Japanese astronomers using the Subaru Telescope in Hawaii have discovered an enormous cloud of neutral hydrogen extending for 160 million light-years, the largest structure in that epoch, 11.5 billion years ago. This is not just huge in human terms, the new object is huge in cosmic terms, too. It’s 80 times the distance to Andromeda and would fit 1,600 Milky Ways across it.
The region of the sky was chosen because of the presence of a known proto-supercluster, SSA22. The researchers used the light from the galaxies in SSA22 to study the faint gas clouds but they weren't expecting gas extending within, around and outside the cluster. This discovery is reported in the Monthly Notices of the Royal Astronomical Society.
"We are surprised because the dense gas structure is extended much more than expected in the proto-supercluster," team leader Dr. Ken Mawatari, from Osaka Sangyo University, said in a statement.
"Wider field observations with narrow-band filters are needed to grasp the full picture of this largest structure in the young Universe," he added. "This is exactly the type of strong research that can be done with Hyper Suprime-Cam (HSC) recently mounted at the Subaru Telescope. We intend to study the gas-galaxy relation in various proto-superclusters using the HSC."
The standard model of cosmology expects that structures in the universe should be smaller, and then over time aggregate and merge into larger structures. The gas cloud is definitely an unexpected sight in that early epoch as it's as big as the large superclusters found in the universe today.
The size is not the only intriguing fact. The team also showed that the gas distribution doesn’t align perfectly with how the galaxies are spread out in the proto-supercluster, although it fills the intergalactic space between the cluster. The whole cluster affects the gas distribution.
The research hints at a new relationship between neutral gas and galaxy clusters in the early universe and the team anticipate more investigations in this area.