Scientists using the Euclid space telescope have discovered a staggering 1.5 trillion orphan stars drifting within a massive cluster of thousands of galaxies, one of the largest structures in the universe.
Torn away from their home galaxy, these orphan stars fill the space between the Perseus cluster’s galaxies with ghostly blue light. This so-called “intra-cluster” 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 from Earth and has a mass equivalent to about 650 trillion suns, Euclid can help scientists better understand where the faint light component from galaxy clusters comes from and the formation of stars. the origins of the cosmic orphans who spread it.
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Euclid launched on July 1, 2023, atop a SpaceX Falcon 9 rocket from Cape Canaveral, Florida. Euclid’s primary mission is to investigate dark energy, the mysterious force accelerating the expansion of the universe, and dark matter, an “invisible” substance in the universe that does not expand. It does not interact with light and is not composed of atoms like the “everyday” things that surround us.
But although it was designed to look into the invisible “dark universe”, the telescope was also able to detect light emitted between galaxies in the Perseus galaxy cluster.
“We were surprised that we were able 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. said. “This light could help us map dark matter if we understand where stars within clusters come from. By studying their colour, brightness and configuration, we found that they originate from small galaxies.”
Orphan stars have sadness
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 from between galaxies rather than within them.
“This scattered light is 100,000 times fainter than the darkest night sky on Earth,” said Matthias Kluge, team member and Max-Planck Institute for Extraterrestrial Physics. “But it is spread over such a large volume that, when we add it all together, it accounts for about 20% of the brightness of the entire cluster.”
The orphan stars that Euclid saw in the Perseus cluster can be distinguished by their characteristic blue color and loose clusters. These features allowed Hatch and his colleagues to trace their origins.
The team determined that some of these stars floating freely in intra-cluster space were drifted away from the outskirts of galaxies through interactions with other galaxies. The other orphan stars they found came from smaller, completely fragmented dwarf galaxies in the Perseus Cluster.
What the team discovered next surprised them. Once ripped away from their home galaxy, intracluster stars are expected to begin orbiting around the largest galaxies in the cluster where they find themselves isolated, much like a child lost in the mall heads towards the nearest adult.
But Hatch and his colleagues did not find this in Perseus and Euclid. Instead, they found the orphan stars orbiting a spot between NGC 1275 and NGC 1272, the cluster’s two brightest galaxies.
“This new observation suggests that the large Perseus cluster may have recently undergone a merger with another group of galaxies,” said team member and University of Nottingham astronomer Jesse Golden-Marx. “This recent merger may have caused a gravitational perturbation that caused the largest galaxy or orphan stars to deviate from their expected orbits, thus causing the observed misalignment.”
The same researchers also used Euclid’s sensitive visible-light capabilities to detect 50,000 densely packed, spherically free-flying collections of tens of thousands to millions of stars called “globular clusters” in the Perseus galaxy cluster. Intra-cluster scattered light appears to be dispersed in a manner similar to the globular clusters in Perseus; So these star clusters appear to be the source of at least some 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 hints to the team that globular clusters in the Perseus galaxy cluster are pushing inwards from the outer edges of the large collection of galaxies, which are also “metal-poor”.
Globular clusters form a dominant factor in dwarf galaxies; This means that some of the intra-cluster light may originate from the remnants of such smaller galaxies being torn apart by tidal forces generated during encounters with larger galaxies.
The team also discovered from the Euclidean observation of Perseus that the number of small dwarf galaxies in this galactic cluster increases with distance from the center of the cluster.
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The research helps confirm Euclid’s ability to understand the evolution of galaxies and galaxy clusters, and thus how the universe came to look the way it does to us today.
Excitingly, these findings are among the first scientific results from Euclid’s Early Release Observations and represent the first 24 hours of observations before Euclid begins observing its main scientific targets, which include billions of galaxies across more than a third of the sky, on February 14, 2024. .
The team’s research is available on the article repository site arXiv.