New observations with the Atacama Large Milimeter / Submillimeter Array (ALMA) further delay the formation of massive galaxies by identifying a pair of giant galaxies that form in a star shape, when the Universe was only 780 million years old or about 5% of your current age. The research appears in the journal Nature .
Galaxies, collectively known as SPT-S J031132-5823.4 (SPT0311-58 for short), were originally identified as a single light source by the South Pole Telescope in Antarctica.
These early observations indicated that the object was very distant and shone brightly with infrared light, which means it was extremely dusty and probably was going through an explosion of star formation.
Subsequent observations of ALMA revealed the distance and dual nature of SPT0311-58, clearly resolving the pair of interacting galaxies.
The largest of the pair is forming stars at a rate of 2,900 solar masses per year, contains 270 billion solar masses of gas and 2.5 billion solar masses of dust.  It is the most gigantic galaxy ever seen inhabiting the Universe during the first billion years after the Big Bang.
Its fast star formation is probably triggered by its companion galaxy in a projected separation of 26,100 ligh t-years.
The companion is also not light and comprises approximately 40 billion solar masses of gas and dust.
"Any of these galaxies alone would be extreme, and here you have two together." said Dr. Chris Hayward, a researcher at the Center for Computational Astrophysics at the Flatiron Institute.
"The two galaxies are so close that they will soon merge to form the largest galaxy ever observed in that period in cosmic history," the astronomers said.
Based on the amount of gas in the two galaxies and the typical ratio of dark to ordinary matter in galaxies, Dr. Hayward and the co-authors calculated the extent of the dark matter halo that contains the two galaxies.
"The estimated mass of the halo of 1 billion times the mass of the Sun is conservative, and the actual number may be higher," said Dr. Hayward.
This discovery provides new details about the appearance of large galaxies and the role that dark matter plays in the assembly of the most massive structures in the Universe.
"The colossal collection of ordinary dark matter is not just a record-breaking curiosity," said Dr. Dan Marrone of the University of Arizona in Tucson.
"The merged galaxies will now serve as a test bed for astronomers to study how massive the star-forming galaxies evolved during the early stages or f the Universe, there is still more work to be done."
D.P. Marrone et al. . Growth of the galaxy in a massive halo in the first billion years of cosmic history. Nature published online on December 6, 2017; doi: 10.1038 / nature24629