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Euclid’s first images: the dazzling edge of darkness

7 November 2023

Today ESA’s Euclid space mission will release its first full-colour images of the cosmos. Never before has a telescope been able to create such razor-sharp astronomical images across such a large patch of the sky, and looking so far into the distant Universe. These five images illustrate Euclid’s full potential; they show that the telescope is ready to create the most extensive 3D map of the Universe yet, to uncover some of its hidden secrets.

Euclid, our dark Universe detective, has a difficult task: to investigate how dark matter and dark energy have made our Universe look like it does today. 95% of our cosmos appears to be made of these mysterious ‘dark’ entities But we don’t understand what they are because their presence causes only very subtle changes in the appearance and motions of the things we can see.

To reveal the ‘dark’ influence on the visible Universe, over the next six years Euclid will observe the shapes, distances and motions of billions of galaxies out to 10 billion light-years. By doing this, it will create the largest cosmic 3D map ever made.

What makes Euclid’s view of the cosmos special is its ability to create a remarkably sharp visible and infrared image across a huge part of the sky in just one sitting.

The images, which will be released today showcase this special capacity: from bright stars to faint galaxies, the observations show the entirety of these celestial objects, while remaining extremely sharp, even when zooming in on distant galaxies.

“Dark matter pulls galaxies together and causes them to spin more rapidly than visible matter alone can account for; dark energy is driving the accelerated expansion of the Universe. Euclid will for the first-time allow cosmologists to study these competing dark mysteries together,” explains ESA Director of Science, Professor Carole Mundell. “Euclid will make a leap in our understanding of the cosmos as a whole, and these exquisite Euclid images show that the mission is ready to help answer one of the greatest mysteries of modern physics.”

“We have never seen astronomical images like this before, containing so much detail. 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,” says René Laureijs, ESA’s Euclid Project Scientist.

“Our high standards for this telescope paid off: that there is so much detail in these images, is all thanks to a special optical design, perfect manufacturing and assembly of telescope and instruments, and extremely accurate pointing and temperature control,” adds Giuseppe Racca, ESA’s Euclid Project Manager.

“I wish to congratulate and thank everyone involved with making this ambitious mission a reality, which is a reflection of European excellence and international collaboration. The first images captured by Euclid are awe-inspiring and remind us of why it is essential that we go to space to learn more about the mysteries of the Universe,” says ESA Director General Josef Aschbacher.

Zoom into the Universe through Euclid’s eyes

The Perseus Cluster of galaxies

This incredible snapshot from Euclid is a revolution for astronomy. The image shows 1000 galaxies belonging to the Perseus Cluster, and more than 100 000 additional galaxies further away in the background.

Many of these faint galaxies were previously unseen. Some of them are so distant that their light has taken 10 billion years to reach us. By mapping the distribution and shapes of these galaxies, cosmologists will be able to find out more about how dark matter shaped the Universe that we see today.

This is the first time that such a large image has allowed us to capture so many Perseus galaxies in such a high level of detail. Perseus is one of the most massive structures known in the Universe, located ‘just’ 240 million light-years away from Earth.

Astronomers demonstrated that galaxy clusters like Perseus can only have formed if dark matter is present in the Universe. Euclid will observe numerous galaxy clusters like Perseus across cosmic time, revealing the ‘dark’ element that holds them together.

Euclid’s view of the Perseus cluster of galaxies. — Euclid’s first images: a view of the Perseus cluster of galaxies. ESA/Euclid/Euclid Consortium/NASA, image processing by J.-C. Cuillandre (CEA Paris-Saclay), G. Anselmi, CC BY-SA 3.0 IGO

Spiral galaxy IC 342

Over its lifetime, our dark Universe detective will image billions of galaxies, revealing the unseen influence that dark matter and dark energy have on them. That’s why it’s fitting that one of the first galaxies that Euclid observed is nicknamed the ‘Hidden Galaxy’, also known as IC 342 or Caldwell 5. Thanks to its infrared view, Euclid has already uncovered crucial information about the stars in this galaxy, which is a look-alike of our Milky Way.

