2023-06-29 01:06:49
This is one of the greatest enigmas of astronomy: the Universe is made up of 95% of two mysterious dark components of which we know almost nothing, and on which the space probe Euclid will try to lift a corner of the veil.
The mission of the European Space Agency (ESA) will take off on Saturday at 3:11 p.m. GMT from Cape Canaveral in Florida, aboard a Falcon 9 rocket from SpaceX.
The two-ton probe designed by Thales Alenia Space will launch to its final position, 1.5 million kilometers from Earth. From there, Euclid, named following the inventor of geometry, will draw up a three-dimensional map of the Universe, encompassing two billion galaxies over a portion of one third of the celestial vault.
The third dimension of the map will be time: by capturing light from galaxies that have taken up to ten billion years to reach us, Euclid will delve into the past of the Universe, 13.8 billion years old.
Objective: to reconstruct its history by cutting it into “slices of time”, explained during a press conference the astrophysicist Yannick Mellier, head of the Euclid consortium, which brings together 16 countries.
In the hope of detecting the traces left by dark matter and dark energy during the formation of galaxies.
Dark matter and dark energy are of an unknown nature, but seem to govern the Universe, of which only 5% is composed of “ordinary” visible matter. A lack of knowledge that the head of the Euclid mission, Giuseppe Racca, describes as “cosmic embarrassment”.
– “Everything is going too fast” –
Without them, scientists cannot explain how the cosmos works. A puzzle that dates back to the 1930s, when Swiss astronomer Fritz Zwicky, observing the Coma cluster of galaxies, hypothesized that a significant part of its mass was invisible.
Almost 100 years later, the existence of this missing matter – called black because it neither absorbs nor reflects light – is a consensus. “When we look at the tip of the iceberg there is something we don’t understand: everything is going too fast”, summarizes David Elbaz, member of the Euclid collaboration.
The rotation speed of stars within galaxies – including that of our Sun – is so high that they should be ejected from them, “like a rocket that tears itself away from Earth’s gravity and takes off”, explains to the AFP this astrophysicist at the Atomic Energy Commission. Yet they stay there. “We deduce that there is an additional gravity which maintains them”, acting like a cement.
At the end of the 1990s, astronomers detected a second anomaly, on the scale of the entire Universe: the galaxies are moving away from each other more and more quickly, under the effect of a repulsive force called dark energy.
This acceleration of the expansion of the Universe would have started six billion years ago. Going back 10 billion years, Euclid might observe the first effects of dark energy and better identify it, its designers hope.
– Balloon –
But how to observe the invisible? By measuring its absence, by a warping effect called gravitational lensing: light from a distant object, such as a galaxy, is imperceptibly deflected by the visible matter and dark matter it encounters on the way to the observer.
“By subtracting the visible matter, we can + calculate + the presence of dark matter”, explains Giuseppe Racca.
“It is by watching this film of deformations in the history of the Universe that we will understand how dark energy behaves”, adds David Elbaz.
The scientist makes the comparison with a balloon on which lines are drawn with a marker to “see how quickly the balloon inflates” – which makes it possible to understand the effects of dark matter. As for the dark energy, it would be the breath that makes the balloon inflate.
Euclid has two instruments on board: a visible-light (VIS) imager and a near-infrared spectro-imager (NISP).
According to Yannick Mellier, this unprecedented cartography will constitute “a gold mine for astrophysics” allowing the study of the shape of galaxies, the birth of clusters, black holes…
And may help scientists finally get their hands on the mysterious particle that makes up dark matter, which escapes detection.
At a cost of 1.5 billion euros, the European mission must last until 2029 minimum.
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