Vigorous star-forming galaxy at cosmic dawn discovered

"A number of galaxies were actively forming stars long after the Big Bang, and some of them were comparable to or even more active than GN-108036. The significant finding about GN-108036 is that it demonstrates the existence of a vigorous star-forming galaxy when the Universe was still very cold and dark,” Team leader Masami Ouchi at the University of Tokyo said.

This research will be published in the Jan. 10 issue of The Astrophysical Journal.

Several teams of astronomers have reported discoveries of compact and massive old galaxies around four billion years after the Big Bang. How they formed remains a mystery. Small, actively star-forming galaxies like GN-108036 might be the ancestors of such galaxies. Detailed investigations of the nature of GN-108036 will provide us with an important key for understanding the early phases of the formation and evolution of galaxies, the team said.

Ouchi’s team obtained the spectra of GN-108036 and calculated its distance from Earth to confirm that it is one of the most distant galaxies ever discovered.

A review of archival images revealed the occurrence of remarkably energetic star formation within it; a large mass of gas, equivalent to about a hundred Suns per year, was forming stars. Although nine galaxies from about 600 to 800 million years after the Big Bang have been confirmed to date, GN-108036 was forming stars much more vigorously than the other galaxies.

About 380,000 years after the Big Bang, a decrease in the temperature of the Universe caused electrons and protons to join to form neutral hydrogen. The Universe entered its "dark age" at this time.

Bahram Mobasher, a team member from the University of California, Riverside, explained how the dark age ended: "It ended when gas clouds of neutral hydrogen collapsed to generate stars, forming the first galaxies, which probably radiated high-energy photons and reionized the Universe. Vigorous galaxies like GN-108036 may well have contributed to the reionization process, which is responsible for the transparency of the Universe today.”

"The amount of stars born every year was more than ten times higher than those in the other galaxies at a comparable distance," explained Ono. "We're surprised to know that such a vigorous galaxy existed at a time when the Universe was only five percent of its present age."