4 questions about Euclid, the task that must reveal the dark secrets of the universe

What is Euclid?

Euclid was a Greek mathematician who lived three centuries BC. His great work laid the foundations of geometry – we are also talking about Euclidean geometry. It’s also the name chosen to christen a space mission, Euclid (weshrimp againstosmotic aIthe sky Iinvestigator Drcosmos ark), scheduled for launch in 2023.

Led by the European Space Agency, as part of the Cosmic Vision programme, the mission consists of deploying a new space telescope deep within the Earth, at a distance of 1.5 million kilometres. A very remote area where we also find the famous James Webb Observatory. But for Euclid, his task would be very different.

His goal is to unlock the darkest secrets of the universe! Said like that, it seems exaggerated. However, that’s true enough: Euclid’s cut was precisely cut to shed light on dark matter and dark energy. Two very mysterious elements remain to this day, and we have much more difficulty noticing them. Yet the universe will be filled with them.

It will cover just over a third of the celestial sphere (35%). It will have in its field of view nearly two billion galaxies, which will be able to draw three-dimensional maps. It will also be able to trace the history of the universe up to ten billion years ago (by targeting objects 10 billion light-years away).

Thus, it will be a new opportunity to study the expansion of the universe during this vast period, almost to its very beginnings. The age of the universe since the Big Bang is approximately fourteen billion years. For the task, Euclid will carry a 1.2-meter-diameter mirror and two instruments: a near-infrared spectrophotometer and an imager observing in visible light.

Where is dark matter located?

This is precisely the task of Euclid’s investigator. in the universe, but it is not yet clear where and how this dark matter is distributed. However, dark energy made up nearly 95% of the mass and energy of the universe! Which means that everything else, from stars to planets, to the rest of visible matter, weighs “only” 5% of the total.

Dark matter is very strange. It does not emit or absorb light. So he gets away with the current tools that can be used. However, it does have an effect on galaxies through gravity. This is also how we try to measure it without noticing it.

Because if dark matter is not visible to our eyes, it leaves traces of its existence. On a very large scale, its presence is likely to affect the light of distant galaxies. This is the whole point of meticulously mapping large swaths of the universe to expose these distortions and determine the distribution of dark matter.

Scientists have suspected the existence of dark matter since the early 1930s and it is the subject of fierce debate in society, as it is impossible to observe it directly. To give meaning to the behavior of visible matter, astronomers added the hypothesis of invisible matter, which would act on the former.

Visible matter corresponds to “normal” (also called baryonic) matter. We know that it is made up of particles such as a proton or a neutron, which are found in the cores of atoms. For dark matter, its formation remains a mystery. We assume the existence of elementary particles, but there are many hypotheses that sometimes go too far in conjecture. Nothing can be validated at this time.

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What is dark energy (or dark energy) made of?

As mysterious as dark energy, if not more: black energy (or dark energy). This energy is suspected to play a major role in the expansion of the universe, by causing galaxies to gradually move away from each other – with an impression of acceleration in the case of groups more distant from each other.

If ordinary matter in the universe accounts for 5% of all mass and energy, then dark matter and dark energy make up the remaining 95% (25% for one, 70% for the other). The nature of this dark energy is also the subject of intense reflection. Again this year, studies linked it to black holes, which would emit something we don’t see.

As in the case of dark matter, which gives rise to a variety of reflections, dark energy also has its share of theories. At the moment, it is associated with cosmological constant For Albert Einstein, who imagined it in 1917. This constant is a benchmark in his calculations to take this phenomenon into account. Today, this constant has been brought closer to the concept of dark energy.

Other hypotheses turn to thinking of this strange acceleration of the expansion of the universe, such an acceleration in essence. A sign that we still don’t know much about it, dark energy may not even be a form of energy. Yet it is found throughout the universe and plays a crucial role in its evolution.

When does the search for dark energy and dark matter begin?

The Euclid mission has been scheduled for July 1 at the earliest. The telescope will be flown by a SpaceX Falcon 9 rocket from Cape Canaveral launch pad in Florida (USA). Then it will follow a few months’ journey to position itself 1.5 million kilometers from Earth. For discoveries, we have to wait for years.

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