The European Space Agency (ESA) has today published the first images obtained by Euclid, an ambitious mission whose main objective is to create the most precise and extensive three-dimensional map of the universe to date to study two of the most mysterious components of the cosmos. : dark matter and energy.
The so-called dark energy is the engine that causes the accelerated expansion of the universe and whose nature and properties are unknown. For its part, it is known that the cosmos contains a type of matter, called dark because it does not emit light, that it is not composed of atoms and that, in addition, it dominates in a proportion of 6 to 1 over ordinary matter (which forms everything). that we see in the universe, such as stars and planets). Together, dark energy and matter represent more than 95% of the content of the cosmos.
Since it was launched into space on July 1 of this year, Euclid has traveled toward its destination, a place in space known as the L2 Lagrange point. Located 1.5 million kilometers from Earth in the opposite direction to the Sun, this location is especially stable thanks to the combined action of the gravity of our planet and the Sun. It is the same region in which the James Webb Space Telescope works. .
Euclid's first five photographs demonstrate the capabilities of its instruments (a telescope, equipped with a 1.2 meter diameter mirror, a 600 megapixel camera and an infrared sensor). The combination of this equipment makes it possible to analyze information from very distant objects, but what distinguishes Euclid from other space telescopes is that it can capture, in a single observation, images of very large regions of the sky.
The satisfaction of the team of scientists that make up the Euclid consortium with these first results was evident in the press conference that accompanied the publication of the photographs. In the words of Josef Aschbacher, Director General of ESA, “the first images captured by Euclid are impressive and remind us why it is essential that we go to space to learn more about the mysteries of the Universe.”
Euclid's unique capabilities are evident in the photograph taken of the Perseus galaxy cluster, a huge group located 240 million light-years away. According to those responsible for the mission, 1,000 galaxies belonging to this cluster appear in the image and more than 100,000 additional galaxies much more distant, located in the background and that have never been observed until now.
These smaller, more distant galaxies are of special interest to the project. As highlighted by Jean-Charles Cuillandre, a scientist with the Euclid consortium at the CEA Paris-Saclay center (France), the mission will allow us to verify one of the predictions derived from theoretical models of the universe, according to which the cosmos should contain many more dwarf galaxies than have been found to date.
In addition, the study of distant galaxies (the light from some of them left their origin 10 billion years ago) is one of the main tools that Euclid will use to study dark energy and matter. Indeed, the light we receive from these objects will have been distorted when, to reach our instruments, it has had to pass through regions in which a lot of mass is concentrated. As a consequence, galaxies will appear very slightly deformed, an effect called weak gravitational lensing that will reveal the presence of dark matter along the path traveled by light.
However, the distortions caused by weak gravitational lensing are so subtle that it will only be possible to use them through a complete statistical study involving hundreds of millions of galaxies. For this reason, Euclid was designed to be able to observe, at once and with great precision, large areas of the sky. Thus, in the photograph of the Perseus cluster, ESA estimates that more than 50,000 candidate galaxies appear to have suffered distortions. When the mission ends, Euclid will have observed a region of the sky equivalent to 30,000 times that contained in this image.
The faint light that is observed in this photograph and that occupies the space between the most important components of the cluster is also interesting for astronomers, since it is the result of the radiation of a multitude of stars expelled from their galaxies due to the gravitational interactions between them. Its analysis can tell the history of the cluster and also show how dark matter is distributed inside it.
Another of Euclid's images shows the galaxy IC 342, a stellar city that could be similar to the Milky Way. Despite being located in our galactic neighborhood, only 11 million light-years away, observing it is very complex because the disk of our own galaxy intervenes in the line of sight. For this reason, IC 342 is nicknamed the hidden galaxy.
To obtain the photograph, Euclid has used its observation capacity in the near infrared, a wavelength capable of passing through the galactic dust found in the path.
