Using the Euclid Space Telescope, scientists have discovered a staggering 1.5 trillion orphan stars drifting through a massive cluster of thousands of galaxies, one of the largest structures in the cosmos.
These orphan stars, torn from their own galaxies, fill the space between the galaxies of the Perseus cluster with a ghostly blue light. This so-called “intra-cluster” light is so faint that it is thousands of times darker than the night sky above Earth.
By observing this intra-cluster light in the Perseus Cluster, located 240 million light-years from Earth and whose mass is equivalent to about 650 trillion suns, Euclid could help scientists better understand where comes the weak luminous component of galaxy clusters and the origins of the cosmic orphans who emit it.
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Euclid was launched from Cape Canaveral in Florida atop a SpaceX Falcon 9 rocket on July 1, 2023. Euclid’s primary mission is to study dark energy, the mysterious force that is accelerating the expansion of the universe , and dark matter, an “invisible” substance that does not work. It does not interact with light and is not made up of atoms like the “everyday” elements that surround us.
However, although it was designed to observe the invisible “dark universe”, the telescope was also capable of detecting light emanating from between the galaxies of the Perseus cluster.
“We were surprised by our ability to see this far into the outer regions of the cluster and discern the subtle colors of this light,” team leader and University of Nottingham scientist Nina Hatch said in a statement. “This light can help us map dark matter if we understand where intra-cluster stars come from. By studying their colors, brightness and configurations, we discovered that they come from small galaxies.”
Orphan stars have the blues
The key to understanding the Perseus orphan stars was Euclid’s ability to see the faintest light in the cluster, the intra-cluster light, which comes not from its galaxies but from among them.
“This diffuse light is more than 100,000 times fainter than the darkest night sky on Earth,” said team member Matthias Kluge of the Max Planck Institute for Extraterrestrial Physics. “But it is distributed over such a large volume that when you add it all up, it represents about 20% of the luminosity of the entire cluster.”
The orphan stars seen by Euclid in the Perseus Cluster are distinguished by their characteristic blue coloring and loose clustering. These characteristics allowed Hatch and his colleagues to trace their origins.
The team determined that some of these stars wandering in intra-cluster space were being pulled away from the outskirts of galaxies via interactions with other galaxies. Other orphan stars they found came from smaller dwarf galaxies in the Perseus Cluster that were completely disrupted.
What the team discovered next surprised them. Once torn from their galaxies of origin, intra-cluster stars should begin to orbit the larger galaxies of the cluster in which they find themselves isolated, almost like a child lost in a shopping mall gravitating towards the adult the closer.
Hatch and his colleagues, however, did not find this in Perseus with Euclid. Instead, they saw that orphan stars were orbiting a point between the cluster’s two brightest galaxies, NGC 1275 and NGC 1272.
“This new observation suggests that the massive Perseus cluster may have recently merged with another group of galaxies,” said team member Jesse Golden-Marx, an astronomer from the University of Nottingham. “This recent merger could have caused a gravitational disturbance, causing the more massive galaxy or orphan stars to deviate from their expected orbits, thus leading to the observed misalignment.”
The same researchers also used Euclid’s sensitive visible-light capabilities to spot 50,000 spherical, densely populated free-flying collections of tens of thousands to millions of stars called “globular clusters” in the Perseus galaxy cluster . Intra-cluster diffuse light appears to be distributed similarly to Perseus’ globular clusters, so these conglomerates of stars 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 implies to the team that globular clusters in the Perseus Cluster have made their way inward from the vast collection of galaxies’ outer edges, which are also “metal-poor.”
Globular clusters are a dominant factor in dwarf galaxies, meaning that some of the intra-cluster light may come from the remnants of these smaller galaxies that have been torn apart by tidal forces generated during encounters with larger galaxies. massive.
The team also discovered, thanks to Euclid’s observation of Perseus, that the number of small dwarf galaxies in this galactic cluster increases as one moves away from the center of the cluster.
The research verifies Euclid’s ability to understand the evolution of galaxies and galaxy clusters and, therefore, how the universe became what it is today.
Interestingly, these findings are among the first scientific results from Euclid’s first observations, representing only the first 24 hours of Euclid’s observations before he began observing his primary scientific targets, billions of galaxies spread over more than a third of the sky on February 14, 2024. .
The team’s research is presented on the document repository site arXiv.