Euclid Mission Uncovers 1.5 Trillion Orphan Stars Drifting in Space

Perseus Cluster of Galaxies Euclid Satellite

The image, captured by the Euclid satellite, depicts the Perseus cluster of galaxies bathed in a gentle, soft blue light emanating from orphan stars. These orphan stars are dispersed throughout the cluster, extending up to 2 million light-years from its center. The cluster galaxies stand out as luminous elliptical shapes against the dark expanse of space. Credit: ESA/Euclid/Euclid Consortium/NASA, image processing by M. Montes (IAC) and J.-C. Cuillandre (CEA Paris-Saclay)

Euclid’s first scientific images have revealed over 1.5 trillion orphan stars in the Perseus galaxy cluster, shedding light on their origins and the cluster’s structure.

More than 1,500 billion orphan stars scattered throughout the Perseus cluster of galaxies have been revealed in the first scientific pictures from the Euclid satellite mission.

This discovery, which was led by astronomers from the University of Nottingham, provides new insights into the origins of these celestial wanderers.

Located approximately 240 million light-years from Earth, the Perseus cluster is among the most massive structures in the universe, containing thousands of galaxies. Within this vast expanse, the Euclid satellite detected faint, ghostly lights — the orphan stars — drifting between the galaxies of the cluster.

Orphan Star Surprises

Because stars naturally form within galaxies, the presence of orphan stars outside these structures raised intriguing questions about their origins.

Professor Nina Hatch, who led the project team, said, “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 the intracluster stars came from. By studying their colors, luminosity, and configurations, we found they originated from small galaxies.”

The orphan stars are characterized by their bluish hue and clustered arrangement. Based on these distinctive features the 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.

Unexpected Orbital Patterns

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

Dr. Jesse Golden-Marx, a Nottingham astronomer involved in the study, commented, “This novel observation suggests that the massive Perseus cluster may have recently undergone a merger with another group of galaxies. This recent merger could have induced a gravitational disturbance, causing either the most massive galaxy or the orphan stars to deviate from their expected orbits, thus resulting in the observed misalignment.”

Dr. Matthias Kluge, first author on the study, 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 add it all up, it accounts for about 20% of the luminosity of the entire cluster.”

Euclid’s Mission and Capabilities

Launched on July 1, 2023, the European Space Agency’s Euclid mission is designed to explore the composition and evolution of the dark Universe. The space telescope will create a great map of the large-scale structure of the Universe across space and time by observing billions of galaxies out to 10 billion light-years, across more than a third of the sky. Euclid will explore how the Universe has expanded and how structure has formed over cosmic history, revealing more about the role of gravity and the nature of dark energy and dark matter.

Dr. Mireia Montes, an astronomer from the Institute of Astrophysics on the Canary Islands involved in the study said, “This work was only possible thanks to Euclid’s sensitivity and sharpness.” Euclid’s revolutionary design means that it can take images with similar sharpness as the Hubble Space Telescope, but covering an area that is 175 times larger.

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