Using the Subaru Telescope in Japan, an international team of researchers has discovered 80 young galaxies that existed in the early universe about 1.2 billion years after the Big Bang.
The team made detailed analyses of imaging data of these galaxies taken by the Advanced Camera for Surveys (ACS) on the Hubble Space Telescope.
At least 54 of the galaxies are spatially resolved in the ACS images. Among them, eight galaxies show double-component structures and the remaining 46 seem to have elongated structures.
The researchers then questioned as to whether the remaining 46 elongated-structured galaxies are really single galaxies.
They found, through computer simulations, that most of the galaxies that were observed as single sources in the Hubble images are actually two merging galaxies.
However, the distances between two merging galaxies are so small they cannot be spatially resolved, even by the high resolution.
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The research suggests that 1.2 billion years after the Big Bang, galactic clumps in the young universe grow to become large galaxies through mergers, which then causes active star formation to take place.
In the present universe, at a point 13.8 billion years after the Big Bang, there are many giant galaxies like our Milky Way, which contains about 200 billion stars in a disk a hundred thousand light years across.
However, there were definitely no galaxies like it in the epoch just after the Big Bang.
While the wide field of view of the Subaru Telescope has played an important role in finding such young galaxies, the high spatial resolution of the Hubble was required to investigate the details of their shapes and internal structures, the authors noted.
This research was conducted as part of the treasury programme of Hubble Space Telescope (HST) called "Cosmic Evolution Survey (COSMOS)".