An international team led by the astronomer Hakim Atek of the Ecole Polytechnique Fédérale de Lausanne, Switzerland, used the Hubble Space Telescope to observe over 250 dwarf galaxies that existed between 600 and 900 million years after the Big Bang. It’s one of the largest samples of dwarf galaxies discovered so far dating back to such a remote era and allows us to look into the universe at a young age providing useful information to understand its evolution.

The astronomers studied images of the Abell 2744, MACSJ0416.1-2403 and MACSJ0717.5+3745 galaxy clusters taken within the Hubble Frontier Fields programme. That’s a 3-year survey that aims to get the deepest observations of the universe using the gravitational lensing effects of six galaxy clusters to explore more distant regions.

The three galactic clusters have such a gravity that they distort the light from more distant galaxies, acting like a huge magnifying glass. This allowed to see the light from dwarf galaxies that are more than 12 billion years old. Some of these galaxies have the faintest light ever detected by the Hubble Space Telescope.

According to the astronomers who conducted this research, the light emitted by these ancient galaxies may have had a significant importance in the so-called period of reionization. It’s a period when the light of the first stars interacted with the gas present in great abundance in the universe ionizing it and then separating the electrons from the protons.

One of the consequences of the reionization was that the universe was made transparent. Observing the ultraviolet light coming from the ancient galaxies observed, the astronomers established that that era ended about 700 million years after the Big Bang. One of the problems in the dating of that era was given the scarcity of galaxies but the discovery of a large number of dwarf galaxies helps solve it.

This result can be combined with those obtained in a completely different way by ESA’s Planck Surveyor space probe. In that case, the scientists analyzed a map of the polarization of the cosmic microwave background radiation dating back to the early stages of the universe life.

The results of this research are to be published in the journal “Astrophysical Journal”. They confirm that taking advantage of the gravitational lensing effect of galaxy clusters can allow to achieve extraordinary observations of extremely distant galaxies. This is very useful for this research on the origins of the universe.

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