A major discovery 8.4 billion light years from Earth stuns scientists Technical news

Astronomers have discovered the most distant galaxy cluster and that’s the mostrelaxed‘ one they have seen before.

This galaxy cluster, called SPT-CL J2215-3537 (SPT2215 for short), is the most distant ever observed that has not been disrupted by violent collisions with other galaxy clusters.

SPT2215 is about 8.4 billion light-years from Earth and was seen when the universe was only 5.3 billion years old, compared to its current age of 13.8 billion years.

This means that SPT2215 got a head start in its formation compared to other clusters of a similar size, and that it has been “tilted” over the past billion years, allowing it to relax.

Astronomers estimate that the cluster has a mass about 700 trillion times that of the Sun.

Galaxy clusters are collections of tens to hundreds of galaxies, along with vast amounts of hot gas and dark matter, filling the space between galaxies, all held together by gravity.

They grow over time by merging with other galaxy clusters, causing perturbations in the cluster gas. However, if given enough time to “relax” without merging, the gas can take on a smooth, relaxed appearance.

Teams of scientists used data from NASA’s Chandra X-ray Observatory, their retired Spitzer Space Telescope, the National Science Foundation/Department of Energy South Pole Telescope, and the Dark Energy Research Project in Chile.

“Until now, we have not seen a relaxed galaxy cluster as distant as SPT2215,” said Michael Calzadilla of the Massachusetts Institute of Technology (MIT), lead author of the latest of three papers confirming that the cluster is relaxed.

At the center of SPT2215 is a large galaxy containing a supermassive black hole at its center. Calzadilla’s report found massive amounts of new stars forming in this large galaxy. Star formation in the cluster’s central galaxy is fueled by the cooling of hot gas as the cluster relaxes.

The behavior of the giant black hole at the center of the cluster affects how quickly the gas cools to form stars.

If the black hole produces too many powerful bursts, then most of the gas in the cluster cannot cool enough to form a stream of new stars. Unlike most quiescent clusters observed with Chandra, the giant black hole in SPT2215 does not appear to prevent such cooling.

“The black hole in SPT2215 appears to be quiet enough to allow star formation to flourish,” said Michael McDonald, co-author of all three studies.

Another key feature of SPT2215 is the isolation of its central galaxy. There are no other galaxies within about 600,000 light years that are as bright or extended.

Thus, the cluster has not undergone a merger with another cluster in the last billion years, providing further evidence that SPT2215 is relaxed.

Scientists weren’t sure they’d find a galaxy cluster that had been loosened at this age from the universe, because they’re usually still undergoing shocks from mergers with other clusters or groups of galaxies as they grow in size.

“The fact that this cluster is so massive, so early in the universe, suggests a really exciting, fast formation history,” said Lindsay Bleem of the US Department of Energy’s Argonne National Laboratory in Lemont, Illinois, whose team first reported spotting the cluster in 2020.

“Yet the fact that he is relaxed suggests otherwise. It would be like finding a tidy kitchen right after a quick dinner.

These SPT2215 results match well with those from NASA’s James Webb Space Telescope, which showed that galaxies form at a very early age.

“Quiet clusters like SPT2215 are one of the telltale signs that have been used to measure the expansion of the universe,” said Adam Manz of Stanford University, who first reported SPT2215’s quiescent state using Chandra data in 2022.

“Adding distant objects like this to our sample of relaxed clusters allows us to better constrain the acceleration of the cosmic expansion and the properties of the dark energy that drives it.”