The European Space Agency released the first five science images from the Euclid space telescope Tuesday, showing how the wide-angle observatory will survey familiar cosmic wonders like galaxies and stars to study the unseen dark energy and dark matter that dominate the Universe.
Stationed nearly a million miles (1.5 million kilometers) from Earth, Euclid will scan one-third of the sky over the next six years, collecting an estimated 1 million images of billions of galaxies. Scientists have developed sophisticated algorithms to analyze the data coming down from Euclid to measure the distances and shapes of each of these galaxies.
From that, scientists can infer how the influence of dark matter pulls on the galaxies, forming clusters and causing them to spin faster. Dark energy is the mysterious force that is driving the accelerated expansion of the Universe.
It's a novel way of studying something that defies detection with telescopes. If the mission is successful, Euclid won't become famous for producing pretty pictures like the larger Hubble or Webb telescopes, but it could rewrite astronomy textbooks if it makes fundamental discoveries about the makeup of the Universe.
Still, the pictures are breathtaking.
“What these images tell us is that the instruments of Euclid are working fantastically, that we are getting ready to start with the ultimate goal of Euclid," said Guadalupe Cañas Herrera, a space science research fellow at ESA.
Using light to see the dark
Euclid's 3.9-foot (1.2-meter) telescope is half the size of Hubble's primary mirror and five times smaller than that of Webb. The secret sauce of the $1.5 billion Euclid mission is its ability to view the Universe with a wide field of view. For example, one of Euclid's first science images shows the Horsehead Nebula, a star-forming region in the constellation Orion about 1,375 light-years from Earth. Many telescopes have observed this nebula before, but Euclid captured a wide, but still sharp, view of the Horsehead Nebula in about one hour.
“We could make this up with other images from other telescopes, but it would take us an awfully long time to take an awful lot of observations and stitch them all together," said Carole Mundell, ESA's director of science.
Scientists say it would take Hubble hundreds of years to complete the same extra-galactic survey as the one planned for Euclid, which will cover in a week the same area of sky that Hubble has observed in its 33-year mission. The objective is for Euclid to gather enough data for a statistical survey of galaxies to improve astronomers' understanding of dark energy and dark matter, which are thought to make up about 95 percent of the Universe. The rest of the cosmos is made of regular atoms and molecules that we can see and touch.
“If you want to observe the Universe in a cosmological way, you don’t want to be restricted to particular areas,” Giuseppe Racca, ESA’s Euclid project manager, said before Euclid's launch. “You really want to observe a lot.”
Built in Europe, Euclid launched on July 1 from Cape Canaveral, Florida, aboard a SpaceX Falcon 9 rocket and reached its observing orbit in deep space about a month later. Since then, ground controllers have carefully calibrated the observatory's two instruments—a 600-megapixel visible light camera and a 64-megapixel near-infrared spectrograph and photometer.
Engineers discovered a relatively minor issue with sunlight reflecting off a bracket back toward Euclid's visible camera, but it's only an issue at certain viewing angles. Mission planners have redesigned Euclid's sky survey—due to begin early next year—to avoid pointing the telescope at these problematic angles, which could have minor impacts on the mission's observing efficiency but not on data quality.
Another image from Euclid contains a collection of cosmic wonders, showing the Perseus Cluster, a grouping of thousands of galaxies some 240 million light-years away. In the background, the image contains more than 100,000 additional faint galaxies as far away as 10 billion light-years, most of which were previously undetected. In a press statement accompanying Tuesday's image release, ESA called this image a "revolution for astronomy."
Jean-Charles Cuillandre, a Euclid scientist and expert in wide-field ultra-deep imaging, said the Perseus Cluster could only have formed in the presence of dark matter. Galaxy clusters condense at the crossroads of filaments of dark matter that pull together massive galaxies over billions of years.
Euclid has also observed a galaxy that is obscured by the bright foreground of the main disk of our own Milky Way. This spiral galaxy, named IC 342 and sometimes called the "Hidden Galaxy," appears similar to what we might see if we could see our own galaxy from the outside. Hubble has previously imaged the core of the Hidden Galaxy, but Euclid takes a wider view, as seen in the image at the top of this page.
“This is the first telescope which can capture in one single exposure the entire galaxy and the surroundings with this exquisite resolution, so you have very sharp images," said Francis Bernardeau, deputy lead of the consortium of scientists ready to analyze data from Euclid.
"What’s so special here is that we have a wide view covering the entire galaxy, but we can also zoom in to distinguish single stars and star clusters," said Leslie Hunt, a scientist in the Euclid consortium, in an ESA press release. "This makes it possible to trace the history of star formation and better understand how stars formed and evolved over the lifetime of the galaxy.”
