At first glance, the image doesn’t look like much: a few small bright yellow stars among fainter white stars. And in the middle a spot that looks like a collection of stars.
But zooming in reveals a completely different story. That spot does not consist of stars at all, but of dozens and dozens of galaxies.
This is just one of the images released by the European Space Agency, the early release observations from their Euclid space mission.
For six years, Euclid – launched in July 2023 – will investigate dark matter and dark energy, two invisible elements that make up most of our universe. During that time it will observe billions of galaxies.
Abell 2390 is a cluster of galaxies, a gigantic conglomeration of many galaxies such as the Milky Way. More than 50,000 galaxies can be seen here. (ESA/Euclid/Euclid Consortium/NASA, image processing by J.-C. Cuillandre [CEA Paris-Saclay]G. Anselmi)
This is a close-up of the cluster of galaxies seen in Euclid’s image release from Abell 2390. (ESA/Euclid/Euclid Consortium/NASA, image processing by J.-C. Cuillandre [CEA Paris-Saclay]G.Anselmi)
While these images – five in total – are exciting for astronomers, they are eagerly awaiting what lies ahead.
“This [images] are like pointing to known individual objects of interest,” says Will Percival, director of the Center for Astrophysics at the University of Waterloo, and one of the key science coordinators for the Euclid mission.
“We’ve done some great science with it. But we’re going to do this everywhere; we’re going to survey 50,000 square degrees, a third of the area we could possibly observe. So this is like the known known – the known. objects in the universe. And it’s the unknown unknowns that excite me.”
Here Euclid captures NGC 6744, one of the largest spiral galaxies outside our local patch of space. It is a typical example of the type of galaxy that currently forms most of the stars in the nearby universe. (ESA/Euclid/Euclid Consortium/NASA, image processing by J.-C. Cuillandre [CEA Paris-Saclay]G.Anselmi)
Unlike the Hubble Space Telescope and the James Webb Space Telescope (JWST), Euclid can survey large parts of the sky at once. Even though it has been active for less than a year, it has covered more of the sky than any of the other telescopes.
“Hubble and JWST are fantastic telescopes, but you are looking through a keyhole, so to speak,” said Mike Hudson, a professor at the University of Waterloo who is also part of the Euclid mission. “Now you have a very open window.”
Understanding our universe
What we see makes up only about five percent of the universe. The rest consists of dark matter (about 25 percent) and dark energy (about 70 percent), neither of which we can see. But we know both exist by the way they interact with other matter in our universe.
The Dorado Group of galaxies is one of the richest groups of galaxies in the Southern Hemisphere. Here Euclid records signs of galaxies evolving and merging. (ESA/Euclid/Euclid Consortium/NASA, image processing by J.-C. Cuillandre [CEA Paris-Saclay]G.Anselmi)
Dark matter has mass, and we can “see” it by interacting with galaxy clusters, where it bends light from the galaxies behind it, creating streaks of light, as seen in the close-up of Euclid’s image of Abell 2390.
Dark energy is also invisible, but it is causing our universe to expand faster than ever thought.
“[Euclid’s] The goal is to basically understand what is dark matter? What is dark energy? So it’s designed to really answer two of the big questions that we have right now in physics and cosmology,” Percival said.
“In cosmology we have a standard model called the lambda CDM model – the lambda model for cold dark matter – and it explains very well, virtually everything we see. But we don’t understand the actual components in the model.”
The researchers say they hope Euclid will change that during its six-year mission.
This image shows the galaxy cluster Abell 2764 (top right), a very dense region of space with hundreds of galaxies orbiting in a halo of dark matter. Euclid captures a range of objects in this patch of sky, including many background galaxies, more distant clusters of galaxies, interacting galaxies that have thrown out streams and shells of stars, and a beautiful spiral at the edge that allows us to see the ‘thinness ‘ to see. from his disk. (ESA/Euclid/Euclid Consortium/NASA, image processing by J.-C. Cuillandre [CEA Paris-Saclay]G. Anselmi)
“Euclids will produce the largest and also the best in the sense of highest resolution, the least noisy map of dark matter ever created. It will cover a third of the sky,” Hudson said.
“And furthermore, in addition to covering this huge area of the sky, by studying these background galaxies at different distances from us, we can actually build a three-dimensional map of the dark matter.”
They will use the telescope to look back in time, because it takes billions of years for light from distant galaxies to reach us. Using Euclid, they will look at dark matter from when the universe was much younger and compare it to what it was like in later times, or even as it is today.
Both Percival and Hudson eagerly await what the upcoming sky survey will reveal.
“Because it’s an aerial survey,” Hudson said. “It will also open up enormous possibilities to discover all kinds of individually interesting new things about the universe that we didn’t expect.”
You can learn more about the Euclid mission by visiting the European Space Agency website.