Euclid, the exciting European space mission searching for dark matter and dark energy

We have found names for them, they are estimated to make up 95% of the universe and yet we know almost nothing about them. They are Dark matter and dark energy. It is still considered too obscure for the taste of scientists whose theories and fantasies have been nurturing for several decades.

“All we know is that the first has gravitational pull and the second causes an accelerated expansion of Universe Giuseppe Racca recalls European Space Agency (Esa). Her exact nature is still unknown, and given her preponderance, she is considered a true “cosmic embarrassment”, as is the person responsible for the mission that Isa is about to launch to reveal her secrets. In Cannes, in the clean rooms at Thales Alenia Space where they are assembled, Euclid satellite Ready to take off. It should take off this summer and remain in orbit for at least six years to produce a 3D map of some two billion galaxies.

And it is this mass of unpublished information, analyzed by hundreds of scientists, that should enhance our knowledge of … dark matter. how ? And what are the possible revelations? 20 minutes They went to meet some of these specialists at the manufacturer, near Croisette, where they met this week.

What is the purpose of this three-dimensional mapping of two billion galaxies?

With this €1.5 billion mission, the European Space Agency hopes to answer at least two questions: “What is the origin of the universe?” and “Why is it expanding at an accelerated rate instead of slowing down due to the gravity of matter?”. Because of this, “Euclidean’s great advantage lies precisely in the number of observable galaxies,” explains Stephanie Escoffier, director of research at the National Center for Scientific Research. “We’re going to multiply it by ten, and inevitably, the more there are, the more accurate our results will be. These 3D maps should be a real revolution.”

By comparison, the Hubble Space Telescope has observed the sky above 25 square degrees (a unit of space measurement seen from Earth) in 25 years, while a new satellite will be able to capture ten square degrees a day! “We will be able to study the distribution of these galaxies in a very precise way, which will inform us about dark energy, but also analyze their deformation, which will be able to give us information on the location of dark matter,” explains the researcher.

Scientists should therefore be able to understand this “invisible” by determining the extent of its absence. you follow? It will be based on the “gravitational lensing” effect, that is, when a celestial body deflects rays emitted by a light source, “to measure the amount of matter between the satellite and the observed galaxy.”

How will the task work?

Launched from Cape Canaveral aboard a SpaceX Falcon 9 rocket this July, Euclid is expected to reach its destination in October. From its orbit around the sun, 1.5 million kilometers from Earth, the telescope will relentlessly image the depths of the universe until 2029, and possibly beyond, if all goes well. Equipped with an impressive sensor of more than 600 million pixels, it will provide images “with which we can zoom in infinity,” explains Pierre Cassneuve, responsible for the Cnes program, the National Center for Space Studies. To target this or that galaxy.

That will be for the visible part. The second instrument, the “Near Infrared Spectrophotometer and Photometer,” will then allow “cosmologists to estimate our distance from the galaxy in question,” describes the Thales Alenia spacecraft. So, thanks to him, the resulting cartography will be modeled in 3D.

As a result, hardly imaginable amounts of information, which will be distributed in several data centers in Europe. “We would have to process 26 petabytes a year,” or 26,000 terabytes, “and for comparison, the Hubble satellite has a volume of 160 terabytes every year,” assures Giuseppe Racca, mission chief at the European Space Agency (ESA). We’re excited, but also a little scared. We’ll have to deal with a data monster, warns French astrophysicist David Elbaz, director of research at the Atomic Energy Agency (CEA), too. The latter is part of a consortium of 1,500 scientists (in six th country) they’ll have to dissect everything.

What can we expect from these results?

Euclid will scan the sky through space, but also through time. The machine, named after the mathematician considered the “Father of Engineering,” will be able to capture light that took up to ten billion years to reach. “Thus we will be able to see if dark energy is a cosmological constant or if it is something that will evolve over time or if we have to question Einstein’s general relativity,” notes Stephanie Escoffier. That’s it.

And what Euclid can help discover really fascinates David Elbaz. “This designation can allow us to infer what is the origin of our origins. Was everything born of gravity as we know it, with the apple falling from the tree? Or that when I put this apple very, very far from the ground and drop it, it no longer does the same thing, or They even explode and come back,” explains the specialist, with little idea for an answer. “Some distant objects that we notice, instead of collapsing on each other, repel each other. It’s similar to something called antigravity.”

But what creates this antigravity? It is all the theories envisaged on the subject that can be rigorously tested by this ESA mission. To characterize the still very mysterious nature of dark energy, which is responsible for accelerating the expansion of the universe. “Is it a ‘property’ of space, according to the answer given by Einstein? Is it the quantum vacuum as others say? Or is this another crazy possibility where this energy, which we call phantom energy, will tear galaxies apart, then stars, then molecules, then atoms, all What do you have with the Big Bang. Where you will redo everything until there is nothing left. Not even an atom of hydrogen. “If the first images of Euclid are expected this fall, then the first results of their analyzes will not come before a year and a half.

Fabian Benacchi