Euclid Telescope | A mission to study dark matter and dark energy

After a “perfect” take-off on Saturday, Europe’s Euclid space telescope is on its way to its vantage point, from where it will attempt to shed light on one of science’s greatest enigmas, dark matter and dark energy, which make up 95% of the Universe but about which we know almost nothing.

The satellite took off from Cape Canaveral, Florida, at 11:12 a.m. local time (Eastern time) aboard a Falcon 9 rocket from the American company SpaceX.

After separating from the rocket, it as expected emitted its first signal.

The two-ton telescope will be placed 1.5 million kilometers from Earth. The scientific work should begin in about three months, once the calibration of the instruments has been completed.

“It is such a joyful moment to see this mission on its way to its destination,” said Josef Aschbacher, its director general, during the live video of the European Space Agency (ESA).

The takeoff was “perfect”, added Carole Mundell, director of science at ESA. “Over the next six years, we will unravel the mysteries of the dark side of the Universe. »

The probe will draw a three-dimensional map of the Universe, encompassing billions of galaxies, over a portion of a third of the sky. The distant galaxies observed will make it possible to go back in time to 10 billion years ago – the time needed for their light to reach us.

opposing forces

Dark matter (25% of the Universe) and dark energy (70%) have opposite effects: when the first ensures the cohesion of galaxies, dark energy causes the expansion of the Universe.

For the first, dark matter, we know that it exists because of a mysterious observation: impossible to explain how a galaxy or a group of galaxies does not disperse by taking into account only the gravity of their visible elements (planets, stars, etc.).

“You have to hypothesize an additional quantity of matter, invisible to our telescopes, like a gravitational component that holds everything together,” explains to AFP Michael Seiffert, scientific manager of Euclid for NASA, who also participates. to this mission.

This cosmic “cement” has been dubbed dark matter.

Never observed directly, it could be subatomic particles, according to certain hypotheses.

Dark energy is perhaps even more enigmatic.

Since the discoveries of the famous astronomer Edwin Hubble in the 1920s, we know that the Universe is expanding. And since the 1990s, this expansion has accelerated.

But this “implies that on very large scales, gravity actually contains a repulsive component that pulls things apart,” says Seiffert. This force is dark energy, “a great mystery of physics”.

3D map

Lack of knowledge of these two dark components has been described as an “embarrassing situation” by the head of the Euclid mission at ESA, Giuseppe Racca.

The satellite therefore aims to better understand their properties, the way they act and evolve over time.

Thanks to its 3D map, the telescope will allow precise measurements on the distribution of galaxies and the expansion of the Universe.

From these observations, dark matter and dark energy will be deduced “indirectly”, explained Giuseppe Racca. Calculating dark matter can be done by “subtracting” visible matter.

And going back 10 billion years, Euclid could observe the first effects of dark energy, knowing that the acceleration of the expansion of the Universe would have started six billion years ago.

“Ultimate Answers”

At a cost of 1.5 billion euros, the European mission must last until 2029 minimum.

The telescope has two instruments on board: a visible-light (VIS) imager and a near-infrared spectro-imager (NISP).

The huge amount of data collected will be made available to the entire scientific community, after being analyzed by some 2,600 researcher members of the Euclid consortium, from around fifteen countries.

Euclid, named after the father of geometry, “will obtain data which is very useful for many other things than cosmology”, also recalled Marc Sauvage, member of the consortium and astrophysicist at the Atomic Energy Commission (CEA ).

NASA also plans to launch in 2027 a mission dedicated to the exploration of dark matter and dark energy, the Nancy Grace Roman space telescope.

These two missions will be “complementary”, judged Marc Sauvage. Making observations with different means allows “to ensure that our measurement is not biased by something that we do not know either”, he explained. The various experiments carried out “are not sensitive to the same biases of unknown origin, and it is by crossing them that we come to have ultimate answers”.