Irregular galaxy NGC 6822

To create a 3D map of the Universe, Euclid will observe the light from galaxies out to 10 billion light-years. Most galaxies in the early Universe don’t look like the quintessential neat spiral, but are irregular and small. They are the building blocks for bigger galaxies like our own, and we can still find some of these galaxies relatively close to us. This first irregular dwarf galaxy that Euclid observed is called NGC 6822 and is located close by, just 1.6 million light-years from Earth.

Globular cluster NGC 6397

This sparkly image shows Euclid’s view on a globular cluster called NGC 6397. This is the second-closest globular cluster to Earth, located about 7800 light-years away. Globular clusters are collections of hundreds of thousands of stars held together by gravity. Currently no other telescope than Euclid can observe an entire globular cluster in one single observation, and at the same time distinguish so many stars in the cluster. These faint stars tell us about the history of the Milky Way and where dark matter is located.

The Horsehead Nebula

Euclid shows us a spectacularly panoramic and detailed view of the Horsehead Nebula, also known as Barnard 33 and part of the constellation Orion. In Euclid’s new observation of this stellar nursery, scientists hope to find many dim and previously unseen Jupiter-mass planets in their celestial infancy, as well as young brown dwarfs and baby stars.

New discoveries, soon

Euclid’s first view of the cosmos is not only beautiful, but also immensely valuable for the scientific community.

Firstly, it showcases that Euclid’s telescope and instruments are performing extremely well and that astronomers can use Euclid to study the distribution of matter in the Universe and its evolution at the largest scales. Combining many observations of this quality covering large areas of the sky will show us the dark and hidden parts of the cosmos.

Secondly, each image individually contains a wealth of new information about the nearby Universe (click on the individual images to learn more about this). “In the coming months, scientists in the Euclid Consortium will analyse these images and publish a series of scientific papers in the journal Astronomy & Astrophysics, together with papers about the scientific objectives of the Euclid mission and the instrument performance,” adds Yannick Mellier, Euclid Consortium lead.

And finally, these images take us beyond the realm of dark matter and dark energy, also showing how Euclid will create a treasure trove of information about the physics of individual stars and galaxies.

Getting ready for routine observations

Euclid launched to the Sun-Earth Lagrange point 2 on a SpaceX Falcon 9 rocket from Cape Canaveral Space Force Station in Florida, USA, at 17:12 CEST on 1 July 2023. In the months after launch, scientists and engineers have been engaged in an intense phase of testing and calibrating Euclid’s scientific instruments. The team is doing the last fine-tuning of the spacecraft before routine science observations begin in early 2024.

Over six years, Euclid will survey one third of the sky with unprecedented accuracy and sensitivity. As the mission progresses, Euclid’s bank of data will be released once per year, and will be available to the global scientific community via the Astronomy Science Archives hosted at ESA’s European Space Astronomy Centre in Spain.

Press release and pictures from ESA Euclid

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Hubble data confirms galaxies lacking dark matter

NGC1052-DF2 Hubble galaxies dark matter — Hubble data confirms galaxies lacking dark matter: NGC1052-DF2. Credits: NASA, ESA, Z. Shen and P. van Dokkum (Yale University), and S. Danieli (Institute for Advanced Study)

The most accurate distance measurement yet of ultra-diffuse galaxy (UDG) NGC1052-DF2 (DF2) confirms beyond any shadow of a doubt that it is lacking in dark matter. The newly measured distance of 22.1 +/-1.2 megaparsecs was obtained by an international team of researchers led by Zili Shen and Pieter van Dokkum of Yale University and Shany Danieli, a NASA Hubble Fellow at the Institute for Advanced Study.

“Determining an accurate distance to DF2 has been key in supporting our earlier results,” stated Danieli. “The new measurement reported in this study has crucial implications for estimating the physical properties of the galaxy, thus confirming its lack of dark matter.”

