The European Space Agency’s (ESA) dark matter probe, Euclid, continues to astonish astronomers with its groundbreaking discoveries. Recently, Euclid detected trillions of orphan stars within one of the largest known celestial clusters, shedding new light on the enigmatic regions of space. This discovery, documented in research published on arXiv, provides critical insights into the Perseus cluster, which is as massive as 650 trillion suns and located millions of light-years away.
Intracluster Stars and Faint Light
These orphan stars are situated outside their original galaxies, occupying the dark, vast spaces—called intraclusters—between galaxies within the Perseus cluster. Despite the darkness of these regions, Euclid detected faint light emitted by these intracluster stars. Scientists are now investigating the origins of this faint light and the orphan stars with Euclid’s advanced observational capabilities.
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Nina Hatch, team leader and a scientist at the University of Nottingham, expressed her amazement at Euclid’s capability: “We were surprised by our ability to see so far into the outer regions of the cluster and discern the subtle colours of this light.” This light, once fully understood, could help map dark matter by revealing the origins of these intracluster stars, which appear to have come from small galaxies.
Orphan Stars in the Perseus Cluster
Using Euclid, scientists discovered approximately 1.5 trillion orphan stars drifting through the Perseus cluster, one of the largest structures in the universe. These stars, which were torn from their home galaxies, fill the intergalactic space with a ghostly blue light. This intracluster light is extremely faint—thousands of times darker than the night sky on Earth—yet it provides crucial information about the composition and dynamics of galaxy clusters.
Matthias Kluge from the Max-Planck Institute for Extraterrestrial Physics highlighted the significance of this light: “This diffuse light is more than 100,000 times fainter than the darkest night sky on Earth. But it is spread over such a large volume that when we add it all up, it accounts for about 20% of the luminosity of the entire cluster.”
Understanding Dark Matter and Galaxy Evolution
Euclid’s observations are pivotal in the study of dark matter and galaxy evolution. The orphan stars, characterized by their blue hue and loose clustering, help trace their origins to smaller galaxies that have been disrupted. Surprisingly, these stars do not orbit the largest galaxies in the Perseus cluster but rather a point between the cluster’s two brightest galaxies, NGC 1275 and NGC 1272. This unexpected finding suggests a recent merger in the Perseus cluster, potentially causing gravitational disturbances that altered the stars’ expected orbits.
In addition to orphan stars, Euclid identified around 50,000 globular clusters within the Perseus cluster. These clusters, dense with stars but low in metal content, indicate they originated from the outer edges of the cluster, further supporting the theory of disrupted dwarf galaxies contributing to the intracluster light.
New Era of Cosmic Exploration
Launched on July 1, 2023, atop a SpaceX Falcon 9 rocket, Euclid’s primary mission is to study dark matter and dark energy. Despite its focus on the “dark universe,” Euclid has proven capable of capturing light from distant galaxies, helping scientists map out the structure and evolution of the cosmos.
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Dr. Michelle Collins, a member of the Euclid team, remarked on the telescope’s potential: “These stunning first images are just the tip of the iceberg. This telescope can reveal millions of new objects in a single day. We’re only just beginning to realise its potential.”