Euclid Telescope Spots Over a Trillion Orphaned Stars

For the first time, scientists have discovered a staggering 1.5 trillion orphan stars drifting through a vast galaxy cluster using the Euclid Space Telescope. These wandering stars, torn from their parent galaxies, fill the Perseus cluster with a ghostly blue light.

Chasing the invisible

The Euclid Space Telescope, launched from Cape Canaveral by SpaceX on July 1, 2023, is an ambitious mission of the European Space Agency (ESA) designed to explore the mysteries of the Universe, including dark energy and dark matter. On the one hand, dark energy is a mysterious force that accelerates the expansion of the Universe, while dark matter is an invisible substance that does not interact with light, but makes up a large part of the mass of the cosmos. Euclid’s mission is to map the distribution of these dark components to better understand their influence on the formation and evolution of cosmic structures.

Discovery of orphan stars

In his first observations, Euclid made a stunning discovery: an incredible number of 1.5 billion orphaned stars (1.5 million billion) drifting through the perseus cluster. Located 240 million light-years from Earth, it is one of the largest structures in the Universe. These stars, torn from their original galaxies, float freely in the space between the galaxies of the cluster, creating a ghostly blue light called intra-cluster light. This intra-cluster light is extremely weak (thousands of times darker than Earth’s night sky). However, thanks to his sensitivity and advanced observational capabilities, Euclid managed to detect it and study its properties.

What origins?

By analyzing this light, scientists were able to determine that these orphan stars come mainly from small galaxies disrupted or destroyed by gravitational interactions with larger galaxies of the Perseus cluster. More precisely, some of these stars have been torn from the outskirts of galaxies by tidal forceswhile others come from completely disintegrated dwarf galaxies. Another surprising discovery was that contrary to what one might expect, these orphan stars do not orbit the largest galaxies in the cluster. Instead, they rotate around a point between the two brightest galaxies of the cluster, NGC 1275 and NGC 1272. This observation suggests that the Perseus cluster may have recently merged with another group of galaxies, disrupting the orbits of stars and galaxies.
Illustration of a dwarf galaxy being disrupted by a larger galaxy that is tearing its stars away. Credits: NOIRLab/NSF/AURA/M. Zamani

Implications for understanding galaxy clusters

Euclid’s observations also revealed the presence of 50,000 globular clustersdense spherical collections of tens of thousands to millions of stars, in the Perseus cluster. These globular clusters, which lack metals (elements heavier than hydrogen and helium), appear to originate in the peripheral regions of the cluster’s galaxies. Their distribution suggests that they may be the source of some of the observed intra-cluster light. Note that the findings from Euclid’s early observations represent only the first 24 hours telescope operation. Starting February 14, 2024, Euclid will begin observing its primary science targets: billions of galaxies spread across more than a third of the sky. The data collected will provide insights into the evolution of galaxies and galaxy clusters, and how the Universe came to be what it is today. results obtained so far thus demonstrate the power and potential of Euclid to advance our understanding of the dark Universe and its mysterious components. The orphan stars of the Perseus cluster are thus just the beginning that promises many other fascinating discoveries to come.