The small mass and faint emission make dwarf galaxies difficult to study. Recently, a team of astrophysicists used the James Webb and Hubble Space Telescopes, as well as gravitational features in the Pandora cluster, to learn about the role of dwarf galaxies after the Big Bang.

It was dark in the early universe because hydrogen atoms had already formed (interstellar gas was later formed from them, for example), but neither stars nor galaxies had yet emerged from them. The residual radiation was largely absorbed by the still unionized gas. But soon two significant periods (recombination and reionization), each lasting several hundred million years, transformed the universe into almost the one we are accustomed to.

During the recombination period (378 million years after the Big Bang), free electrons and protons combined to form the first atoms (neutral hydrogen atoms), the universe became transparent and cooled rapidly. And in the process of reionization (previously believed to have occurred 600-800 million years after the Big Bang), hydrogen atoms formed ions, and gravitational pull formed stars, galaxies, quasars and other large cosmic objects from interstellar gas.

In cosmology, there is disagreement among researchers about the sources of reionization. More than 30 authors recently joined forces to answer this question and published a study in Nature. Astrophysicists have discovered that the main sources of reionization are dwarf galaxies. Previously, in some models of the evolution of the universe, quasars were considered sources of reionization due to their strong ionizing radiation.

Dwarf galaxies have far fewer stars than the Milky Way and vary in brightness by a factor of about 100. The dimness of low-mass galaxies complicates spectroscopic studies. In a recently published paper, astrophysicists examined eight dwarf galaxies in the Pandora cluster using the James Webb Space Telescope and the Hubble Space Telescope. The accretion of galaxies played the role of a gravitational lens, allowing to increase the radiation flow from objects.

Scientists have discovered that faint dwarf galaxies produced ionizing radiation four times more intense than previously thought during the billion years after the Big Bang. In other words, the ionizing radiation from dwarf galaxies is sufficient to reionize the Universe. At the same time, a small fraction of photons (five percent) do not interact with neutral atoms, which will not interfere with the reionization process, according to scientists. The researchers indicate that the redshift value for this epoch is six (z = 6, which is equivalent to 0.929639 billion years after the Big Bang).

The redshift value is needed to obtain more information about the reionization period. Indeed, in a study published in the Astronomical Journal in 2001, the authors suggested that at z = 6 the universe was approaching the end of reionization.

“It is now well established that faint galaxies are the dominant source of UV radiation during the reionization period,” the study authors emphasize.

The question of what exactly makes the universe transparent to radiation again (that is, ionizes the hydrogen in it) is important, because the answer to this question depends on understanding the entire evolution of the universe. If it was made by quasars (the active surroundings of massive black holes), the completion date of reionization would be one, and if it was made by dwarf galaxies, it would be completely different.