The Euclid satellite’s first scientific images have unveiled over 1.5 trillion orphan stars scattered throughout the Perseus galaxy cluster. This discovery, led by astronomers from the University of Nottingham, sheds new light on the origins of these wandering celestial bodies.

Located 240 million light-years from Earth, the Perseus cluster is one of the most massive structures in the universe, containing thousands of galaxies. However, within this cosmic ensemble, the Euclid satellite captured a faint ghostly light—known as orphan stars—drifting between the galaxies of the cluster.

Stars typically form naturally within galaxies, so the presence of orphan stars outside these structures raises intriguing questions about their origins. Professor Nina Hatch, who led the project team, stated, We were surprised by our ability to see so far into the outer regions of the cluster and discern the subtle colors of this light. This light can help us map dark matter if we understand where intracluster stars come from. By studying their colors, brightness, and configurations, we discovered they originate from small galaxies.

Orphan stars are characterized by their bluish hue and clustered arrangement. Based on these distinctive features, astronomers involved in the study suggest that the stars were torn from the outskirts of galaxies and from the complete disruption of smaller cluster galaxies known as dwarfs.

After being stripped from their parent galaxies, orphan stars were expected to orbit around the largest galaxy in the cluster. However, this study revealed a surprising finding: the orphan stars instead orbit a point located between the two most luminous galaxies in the cluster.

Dr. Jesse Golden-Marx, an astronomer from Nottingham who participated in the study, remarked, This novel observation suggests that the massive Perseus cluster may have recently merged with another group of galaxies. This recent merger could have induced a gravitational disturbance, causing the most massive galaxy or the orphan stars to deviate from their expected orbits, leading to the observed misalignment.

Dr. Matthias Kluge, the study’s first author from the Max Planck Institute for Extraterrestrial Physics in Munich, Germany, stated, 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 sum it all up, it represents about 20% of the luminosity of the entire cluster.

The Euclid mission, led by the European Space Agency (ESA), is designed to explore the composition and evolution of the dark universe. The space telescope will create a vast map of the large-scale structure of the universe across space and time by observing billions of galaxies up to 10 billion light-years away, covering more than a third of the sky. Euclid will explore how the universe has expanded and how its structure has formed throughout cosmic history, revealing more information about the role of gravity and the nature of dark energy and dark matter.

Dr. Mireia Montes, an astronomer from the Institute of Astrophysics of the Canary Islands who participated in the study, declared, This work has only been possible thanks to the sensitivity and sharpness of Euclid. The revolutionary design of Euclid allows it to take images with a sharpness similar to that of the Hubble Space Telescope but covering an area 175 times larger.

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