The galaxy NGC 6822 is another of the protagonists of the first installment of Euclid images. It is an irregular galaxy with low metallic content, a term used in astronomy to refer to any chemical element heavier than hydrogen and helium.
Since the most complex chemical elements have been formed by previous generations of stars (which have forged this material through nuclear fusion and released it into space at the time of their death), the presence of metals in a galaxy is indicative of his age. Therefore, objects like NGC 6822 allow us to study how galaxies have evolved during the history of the universe.
The photograph of NGC 6822 was obtained with just one hour of observation, a feat that, according to those responsible for the mission, is impossible to achieve with telescopes located on the surface of our planet. Furthermore, the most powerful space telescopes, such as the James Webb, cannot image such large areas of the sky.
Euclid will observe billions of galaxies like IC 342 or NGC 6822, but much more distant, in order to generate a 3-dimensional map that reveals the so-called cosmic filaments. These are immense structures formed mainly by the accumulation of dark matter and that have acted, throughout the history of the universe, as molds in which galaxies have been grouped, especially at the intersections between these invisible filaments.
The so-called globular clusters contain hundreds of thousands of stars associated by gravity and forming spherical structures. They are found in the outermost areas of galaxies and are believed to be very old objects. Euclid has portrayed one of these clusters, NGC 6397, the second closest to Earth (7,800 light-years away).
From the observation of globular clusters in the Milky Way, the mission hopes to detect flows of stars ejected from these objects due to the gravitational interaction they have suffered with our galaxy. The light from these filaments is very weak and, furthermore, the brightness of the cluster itself makes it difficult to detect. The point is that its study can help trace the orbital movement that the clusters have followed around the Milky Way and, in this way, visualize the distribution of the dark matter that our galaxy contains.
As Davide Massari, from the National Institute of Astrophysics in Italy and member of the Euclid consortium, highlights, “there is currently no other telescope that can observe a globular cluster and at the same time distinguish its most external and weakest components.” Additionally, some of the most capable instruments, such as the Hubble Space Telescope, would require extensive observing time to accomplish what Euclid can complete in just one hour.
The fifth Euclid image has been reserved for one of the most photographed and iconic celestial objects: the Barnard 33 nebula, also known as the Horsehead. It is a birthplace of stars just 1,375 light-years from Earth.
According to Eduardo Martín Guerrero de Escalante, from the Institute of Astrophysics of the Canary Islands in Tenerife, this region is very interesting because the formation of new stars occurs under special circumstances: the influence of the intense ultraviolet radiation of the star Sigma Orionis (located in the upper part of the nebula and which does not appear in the image since its powerful light would prevent details from being appreciated).
In this type of capture, astronomers hope to discover a large number of objects, such as exoplanets with a mass similar to Jupiter and in their initial stages of formation, as well as young stars and also brown dwarfs (bodies much more massive than planets but not enough to start the nuclear fusion processes inside that are typical of stars).
These first images are just a preview of what to expect from the mission. In fact, the first partial data from Euclid is expected to be available in 2025, with a more complete delivery expected in 2027. The main phase of the mission will end in 2030.
Scientists will use the data collected by Euclid to test, using complex computer programs, different theoretical models about energy and dark matter and thus be able to understand their nature and distribution.
ESA estimates that Euclid will generate about 850 gigabytes of data per day (one gigabyte is equivalent to 1.24 million characters), a volume that will certainly require advanced storage and processing processes. Like those existing in the “Port d'Informació Cientifica” of the Autonomous University of Barcelona, one of the computing centers participating in the project.
On the other hand, and beyond the study of dark energy and matter, the gigantic volume of data that Euclid will generate will allow, for decades, countless research to be carried out in the field of astrophysics and cosmology.
The Euclid project has an important participation of Spanish research centers, such as the Institute of Space Sciences (ICE-CSIC), the Institute of High Energy Physics (IFAE), the Institute of Space Studies of Catalonia (IEEC) , the Polytechnic University of Cartagena and the Instituto de Astrofísica de Canarias (IAC).
