ESA reveals Euclid’s first five images

by Martijn Luinstra

The European Space Agency (ESA) has released the first full-color images from Euclid, the agency’s latest space telescope designed to study the nature and distribution of dark matter and dark energy in the universe. During a video broadcast on Nov. 7, scientists, engineers, and agency officials unveiled the telescope’s first five images.

The images reveal five targets at different distances, with the furthest, the Perseus Cluster of galaxies, being released first, followed by spiral galaxy IC 342, irregular galaxy NGC 6822, globular cluster NGC 6397, and finally the Horsehead Nebula. These targets were chosen to demonstrate the full potential of Euclid’s two instruments, a visible-wavelength camera called the VISible instrument (VIS) and a near-infrared camera/spectrometer called Near-Infrared Spectrometer and Photometer (NISP).

“The images exceed expectations,” said Euclid NL national project manager Edwin Valentijn of the University of Groningen, The Netherlands, in an interview with NSF. “It is unbelievable how well Euclid meets its specifications!”

However, this success was hardly guaranteed a few months ago when the telescope experienced issues during its commissioning phase. The problems delayed the start of Euclid’s six-year mission by more than a month. With the issues resolved, the telescope can finally begin mapping a third of the sky to study dark matter and dark energy.

Euclid’s commissioning initially began without issues while the telescope was still on its way to Sun-Earth Lagrange point 2 (L2) after lifting off on July 1 atop a SpaceX Falcon 9 rocket from Space Launch Complex 40 in Florida. Problems arose soon after the telescope turned on its detectors for the first time, though.

When Euclid sent back its first images, the team noticed the telescope picked up flares of stray sunlight. “We now know it was caused by a thruster bracket that stuck out past the sun shield and reflected light inwards,” explained Valentijn. “Fortunately, this could be moved outside the focal plane by rolling the telescope by 3 degrees, so it’s gone now.”

A second issue was caused by the Sun, which is currently in a period of high activity. When X-rays from solar flares reach Euclid’s detectors, they interfere with the observations. Luckily, scientists can minimize the impact to less than 1% of the data by simply removing the affected data. Repeating observations at a later moment could potentially negate these issues entirely.

The biggest issue arose when the Fine Guidance Sensor was not able to reliably track guide stars. This meant the telescope was unstable and unable to precisely point at its targets, a crucial requirement for the mission’s science goals. “I was always afraid to hear about this because that would mean we had real problems,” said Valentijn.

After the guidance issues were resolved by uploading a software patch to the telescope, Euclid could finally start making scientific observations. The first of which has now been released to the public.

The Perseus Cluster of galaxies

“My favorite image is the one of the Perseus Cluster,” said Valentijn enthusiastically. “It is hard to see depth in a flat image, but you really can in this one. It shows 1,000 large galaxies that are relatively close by in the cluster, and behind those, you can see 100,000 more galaxies, all the way to the limit of what Euclid can observe, 10 billion years back in time.”

Euclid’s view on the Perseus Cluster of galaxies. (Credit: ESA/Euclid/Euclid Consortium/NASA/J.-C. Cuillandre (CEA Paris-Saclay)/G. Anselmi)

“This is an image that really shows what Euclid is made for and what it can do,” Valentijn continued. “It took just about one hour to take a single image. I cannot stress that enough. We will take 30,000 more of these!”

Located 240 million light-years from Earth, the Perseus Cluster is one of the largest structures in the nearby universe. According to astronomers, dark matter was essential to the formation of this cluster. Euclid’s image shows small, faint galaxies in the cluster that haven’t been visible in other images.

Even the far-away galaxies in the background are of interest to astronomers because their light is distorted, an effect called weak lensing. Scientists can deduce how dark matter is distributed throughout the universe by studying these distortions. Euclid’s wide field of view and high resolution make this study possible by collecting lots of data in a short time.

“How can you even measure distortion if you don’t know the original shape,” Valentijn pondered. “Well, you can’t! You can only do that by applying statistics, which will give better results if you have more data. That is why we want so much data.”

Euclid’s image of the Perseus Cluster can be found here.

Spiral galaxy IC 342

The next image to be released was of a spiral galaxy known as IC 342, nicknamed the Hidden Galaxy. This galaxy owes its nickname to the fact that it is obscured by the Milky Way from our perspective. It is located 11 million light-years from Earth and appears in the sky about as large as the full Moon.

Euclid’s view of spiral galaxy IC 342. (Credit: ESA/Euclid/Euclid Consortium/NASA/J.-C. Cuillandre (CEA Paris-Saclay)/G. Anselmi)

Using infrared instruments, telescopes can look through the Milky Way’s dust and observe IC 342. Earlier infrared information made by NASA’s Hubble Space Telescope previously observed parts of this galaxy, but Euclid’s NISP instrument allowed scientists to see the galaxy in its entirety for the first time.

