Located 10 billion light years from Earth and potentially comprising thousands of individual galaxies, the megastructure is about 250 trillion times more massive than the Sun.
The cluster, named "IDCS 1426", is the most massive cluster of galaxies yet discovered in the first four billion years after the Big Bang.
According to the team from the Massachusetts Institute of Technology (MIT), University of Missouri, University of Florida and elsewhere, IDCS 1426 appears to be undergoing a substantial amount of upheaval.
The researchers observed a bright knot of X-rays, slightly off-center in the cluster, indicating that the cluster's core may have shifted some hundred thousand light years from its centre.
The core may have been dislodged from a violent collision with another massive galaxy cluster, causing the gas within the cluster to slosh around, like wine in a glass that has been suddenly moved.
"In the grand scheme of things, galaxies probably didn't start forming until the universe was relatively cool, and yet this thing has popped up very shortly after that," said Michael McDonald, assistant professor of physics at MIT.
"Our guess is that another similarly massive cluster came in and sort of wrecked the place up a bit. That would explain why this is so massive and growing so quickly. It's the first one to the gate, basically," he explained.
Galaxy clusters are conglomerations of hundreds to thousands of galaxies bound together by gravity.
They are the most massive structures in the universe, and those located relatively nearby, such as the Virgo cluster, are extremely bright and easy to spot in the sky.
In 2012, scientists using Nasa's Spitzer Space Telescope first detected signs of IDCS 1426 and made some initial estimates of its mass.
"We had some sense of how massive and distant it was, but we weren't fully convinced," McDonald said, adding that the new results are the nail in the coffin that proves that it is what we initially thought.
This cluster is sort of like a construction site - it's messy, loud, and dirty, and there's a lot that's incomplete.
"By seeing that incompleteness, we can get a sense for how [clusters] grow. So far, we've confirmed about a dozen or so galaxies, but we're just seeing the tip of the iceberg, really," McDonald noted.
The scientists may get an even better view of IDCS 1426 in 2018 with the launch of the James Webb Space Telescope - an infrared telescope that is hundreds of times more sensitive than the current Spitzer Telescope that first detected the cluster.
The findings are forthcoming in The Astrophysical Journal.