If the atmospheric conditions allow it, next July 1 at 5:11 p.m. (official time in Spain) the mission that can provide answers to some of the most fundamental questions about our universe will be launched into space.
Why is the cosmos expanding? What is your final destination? What is the nature of the mysterious energy and dark matter that make up 95% of the universe? Do we correctly understand how gravity works on a large scale?
The Euclid mission of the European Space Agency (ESA) will observe, for 6 years, more than 1,500 million galaxies, to build a very detailed map that allows us to see how the great structures of the universe have evolved and how the distribution of matter has varied over time. throughout the last 10 billion years of the history of the cosmos.
The objective is to understand what it is and how the mysterious energy that is accelerating the expansion of the universe (so-called dark energy) behaves, and what is the nature of dark matter, a component that dominates in a ratio of 6 to 1 over matter. ordinary made of atoms. Overall, we estimate that these two components, energy and dark matter, represent more than 95% of the content of the cosmos (the remaining 5% being ordinary matter, that is, stars, galaxies, planets and everything we see around us). .
The concept of dark energy was introduced at the end of the 20th century, when it was discovered, with great surprise, that space is expanding at an ever-increasing rate and that, therefore, there must be a force responsible for this acceleration. However, attempts to explain what this energy is have always been unsuccessful, and its understanding currently represents one of the greatest challenges facing science.
For its part, the existence of dark matter was deduced for the first time in the 1930s from the behavior of galaxies, and since then its presence in the universe has been confirmed by numerous studies and observations. It is an unknown type of matter that does not emit light (hence the name dark) but is subject to the action of gravity. So far, the experiments that have been carried out in particle accelerators have not been able to find it, and we still do not know its true nature.
The Euclid spacecraft is much more than a space telescope. Its main instruments are a mirror 1.2 meters in diameter, a 600-megapixel camera capable of photographing, in a single shot and with a very high level of detail, an area of the sky larger than two full moons, and an infrared sensor. that can break down and analyze light from very distant objects.
With its ability to observe large regions of the sky, Euclid will repeatedly scrutinize 36% of our firmament, which corresponds to the areas that are not obstructed by the projection of our own galaxy and by interplanetary dust that is distributed within the Solar System.
Euclid will operate from a point in space known as Lagrange L2, located 1.5 million km away in the opposite direction from the Sun. It is an especially stable place thanks to the combined action of Earth's gravity and the Sun, and on it is also the James Webb Space Telescope.
The ship will protect its delicate instruments from the incidence of sunlight by means of a large shield, since it is necessary for the infrared sensors to operate at a temperature not exceeding -180C, to prevent the instrumental heat itself from interfering with the observations.
In order to achieve his ambitious goals, Euclid will combine two complementary detection methods to obtain highly accurate maps of the structure of the universe and its evolution.
On the one hand, Euclid's telescope and main camera will detect the minute deformations that the light from ancient galaxies has undergone to reach us. This effect, called gravitational lensing, is generated when light from a distant object, passing through regions of space where mass accumulates, is deflected by its gravity. The result is that the shape of the observed galaxy is distorted, and studying this distortion can provide information about the distribution of matter between us and the galaxy in question.
There are two general types of gravitational lensing. The so-called strong causes extreme deformations of objects located in the background, when its light passes close to very massive objects, such as clusters of galaxies, located between distant objects and our instruments.
But Euclid will use the much more common but extremely subtle weak gravitational lensing effect, which is generated when light from distant galaxies is distorted by matter distributed along our line of sight. These distortions are so tiny that it is only possible to detect them thanks to a powerful statistical study, through which the perceived shape of each galaxy is compared with an average generated by observing the hundreds of millions that make up the sample.
Since Euclid is primed to receive light from galaxies that emitted it some 10 billion years ago, the weak gravitational lensing method will yield an extraordinarily detailed map of how matter is distributed between us and those very distant regions (in space and in time) of the universe. And since dark matter is in the majority compared to ordinary matter, these maps will reveal the large invisible structures in which this type of matter is concentrated, which is still unknown to us.
However, the previous method cannot provide depth information along the line of sight, because the deformations of the galaxies are the result of the combination of the gravitational action of all the matter encountered in the way.
For this reason, Euclid will combine the method of weak gravitational lensing with the observation of how galaxies are grouped in the universe.
Shortly after the Big Bang, small heterogeneities formed in the dense plasma, which, with subsequent expansion, grew like bubbles and separated from each other. These asymmetries acted as seeds around which matter slowly accumulated and allowed large clusters of galaxies to form over the following hundreds of millions of years.
Euclid will analyze the light from some 35 million galaxies to map their spatial distribution. To do this, its infrared instrument will obtain the spectrum (decomposition) of the light of the objects, through which it is possible to know the distance at which they are from us. To complement this three-dimensional map of how galaxies are distributed and grouped when looking further and further away (that is, further and further into the past), the Euclid scientists will also take advantage of observations made by other ground-based observatories.
The combination of the commented observation methods will allow us to know how the structure of the cosmos and the distribution of matter have evolved in the last 10,000 million years.
The first partial data obtained by Euclid will be available in the year 2025, and later a more extensive delivery will be made in 2027. Finally, by the year 2030 all the observations that constitute the main mission phase will have been completed.
Then it will be the turn of the supercomputers. With them, the researchers will simulate, with theoretical models, how the structures and distributions of matter should be based on a variety of parameters, such as different models of energy and dark matter. In fact, the very existence of dark energy will be put to the test, since some of the models that will be tested will contemplate the possibility that, in fact, our understanding of the laws of gravity, on a large scale, is incorrect and that we do not such energy is needed to account for the accelerated expansion of the cosmos.
The Euclid mission will generate about 850 Gb of data per day. Storing, organizing and analyzing this enormous volume of information represents a real technological challenge, and different data processing centers will collaborate for this.
Among these centers, the Scientific Information Port of the Universitat Autònoma de Barcelona stands out, which has powerful parallel calculation capabilities and is already participating in important scientific projects, such as in the field of particle physics. This center will run some of the complex algorithms that will form the intelligence core of Euclid.
The launch on the 1st will be carried out by means of a Falcon 9 rocket from the SpaceX aerospace company and from Cape Canaveral in Florida.
Initially, the mission relied on the use of a Soyuz operated from Kourou, the ESA launch site in French Guiana. But as a result of the war in Ukraine, the option of using the Russian rocket was ruled out, and the analysis of a viable launch alternative caused the mission to be delayed by about 6 months.
Beyond the research on energy and dark matter, the gigantic volume of data that Euclid will obtain will feed, for decades, countless studies in the field of astrophysics and cosmology.
The catalog of 1,500 million galaxies will contain unprecedented information on their masses, distances and other characteristics, such as the rate of creation of stars in their interior, and will serve as a reference for the work of telescopes such as the James Webb or the radio antennas of the ALMA observatory in Chile.
Euclid is also expected to reveal a large number of objects in our own galaxy, too faint to be detected by ground-based observatories.
