Gas reservoirs spotted around early galaxies for the first time
A trio of galaxies dating from when the Universe was only a few hundred million years old have surrounded themselves with gas that will grow future stars, according to new images from the James Webb Space Telescope (JWST).
The gas reservoirs are the first to have been observed around such young galaxies.
The trio of galaxies are so far away that we see them as they were when the Universe was just 400 to 600 million years old.
They appear as little more than red smudges: their true nature only becomes apparent when observed with JWST’s near-infrared spectrometer, NIRSpec, which can pick out the light absorbed or emitted by gas within the galaxies.
These spectra showed that the galaxies are surrounded by dense clouds of almost pure hydrogen and helium, the earliest elements to exist in the cosmos.
“The gas must be very widespread and cover a very large fraction of the galaxy,” says Darach Watson from the University of Copenhagen, Denmark, who took part in the study.
“This suggests we are seeing the assembly of neutral hydrogen gas into galaxies. That gas will go on to cool, clump and form new stars.
“The fact we are seeing large gas reservoirs also suggests that the galaxies have not had time to form most of their stars yet.”
The galaxies date from a time known as the Era of Reionisation.
Before this, the gas of the Universe was largely opaque; it wasn’t until the light from newly formed galaxies began to ionise the surrounding gas that it became transparent.
“We’re moving away from a picture of galaxies as isolated ecosystems. At this stage in the Universe’s history, galaxies are all connected to the intergalactic medium with its filaments and structures of pristine gas,” says Simone Nielsen, also from the University of Copenhagen, who also took part in the study.