Using the Euclid Space Telescope, scientists have discovered a staggering 1.5 trillion orphan stars moving through a vast cluster of thousands of galaxies, one of the largest structures in the cosmos.
These orphaned stars, torn from their own galaxies, fill the space between the Perseus cluster galaxies with a ghostly blue light. This so-called “inner cluster” light is so faint that it is many thousands of times darker than the night sky above Earth.
By observing this intracluster light in the Perseus cluster, which is 240 million light-years from Earth and has a mass equivalent to about 650 trillion suns, Euclid can help scientists better understand where the faint light component of galactic galaxies comes from. clusters and the origin of the cosmic orphans that emit it.
Connected: The ‘dark universe detective’ Euclid telescope has revealed new images of space – and they’re remarkable
Euclid launched from Cape Canaveral, Florida atop a SpaceX Falcon 9 rocket on July 1, 2023. Euclid’s primary mission is to study dark energy, the mysterious force accelerating the expansion of the universe, and dark matter, an “invisible” substance that does not interacts with light and is not made up of atoms like the “everyday” things that surround us.
However, despite being designed to peer into the invisible ‘dark universe’, the telescope was also able to detect light emanating from between galaxies in the Perseus galaxy cluster.
“We were surprised by our ability to see so far into the outer regions of the cluster and distinguish the subtle colors of this light,” team leader and University of Nottingham scientist Nina Hatch said in a statement. “This light can help us map dark matter if we understand where the intracluster stars come from. By studying their colors, brightness and configurations, we found that they originate from small galaxies.”
Orphan stars have the blues
The key to understanding the orphan stars in Perseus was Euclid’s ability to see the faintest light in the cluster, the intracluster light that comes not from its galaxies but between them.
“This diffuse light is more than 100,000 times fainter than the darkest night sky on Earth,” said team member and Max-Planck Institute for Extraterrestrial Physics Matthias Kluge. “But it’s spread out over such a large volume that when we add it all up, it accounts for about 20% of the luminosity of the entire cluster.”
The orphan stars seen by Euclid in the Perseus cluster are distinguished by their characteristic blue coloration and their loose grouping. These characteristics allowed Hatch and colleagues to trace their origins.
The team found that some of these free-roaming stars in the intracluster space were abducted from the fringes of galaxies by interactions with other galaxies. Other orphan stars they found came from smaller dwarf galaxies in the Perseus cluster that were completely destroyed.
What the team found next surprised them. After being torn from their home galaxies, intracluster stars are expected to begin orbiting the largest galaxies in the cluster where they find themselves isolated, almost like a lost child in the mall gravitating toward the nearest adult.
However, Hatch and colleagues did not find this in Perseus with Euclid. Instead, they saw the orphan stars orbiting a point between the cluster’s two brightest galaxies, NGC 1275 and NGC 1272.
“This new observation suggests that the massive Perseus cluster may have recently undergone a merger with another group of galaxies,” said team member and University of Nottingham astronomer Jesse Golden-Marks. “This recent merger could cause a gravitational perturbation that would cause either the most massive galaxy or the orphan stars to deviate from their expected orbits, leading to the observed discrepancy.”
The same researchers also used Euclid’s sensitive visible-light capabilities to spot 50,000 free-flying densely packed and spherical collections of tens of thousands to millions of stars called “globular clusters” in the Perseus galaxy cluster. The diffuse intracluster light appears to be distributed in a manner similar to the globular clusters in Perseus, so these conglomerations of stars appear to be the source of at least some of this light.
Stars in these globular clusters do not have high concentrations of “metals,” a term astronomers use for elements heavier than hydrogen and helium. This means to the team that the globular clusters in the Perseus galaxy cluster have made their way inward from the vast collection of outer edge galaxies, which are also “metal-poor”.
Globular clusters are a dominant factor in dwarf galaxies, meaning that some of the intracluster light may originate from the remnants of such small galaxies that have been torn apart by tidal forces generated during encounters with more massive galaxies.
The team also found from the Euclidean observation of Perseus that the small dwarf galaxies in this galaxy cluster increase in number as one moves away from the center of the cluster.
The research helps verify Euclid’s ability to understand the evolution of galaxies and galaxy clusters, and thus how the universe came to be the way it appears to us today.
Excitingly, these findings are among the first science results from Euclid’s Early Release Observations, representing just the first 24 hours of Euclid’s observations before it begins observing its primary science targets, billions of galaxies across more than a third of the sky on February 14, 2024. .
The team’s research is featured on the paper repository site arXiv.