A new image from ESA’s Euclid telescope shows approximately 1,000 galaxies belonging to the Perseus cluster — a cluster of galaxies 240 million light-years away in the constellation of Perseus — and more than 100,000 additional galaxies further away in the background.
This image from ESA’s Euclid spacecraft shows the Perseus galaxy cluster. Image credit: ESA / Euclid / Euclid Consortium / NASA / J.-C. Cuillandre, CEA Paris-Saclay / G. Anselmi / CC BY-SA 3.0 IGO.
Approximately 11 million light-years across and located 240 million light-years away, the Perseus cluster is named for its host constellation.
Also known as Abell 426, it is one of the most massive objects in the observable Universe, containing over 1,000 galaxies immersed in a vast gas cloud.
Like all galaxy clusters, most of its observable matter takes the form of a pervasive gas averaging tens of millions of degrees, so hot it only glows in X-rays.
The galaxy sitting in the center of the Perseus cluster is NGC 1275, a very peculiar galaxy that emits abundant radio signals, for this known as Perseus A.
The cluster also hosts several other radio galaxies with complex structure, including NGC 1265, NGC 1272, CR 15, and IC 310.
“Perseus is one of the most massive structures known in the Universe, located ‘just’ 240 million light-years away from Earth, containing thousands of galaxies, immersed in a vast cloud of hot gas,” Euclid Consortium scientists said.
“Astronomers demonstrated that galaxy clusters like Perseus can only have formed if dark matter is present in the Universe.”
“If no dark matter existed, galaxies would be distributed evenly throughout the Universe,” said Euclid Consortium scientist Dr. Jean-Charles Cuillandre, an astronomer at CEA Paris-Saclay.
“Gravity causes dark matter to form filamentary structures often referred to as the cosmic web.”
“The crossing points between dark matter filaments cause galaxies to stick close together, creating a cluster.”
“The cosmic web permeates the whole Universe, and similar structures are seen way beyond Perseus, as far as 12 million light-years away.”
Many galaxies in this cluster are already known, but Dr. Jean-Charles and his colleagues are interested in the tiny galaxies that were not visible in images from other telescopes.
“We want to see the extremely faint and small galaxies, called dwarf galaxies,” Dr. Jean-Charles said.
“They are dominated by older stars that shine in infrared light.”
“According to cosmological simulations, the Universe should contain many more dwarf galaxies than we have found so far.”
“With Euclid, we will be able to see them, if they indeed exist in such a large number as predicted.”
In the image, released this week by the Euclid team, we see over 100,000 galaxies beyond the Perseus cluster, of which over 50,000 can be used to study weak lensing.
“Euclid’s entire sky survey will be 30,000 times larger than this image, resulting in billions of galaxies being imaged,” the astronomers said.
“Another important feature in Euclid’s image of Perseus is the faint light between galaxies in the core of the cluster.”
“This light is caused by free floating stars, a consequence of galaxies interacting with each other.”
“By studying this intracluster light, we can trace back the history of the cluster. It also shows how dark matter is distributed.”
