Clusters of galaxies all throughout the cosmos have ancestors that developed not long after the universe was born. By looking far into the past to investigate so-called “protoclusters,” astronomers can get a better sense of how these ancient structures evolve into newer galaxy clusters, like those seen in our corner of the universe.
The search for protoclusters has recently yielded an exceptional discovery: the most distant proto-supercluster known to date, or in other words, an ancestor of a “cluster of clusters.” This structure, which has a mass 5,000 times that of the Milky Way, not only breaks a remarkable galactic record, but could also serve as a key to understanding how the universe’s earliest galaxy clusters formed and evolved, according to a new study published in The Astrophysical Journal.
“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,” said study author Vandana Ramakrishnan, a graduate student at Purdue University at the time of the study, in a press release. “We also hope to get a better sense of how these protoclusters are connected to the larger cosmic web.”
The Ancestors of Galaxy Clusters
Galaxy clusters are the most massive gravitationally bound structures in the universe, comprising hundreds to thousands of galaxies that span millions of light-years. These clusters are held together by dark matter, the invisible glue that maintains the structure of the whole universe.
Explore All OptionsGalaxy clusters don’t just appear out of nowhere; they evolve from protoclusters, a collection of galaxies that are more loosely bound. Protoclusters are at an earlier stage in formation where they haven’t had enough time to “virialize,” or settle down into a stable state, according to the University of Massachusetts Amherst. They’re rare to find for astronomers because confirming their structure requires observations of many individual galaxies.
Read More: Giant Galaxies Emerged Just 1.4 Billion Years After the Big Bang
Finding Ancient Protoclusters
The team behind the new study embarked on a search for these ancestors of galaxy clusters, hoping to learn how clusters evolve over time.
To find protoclusters, they used data from the One-hundred-deg DECam Imaging in Narrowbands (ODIN) survey. This project uses the Dark Energy Camera (DECam) on the Victor M. Blanco 4-meter Telescope in Chile, which spent more than 100 nights over the last three years scanning the Southern Hemisphere sky.
From the data collected in the ODIN survey, researchers identified 150 distant protoclusters that formed when the universe was about 1–3 billion years old. Two of these protoclusters, named COSMOS-z3.1-A and COSMOS-z3.1-C, were noteworthy because of their overdensity of galaxies.
The researchers then endeavored to make detailed 3D maps of the protoclusters by relying on spectrographs, which use properties of light to measure the distance of objects. The resulting 3D maps allowed the researchers to predict that both COSMOS-z3.1-A and COSMOS-z3.1-C will eventually evolve to be more massive than the largest known cluster in our local universe, the Coma Cluster.
A Record-breaking Supercluster
The researchers were particularly intrigued by COSMOS-z3.1-A, which is even rarer than a typical protocluster. That’s because it's a proto-supercluster that has been observed when the universe was only 2.1 billion years old, making it the earliest, most distant proto-supercluster ever found. As a supercluster, this massive structure contains a collection of smaller clusters.
“COSMOS-z3.1-A represents the most extreme, most overdense regions of the Universe,” said Ramakrishnan. “We think there should be fewer than one such object for every 10,000 galaxy clusters!”
The 3D maps also revealed that protoclusters are clumpy and irregular in shape, indicating that they evolve in a “bottom-up” manner; this means that existing smaller structures merge together, forming larger structures.
According to the researchers, these clumps will collapse together as the protoclusters evolve, which will result in rounder clusters that appear similar to the ones that are in our local universe.
So far, the ODIN survey has helped the researchers decipher galaxy evolution — from distant protoclusters to settled clusters that are closer to us in space and time — but data from the Vera C. Rubin Observatory will open up even more opportunities to study the evolution of galaxies as it continues to scan the Southern Hemisphere sky every few nights.
Read More: Bends and Tears in Stellar Streams May Help Reveal Dark Matter's Influence
Article Sources
Our writers at Discovermagazine.com use peer-reviewed studies and high-quality sources for our articles, and our editors review for scientific accuracy and editorial standards. Review the sources used below for this article:
- This article references information from a study published in The Astrophysical Journal: ODIN: Characterizing the Three-dimensional Structure of Two Protocluster Complexes at z = 3.1
- This article references information from the University of Massachusetts Amherst: Protoclusters: The Grandiose Infants that Shaped the Universe