The results, published in Astrophysical Journal Letters on June 9, 2021, are based on 40 orbits of NASA’s Hubble Space Telescope, with imaging by the Advanced Camera for Surveys and a “tip of the red giant branch” (TRGB) analysis, the gold standard for such refined measurements. In 2019, the team published results measuring the distance to neighboring UDG NGC1052-DF4 (DF4) based on 12 Hubble orbits and TRGB analysis, which provided compelling evidence of missing dark matter. This preferred method expands on the team’s 2018 studies that relied on “surface brightness fluctuations” to gauge distance. Both galaxies were discovered with the Dragonfly Telephoto Array at the New Mexico Skies observatory.

“We went out on a limb with our initial Hubble observations of this galaxy in 2018,” van Dokkum said. “I think people were right to question it because it’s such an unusual result. It would be nice if there were a simple explanation, like a wrong distance. But I think it’s more fun and more interesting if it actually is a weird galaxy.”

In addition to confirming earlier distance findings, the Hubble results indicated that the galaxies were located slightly farther away than previously thought, strengthening the case that they contain little to no dark matter. If DF2 were closer to Earth, as some astronomers claim, it would be intrinsically fainter and less massive, and the galaxy would need dark matter to account for the observed effects of the total mass.

Dark matter is widely considered to be an essential ingredient of galaxies, but this study lends further evidence that its presence may not be inevitable. While dark matter has yet to be directly observed, its gravitational influence is like a glue that holds galaxies together and governs the motion of visible matter. In the case of DF2 and DF4, researchers were able to account for the motion of stars based on stellar mass alone, suggesting a lack or absence of dark matter. Ironically, the detection of galaxies deficient in dark matter will likely help to reveal its puzzling nature and provide new insights into galactic evolution.

While DF2 and DF4 are both comparable in size to the Milky Way galaxy, their total masses are only about one percent of the Milky Way’s mass. These ultra-diffuse galaxies were also found to have a large population of especially luminous globular clusters.

This research has generated a great deal of scholarly interest, as well as energetic debate among proponents of alternative theories to dark matter, such as Modified Newtonian dynamics (MOND). However, with the team’s most recent findings–including the relative distances of the two UDGs to NGC1052–such alternative theories seem less likely. Additionally, there is now little uncertainty in the team’s distance measurements given the use of the TRGB method. Based on fundamental physics, this method depends on the observation of red giant stars that emit a flash after burning through their helium supply that always happens at the same brightness.

“There’s a saying that extraordinary claims require extraordinary evidence, and the new distance measurement strongly supports our previous finding that DF2 is missing dark matter,” stated Shen. “Now it’s time to move beyond the distance debate and focus on how such galaxies came to exist.”

Moving forward, researchers will continue to hunt for more of these oddball galaxies, while considering a number of questions such as: How are UDGs formed? What do they tell us about standard cosmological models? How common are these galaxies, and what other unique properties do they have? It will take uncovering many more dark matter-less galaxies to resolve these mysteries and the ultimate question of what dark matter really is.

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The published ApJL article is available here: https://iopscience.iop.org/article/10.3847/2041-8213/ac0335

A pre-publication is available at: https://arxiv.org/abs/2104.03319

About the Institute

The Institute for Advanced Study is one of the world’s foremost centers for theoretical research and intellectual inquiry. Located in Princeton, N.J., the IAS is dedicated to independent study across the sciences and humanities. Founded in 1930, the Institute is devoted to advancing the frontiers of knowledge without concern for immediate application. From founding IAS Professor Albert Einstein to the foremost thinkers of today, the IAS enables bold, curiosity-driven innovation to enrich society in unexpected ways.

Each year, the Institute welcomes more than 200 of the world’s most promising post-doctoral researchers and scholars who are selected and mentored by a permanent Faculty, each of whom are preeminent leaders in their fields. Among present and past Faculty and Members there have been 35 Nobel Laureates, 42 of the 60 Fields Medalists, and 21 of the 24 Abel Prize Laureates, as well as many MacArthur Fellows and Wolf Prize winners.

Press release from the Institute for Advanced Study

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