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The European Space Agency’s €1.4bn space telescope has blasted off on a mission to map billions of galaxies across the cosmos, helping scientists to understand the mysterious “dark energy” and “dark matter” that are believed to dominate the universe.
The Euclid observatory set off on schedule on Saturday towards its observing point 1.5mn km from Earth on a Falcon 9 rocket made by Elon Musk’s SpaceX. Success of important moments of the launch from Cape Canaveral in Florida was greeted with applause — particularly when the 2-tonne satellite sent an independent signal back to the control room after separation from the rocket’s last stage.
An emotional Carole Mundell, ESA science director, said: “It is difficult to find words to describe my feelings. This mission has been 15 years in the making. [Its] next six years will unravel the mysteries of the dark universe.”
The consensus view among cosmologists is that all the visible matter known to scientists, from galaxies down to subatomic particles, accounts for just 5 per cent of mass and energy in the entire universe.
Dark energy, making up 70 per cent, seems to be a property of space itself, expanding the cosmos at an increasing rate. Counteracting this is the gravitational pull of dark matter, which accounts for 25 per cent and has mass but no other measurable characteristics.
“There are hundreds of models for what dark matter and dark energy might be but we have no idea which might reflect reality,” said Adam Amara, director of the University of Portsmouth’s Institute of Cosmology and Gravitation.
“In 2005 a tiny group of us proposed a space telescope to investigate the dark universe. Now close to 3,000 people have worked together to make this dream a reality,” he said.
Euclid — named after the ancient Greek mathematician regarded as the father of geometry — was originally destined for launch on a Russian Soyuz rocket but the plan fell victim to the rupture in relations following the country’s full-scale invasion of Ukraine.
ESA turned instead to SpaceX and Falcon 9. Finding a different launcher and reconfiguring the spacecraft delayed the mission by no more than a year.
In about a month Euclid will reach its destination, the “second Lagrange point” 1.5mn km away, where gravity from the Sun and Earth exactly balance the satellite’s orbital motion, so it appears to hover in the same place in space. The James Webb Space Telescope is located nearby.
There it will map the universe by observing galaxies out to 10bn light-years away across 36 per cent of the sky that is not obscured by stars and dust in Earth’s own Milky Way galaxy.
“We’ll be able to reconstruct the cosmic history of the universe for the last 10bn years,” said Euclid consortium lead Yannick Mellier of the Institut d’Astrophysique de Paris.
Changes in the movement and distribution of galaxies and the way they cluster together will reveal the dark universe’s influence. Dark matter tends to pull galaxies together through the force of gravity, while dark energy pushes them apart as it accelerates the expansion of the universe.
Two cameras are attached to Euclid’s 1.2-metre telescope. One, led by UK scientists, records in visible light. The other, led by French researchers, operates in the near-infrared spectrum.
Mark Cropper of University College London has led the design and development of the visible camera for 16 years.
“The instrument will image a large swath of the distant universe with almost the fine resolution of the Hubble Space Telescope, observing more of the universe in one day than Hubble [has done] in 25 years,” he said. “The universe on this scale has not been seen in this level of detail.”
Whether an intrinsic property of empty space, a “vacuum energy” of virtual particles as predicted by some quantum physicists or a previously unknown energy field, scientists hope that the telescope’s images will help define dark energy. Their findings could even offer evidence for a fundamental revision of Einstein’s theory of gravity.
Possible explanations for dark matter vary just as much, said Amara. Candidates range from tiny particles that interact with ordinary matter only through their gravitational force, to black holes formed shortly after the Big Bang that still pervade the universe.
Amara does not think dark matter will have a simple explanation. “If you think of all the ordinary matter in the universe, it takes an enormously rich and complex diversity of forms,” he said. “There could be an equally diverse universe of dark matter out there.”
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