, they have not yet been directly observed. Everything that was known about the structure of the cosmic web was limited to a few specific regions along the lines of propagation of the rays of the quasars, which, like car headlights, “flash” gas clouds along the line of sight.

Now, French astrophysicists from the Lyon Center for Astrophysical Research and the University of the Côte d’Azur have directly discovered and studied several strands of the cosmic web using the multifunctional spectroscopic instrument MUSE, installed on the ESO Very Large Telescope in Chile.

MUSE is the main element of the adaptive optics system, which compensates for the blurring of the Earth’s atmosphere and allows, by increasing the contrast, to obtain much clearer images of even very weakly developed objects of the Universe.

For their study, the authors selected a fragment of the so-called Hubble Superdeep Field (HUDF), an image of a small region of space compiled from data obtained by the Hubble Space Telescope from September 24, 2003 to January 16, 2004.

Scientists have observed this site for over 140 hours. It took eight months to prepare for the observation. After that, it took more than a year to process and analyze the data, as well as to image the hydrogen filaments that formed just one to two billion years after the Big Bang.

Although the HUDF is one of the most deeply studied parts of the cosmos, about 40 percent of the galaxies identified by MUSE are unparalleled in Hubble imagery.

The biggest surprise for the researchers was the discovery that the light from the gas filaments comes from a hitherto invisible population of billions of dwarf galaxies with many stars. It was previously believed that this glow is generated by diffuse cosmic ultraviolet background radiation, which, by heating the gas in the fibers, causes them to glow.

Although these galaxies are too faint to be detected individually with modern instruments, their existence will have serious implications for models of the large-scale structure of the universe and understanding how all other galaxies were formed from the gas of the cosmic web, the authors note.

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