“This image might look normal, as if every telescope can make such an image, but that is not true,” explained Euclid Consortium scientist Leslie Hunt of the National Institute for Astrophysics in Italy on behalf of a broader team working on showcasing galaxies imaged by 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. 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.”

Euclid’s image of IC 342 can be found here.

Irregular galaxy NGC 6822

The third image released was of an irregular dwarf galaxy called NGC 6822, which is located 1.6 million light years away from Earth. Despite the galaxy having been observed before by many telescopes, including the James Webb Space Telescope and ground-based telescopes, Euclid was able to provide a new view in only one hour.

Euclid’s view of irregular galaxy NGC 6822. (Credit: ESA/Euclid/Euclid Consortium/NASA/J.-C. Cuillandre (CEA Paris-Saclay)/G. Anselmi)

“The Euclid field of view is about 100 times bigger than the one of the James Webb Space Telescope, and that’s unique for Euclid,” said Euclid Consortium deputy lead Francis Bernardeau of the Institut d’Astrophysique de Paris CNRS and CEA Paris-Saclay, France. “Even if you think of ground-based observations you can reach a similar field of view, but the resolution is – by nature – degraded because of the atmospheric turbulence.”

Euclid’s image of NGC 6822 can be found here.

Globular cluster NGC 6397

The fourth image to be released was that of a globular cluster in our own Milky Way. The cluster, called NGC 6397, is located about 7,800 light-years from Earth.

“You can see the entire cluster all at once,” described Valentijn. “There’s a bunch of stars in the middle, but nearly all stars in the image are part of this cluster. It is fantastic to be able to see all of this at the same time!”

Scientists will use Euclid to study clusters in the search for trails of stars called tidal tails. Observing these tails allows scientists to calculate how the clusters orbit the Milky Way. “And this will tell us how dark matter is distributed in the Milky Way,” said Euclid Consortium scientist Davide Massari of the National Institute for Astrophysics in Italy.

Euclid’s view of globular cluster NGC 6397. (Credit: ESA/Euclid/Euclid Consortium/NASA/J.-C. Cuillandre (CEA Paris-Saclay)/G. Anselmi)

“We expect all of the globular clusters in the Milky Way to have them, but so far we have only seen them around just a few,” said Massari. “If there are no tidal tails, then there could be a dark matter halo around the globular cluster, preventing the outer stars from escaping. But we don’t expect dark matter haloes around smaller-scale objects like globular clusters, only around bigger structures like dwarf galaxies or the Milky Way itself.”

Euclid’s image of NGC 6397 can be found here.

The Horsehead Nebula

The final image is a colorful shot of the Horsehead Nebula, also known as Barnard 33. At a distance to Earth of 1,375 light-years, this is the closest object among the five Euclid observed.

This region in the constellation Orion is a so-called stellar nursery, where dust and gas accumulate into stars and planets. Euclid’s images help astronomers find new stars, brown dwarfs, and planet-like objects in this cloud.

“These images contain objects that are almost planet-like, which are very faint and on the boundary between star and planet,” said Valentijn. “These are quite interesting for astronomers, as we suspect there are many more light stars than heavy stars, but we don’t know how many more there are.”

Euclid’s view of Barnard 33, or the Horsehead Nebula. (Credit: ESA/Euclid/Euclid Consortium/NASA/J.-C. Cuillandre (CEA Paris-Saclay)/G. Anselmi)

Like the other images, this view showcases Euclid’s ability to capture a lot of detail in a short time.

“We have never seen astronomical images like this before, containing so much detail,” said René Laureijs, ESA’s Euclid Project Scientist. “They are even more beautiful and sharp than we could have hoped for, showing us many previously unseen features in well-known areas of the nearby Universe. Now we are ready to observe billions of galaxies, and study their evolution over cosmic time.”

Euclid’s image of the Horsehead Nebula can be found here.

Final steps before routine observations

Euclid will start routine observations in early 2024, but before that, the team needs to perform some final fine-tuning of the telescope. During these scheduled operations, the team will characterize the telescope’s optical performance and how the space environment affects the systems through heat and cosmic radiation. After that, the telescope can finally begin collecting vast amounts of data on dark matter and dark energy.

“It will take a while before we’ve collected enough data for a breakthrough,” warns Valentijn. “But Euclid also delivers legacy science, which does not directly involve dark matter or dark energy. We certainly expect interesting discoveries, even in the near future.”

(Lead image: A compilation of the five first images from Euclid. Credit: ESA/Euclid/Euclid Consortium/NASA/J.-C. Cuillandre (CEA Paris-Saclay)/G. Anselmi)

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