The Hubble space telescope – arguably the most successful international cooperation between the European Space Agency (ESA) and NASA – has presented some fascinating new images of the earliest known and faintest galaxies in the universe. These galaxies that are said to have emerged only 600 million years after the Big Bang are the faintest of all the galaxies discovered by Hubble as yet. In a study published in the Astrophysical Journal, an international collaboration of astronomers has determined that these newly observed galaxies were crucial in creating the universe as we know it today.

The team was led by Hakim Atek of the NASA Spitzer Center and the Ecole Polytechnique Fédérale de Lausanne in Switzerland. They have discovered more than 250 tiny galaxies that existed just 600 to 900 million years after the Big Bang. Of the galaxies yet undiscovered at these epochs, this sample of dwarf galaxies is one of the largest. The light from these galaxies took over 12 billion years to reach the telescope, providing astronomers a glimpse into the early years of the universe.

The team has established that the end of the epoch of “reionisation,” was around 700 million years following the Big Bang. Reionisation was marked by the clearance of the thick hydrogen fog that cocooned the early universe.

The team observed the light coming from the galaxies to discover the major role it could have played in the epoch of reionisation – a highly mysterious period in the early history of the universe. Ultraviolet light – the part of the spectrum that soon began to travel large distances without obstruction – was studied as part of the emission from these galaxies. It was determined that the most abundant and smallest of these galaxies could have played a major role in keeping the universe transparent.

Atek, lead author on the study, explained in a Hubble space telescope press release, “If we took into account only the contributions from bright and massive galaxies, we found that these were insufficient to reionise the Universe.” He adds, “We also needed to add in the contribution of a more abundant population of faint dwarf galaxies.”

Mathilde Juazac of the University of KwaZulu-Natal in South Africa and Durham University in UK and co-author on the study, said, “Hubble remains unrivalled in its ability to observe the most distant galaxies. The sheer depth of the Hubble Frontier Field data guarantees a very precise understanding of the cluster magnification effect, allowing us to make discoveries like these.”

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