by Using the Euclid space telescope, scientists have discovered 1.5 trillion giant orphan stars drifting through a massive cluster of thousands of galaxies, one of the largest structures in the cosmos.
These orphan stars, ripped free from their own galaxies, are filling the space between the Perseus cluster galaxies with a gorgeous blue light. The so-called “intracluster” light is so faint that it is thousands of times darker than the night sky on Earth.
By observing this intracluster light in the Perseus cluster, which is located 240 million light-years away from Earth and has a mass equal to about 650 trillion suns, Euclid may help scientists better understand where the light component comes from. from galaxy clusters and the origin of the cosmic orphans that release it.
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Euclid launched from Cape Canaveral in Florida aboard a SpaceX Falcon 9 rocket on July 1, 2023. Euclid’s primary mission is to investigate dark energy, the mysterious force that accelerates the expansion of the universe, and dark matter, an “invisible” substance that cannot does. t interacts with light and is not made up of atoms like the “everyday” stuff around us.
However, despite being designed to peer into the invisible “dark universe”, the telescope was also able to detect light coming 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 recognize 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 intercluster stars came from. By studying their colors, brightness and formations, we discovered that they came 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, which comes not from its galaxies but from its galaxies.
“This diffuse light is more than 100,000 times smaller than the darkest night sky on Earth,” said team member and Max-Planck Institute for Extraterrestrial Physics Matthias Kluge. “But it’s spread over such a large number that when we add it all up, it’s about 20% of the luminosity of the entire cluster.”
The orphan stars seen by Euclid in the Perseus cluster can be identified by their characteristic blue coloration and loose clustering. These features allowed Hatch and colleagues to trace their origins.
The team determined that some of these free stars wandering in space within the galaxy’s periphery were drawn in by interactions with other galaxies. Other orphan stars they found came from smaller dwarf galaxies in the Perseus cluster that were completely disrupted.
The next thing the team discovered surprised them. Once torn from their home galaxies, intracluster stars are expected to begin orbiting the larger galaxies in the cluster they are isolated from, almost like a lost child in the mall reaching for the nearest adult.
Hatch and colleagues did not find that in Euclid’s Perseus, however. Instead, they saw that the orphan stars orbited a point between the two brightest galaxies in the cluster, NGC 1275 and NGC 1272.
“This new observation suggests that the massive Perseus cluster may have recently merged with another group of galaxies,” said team member and University of Nottingham astronomer Jesse Golden-Marx. “This recent merger could have caused gravitational disturbances, which would have caused the larger galaxy or the orphan stars to deviate from their expected orbits, causing the observed misalignment.”
The same researchers also used Euclid’s sensitive visible light capabilities to see 50,000 densely packed and spherical collections of thousands and millions of stars called “globular clusters” in the Perseus galaxy cluster. The diffuse intracluster light appears to be distributed in a similar manner to the globular clusters in Perseus, so it appears that these star clusters are at least the source of this light.
Stars in these globular clusters lack high concentrations of “metals,” a term astronomers use for elements heavier than hydrogen and helium. This suggests to the team that the globules in the Perseus galaxy cluster have made their way in from the large collection of the outer edges of the galaxies, which are also “bad metals”.
Globular clusters comprise the main factor in dwarf galaxies, meaning that some of the intracluster light may come from the remnants of such small galaxies that have been torn apart by tidal forces generated during encounters with larger galaxies.
The team also discovered from the Euclid observation of Perseus that the number of small dwarf galaxies in this galaxy cluster increases as one moves away from the center of the cluster.
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The research helps verify Euclid’s ability to understand the evolution of galaxies and galaxy clusters and, therefore, how the universe looked the way it does to us today.
Interestingly, these results are among the first scientific results from the Euclid Early Release Observations, which do not represent the first 24 hours of Euclid’s observations before he began observing his main scientific targets, the billions of galaxies across more than a third of the sky on 14 February 2024.
The team’s research can be seen on the paper’s arXiv site.
