For the first time ever, astronomers using the James Webb Space Telescope (JWST) may have detected some of the earliest galaxies in the known universe in the midst of being born.
In a new study, published Thursday (May 23) in the journal Science, the researchers report the detection of what appears to be three infant galaxies sprouting from a primordial cloud of hydrogen and helium gas just 400 to 600 million years after the Big Bang.
According to the authors, this discovery could open a window into the murky period known as the era of reionization — a time when the earliest stars and galaxies first began to pierce the dark, dense clouds of gas around them and thus reveal the transparent universe we know today.
"These galaxies are like sparkling islands in a sea of otherwise neutral, opaque gas," lead study author Kasper Heintz, an assistant professor of astrophysics at the Cosmic Dawn Center (DAWN) at the University of Copenhagen, said in a NASA statement. "Without Webb, we would not be able to observe these very early galaxies, let alone learn so much about their formation."
In the study, the researchers used JWST to look at 12 known early galaxies dating to no more than 600 million years after the Big Bang. Back then, our now 13.8 billion-year-old universe was about 3% of its current age. The team specifically hunted for galaxies in which radiation was being absorbed by the dense clouds of electrically neutral hydrogen gas that pervaded the universe at that time. Such absorption would indicate that the galaxies were actively weaving that gas into new stars.
By looking at the ancient galaxies' spectra, or the different wavelengths of light they emitted, the team found evidence that light from three of them was being absorbed by large amounts of neutral hydrogen gas.
"This suggests that we are seeing the assembly of neutral hydrogen gas into galaxies," study co-author Darach Watson, also of DAWN, said in the statement. "That gas will go on to cool, clump, and form new stars."
That early star formation was crucial for pulling the universe out of the so-called cosmic dark ages and into the era of reionization. As stars and galaxies emerged from the dense gas clouds of the early universe, their stellar radiation ionized, or charged, the gas around them, slowly transforming space from a thick soup of opaque hydrogen into the clear and transparent cosmos we see now.
JWST has spotted ancient galaxies from this era before, but this is the first time that astronomers have witnessed "their very birth, and thus, the construction of the first star systems in the universe," Heintz said in a University of Copenhagen statement.
If these findings are confirmed with follow-up observations with JWST, they may allow astronomers to answer crucial questions about the nature of the gas clouds that once obscured the universe, and how the first galaxies emerged to enlighten them.
