The universe has a hidden side, gigantic but beyond our reach. Evidence has been found that can be grouped around two concepts: dark matter and dark energy. Today we send our best investigator: Euclid.
What is Euclid?
Euclid was a Greek mathematician who lived three centuries before Christ. His extensive work laid the foundation for geometry – we also speak of Euclidean geometry. It is also the name chosen to christen a space mission: Euclid (USRopean vsosmian aIthe sky Iinvestigators of DArk Universe) scheduled to launch in 2023.
Led by the European Space Agency, the Cosmic Vision program mission is to deploy a new space telescope 1.5 million kilometers deep underground. A very remote area that is also home to the famous James Webb Observatory. But for Euclid his mission will be very different.
His goal is to unravel the darkest mysteries of the universe! That said, it seems exaggerated. Still, it’s true: Euclid is designed precisely to shed light on dark matter and dark energy. Two elements that are still very enigmatic today and whose observation represents the greatest difficulty for us. Yet the universe would be full of them.
Its working area will cover a little more than a third of the celestial sphere (35%). It will have nearly two billion galaxies in its field of view that it can map in 3D. It will also be able to trace the history of the cosmos as far back as 10 billion years (by targeting objects 10 billion light-years away).
It will thus be a new opportunity to study the expansion of the universe over such a long period of time, almost to its inception. The age of the universe since the Big Bang is almost fourteen billion years. For this task, Euclid will carry a 1.2 meter diameter mirror and two instruments: a near-infrared spectroimager and a visible-light imager.
Where is dark matter found?
This is precisely the mission of the Euclid researcher. In the universe, however, it is not yet clear where and how this dark matter is distributed. Yet they and dark energy made up almost 95% of the mass and energy of the universe! That means everything else, from stars to planets to the rest of visible matter, weighs “only” 5% of the total.
Dark matter is very strange. It neither emits nor absorbs light. It therefore eludes the instruments that can currently be used. Still, it has gravitational effects on galaxies. In this way we also try to measure it without observing it.
Because even though dark matter is invisible to our eyes, it still leaves traces of its presence. On a very large scale, its presence is likely to affect the light of distant galaxies. That’s what the accurate mapping of large parts of the Universe is all about to uncover these distortions and determine the distribution of dark matter.
Scientists have suspected the existence of dark matter since the early 1930s and it has been the subject of intense debate in the community due to the impossibility of observing it directly. Therefore, in order to make sense of the behavior of visible matter, astronomers have added the hypothesis of an invisible matter that would act on the former.
Visible matter corresponds to “ordinary” matter (also called baryonic). We know that it is made up of particles like the proton or the neutron that are at the heart of atoms. The composition of dark matter remains a mystery. We start from elementary particles, but there are several hypotheses that sometimes go very far in speculation. Currently none could be validated.
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What is dark energy (or dark energy) made of?
Just as mysterious as dark energy, if not more mysterious: black energy (or dark energy). This energy is thought to play a key role in the expansion of the Universe, causing galaxies to gradually move apart – with the appearance of an acceleration in the case of the most distant clusters of galaxies.
In the universe, if ordinary matter makes up 5% of the total 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 consideration. Also this year, studies have linked it to black holes that would emit something we don’t see.
As with dark matter, which causes multiple reflections, there are also some theories for dark energy. It is currently associated with Albert Einstein’s cosmological constant, which he envisioned in 1917. This constant is a parameter in his calculations to account for this phenomenon. Today this constant has been brought closer to this concept of dark energy.
Other hypotheses think of this strange acceleration of the expansion of the universe, like that of Quintessence. A sign that we still don’t know much about it: dark energy may not even be a form of energy. Nonetheless, it is present throughout the universe and plays a crucial role in its evolution.
When will the hunt for dark energy and dark matter begin?
The launch of the Euclid mission is scheduled for July 1 at the earliest. The telescope will be transported by a SpaceX rocket, the Falcon 9, from the Cape Canaveral launch site in Florida (USA). Then follows a journey lasting several months to position itself 1.5 million kilometers from Earth. We’ll have to wait years for the discoveries.
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