Hubble captures earliest galaxies

A study using Hubble Space Telescope data has allowed astronomers to peer into the early beginnings of the Universe, including the mysterious period known as the 'epoch of reionisation'.

An image from Hubble showing galaxy cluster MACS J0416.1–2403. It is one of six being studied by the Hubble Frontier Fields programme.
Credit: NASA, ESA and the HST Frontier Fields team (STScI)

Images captured by the Hubble Space Telescope have enabled astronomers to reveal the largest sample of the faintest and earliest known galaxies in the Universe, some of which formed just 600 million lightyears after the Big Bang.
Over 250 have been discovered in all and the light from these dwarf galaxies took over 12 billion years to reach the telescope. This has enabled the team behind the study to peer into the early beginnings of the Universe and learn more about how these small galaxies contributed to its evolution and development.
The study was led by Hakim Atek of the Ecole Polytechnique Fédérale de Lausanne (EPFL) in Switzerland.
“The faintest galaxies detected in these Hubble observations are fainter than any other yet uncovered in the deepest Hubble observations,” says Johan Richard from the Observatoire de Lyon, France.
The light from these early galaxies could have played a huge role in the epoch of reionisation, according to the team. This was the stage at which the thick hydrogen fog present in the early Universe began to clear and ultraviolet light was able to travel over larger distances without being blocked. This mysterious event also saw the formation of the first radiating bodies in the cosmos and, eventually, the Universe as we now know it.
Hubble data has allowed the team to determine that the smallest and most abundant galaxies in the study could have played a major part in this creation of transparency throughout the Universe. As well as this, the team were able to establish that the epoch of reionisation was completed about 700 million years after the Big Bang.
Atek says: “If we took into account only the contributions from bright and massive galaxies, we found that these were insufficient to reionise the Universe. We also needed to add in the contribution of a more abundant population of faint dwarf galaxies.”
The team used the deepest images of gravitational lensing made so far in three galaxy clusters, taken as part of the Hubble Frontier Fields programme. These clusters generate gravitational fields that magnify light from the faint galaxies far behind them. This enables astronomers to study the first generation of galaxies in the Universe.
Jean-Paul Kneib, co-author of the study and also from EPFL, says: “Clusters in the Frontier Fields act as powerful natural telescopes and unveil these faint dwarf galaxies that would otherwise be invisible.”



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