Space and Physics
PUBLISHED
Astronomers have discovered the grandparent of all galaxy superclusters – a concentration of galaxies that would be impressive in the local universe now, and is incredible in the early universe.
Over 100 observing nights, astronomers with the ODIN project looked at the southern sky using the Dark Energy Camera on the Víctor M. Blanco 4-meter Telescope in Chile. They discovered 150 distant protoclusters, all from when the universe was between 1 and 3 billion years old.
About 5 to 10 percent of all galaxies live in galaxy clusters, with hundreds if not thousands of members. The clusters sit at the nodes of the cosmic web, the way matter is distributed in the universe.
Understanding how clusters came to be is extremely important, and this was the focus of the ODIN project. Among those 150 protoclusters, they found two that are particularly large and worth doing follow-up observations on.
These two are known as COSMOS-z3.1-A and COSMOS-z3.1-C. The team conducted a spectroscopic analysis, meaning they studied the light of each individual galaxy and estimated its distance. It allowed them to construct a 3D map of these galaxy clusters, and they are both surprising.
Both systems are very rich in galaxies, and models suggest that they are expected to evolve into clusters that are larger than the Coma cluster, the record-holder for the biggest galaxy cluster in the local universe.
If this was not already exciting, COSMOS-z3.1-A appears to be a supercluster, so a collection of galaxy clusters all gravitationally bound with one another. This is the earliest, most distant proto-supercluster known, with the mass of 5,000 Milky Ways.
“COSMOS-z3.1-A represents the most extreme, most overdense regions of the Universe,” lead author Vandana Ramakrishnan, a graduate student at Purdue University at the time of this study, said in a statement.
“We think there should be fewer than one such object for every 10,000 galaxy clusters!”
The finding is in line with theoretical predictions. The idea is that these clusters, and the rarer superclusters, formed bottom-up with clumps of protogalaxies and baby galaxies coming together. The 3D maps in this work suggest that this is indeed the case.
ODIN will expand this analysis to other clusters, refining our understanding of how these massive and important structures came to be.
“With this project, we’re hoping to understand the growth of massive structures in the Universe and how they influence the evolution of galaxies within them,” explained Ramakrishnan. “We also hope to get a better sense of how these protoclusters are connected to the larger cosmic web.”
The study is published in The Astrophysical Journal.
