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Euclid: A Dark Energy and Dark Matter Space Mission

Semper Ardens forskningsprojekt | 23/02/2018

The nature of dark energy and dark matter remains one of the most outstanding questions in science today. In order to secure Danish scientists first-hand access to all data in the European space mission Euclid, The Carlsberg Foundation has supported hardware contribution to the mission.

By Professor Kristian Pedersen, National Space Institute, Technical University of Denmark

The European space mission Euclid will enable the next leap forward in our understanding of some of the most enigmatic challenges of our time: the nature of dark matter and dark energy. 

A Semper Ardens Research Grant from the Carlsberg Foundation has supported the Danish hardware contribution to Euclid, which will secure Danish scientists first-hand access to all Euclid data. 

This direct involvement in Euclid will permit staff, postdocs and PhD students to conduct cutting-edge science for the next decades and build new scientific, technical and managerial expertise networks for Denmark in space science.

What Is the Euclid Space Mission about?

It is now well-established that the Universe is dominated by dark energy. It stems from the fact that the Universe’s expansion is accelerating, but the source of this acceleration is unknown and called “dark energy”. 72% of the matter-energy content of the Universe is dark energy and most of the remaining content is non-visible matter, “dark matter”, (23%), leaving only 5% in the form of “ordinary matter” making up all the objects shining in the sky, planets, moons, stars, gas, and dust.

"The nature of dark energy and dark matter remains one of the most outstanding questions in science today,” says Kristian Pedersen.

Dark energy is particularly intriguing and the next major step towards understanding the nature of dark energy requires dedicated space missions. European Space Agency’s (ESA) Euclid mission is devoted to unravelling the nature of dark energy. Euclid will over 6 years perform an unprecedented survey of that third of the sky which is not dominated by our own galaxy, the Milky Way. 

At the same time, Euclid will study dark matter in unseen detail as well as provide a gold mine of data, which can be utilised for a wealth of other scientific investigations, e.g. studying the most distant galaxies, clusters of galaxies, and exoplanets.

Euclid was approved by ESA in 2012 and since then the final design and construction of the satellite and its instruments have been on-going. The Euclid Consortium, which is responsible for providing and using the science instruments on Euclid, consists of more than 900 researchers and 500 engineers and technicians from most European countries.

Euclid Consortium meeting in Copenhagen 2012. 1450 members are registered in the Consortium, of which more than 900 are researchers in astrophysics, cosmology, theoretical physics and particle physics. More than 200 laboratories covering fields in astrophysics, cosmology, theoretical physics, high energy, particle physics and space science that are relevant for the Euclid missions are contributing to Euclid.

The Semper Ardens Research Grant from the Carlsberg Foundation has been instrumental in securing Danish scientists a key role in the Euclid mission. Hence, the annual Euclid Consortium Conference was organised by the Danish Euclid team and held in Copenhagen May 2013 with more than 350 participants (see figure).

Only through Danish hardware contributions Danish scientists will get direct access to all Euclid’s superb data as well as being able to influence the design of the mission. Accelerator experiments on the ground (e.g. LHC at CERN) and other astrophysical observations will provide interesting insights, but Euclid’s surveys from space will enable breakthroughs and offer an outstanding legacy database.

Science with Euclid

Euclid is mapping dark matter and dark energy by obtaining images and spectra of billions of galaxies.

Their light is collected with a 1.2 m telescope and focused on two large detectors: a visual light sensitive detector with exquisite image quality and an infrared detector (Near Infraread Spectrometer and Photometer, NISP) with filters and grisms enabling imaging and low resolution spectroscopy.

During 6 years, Euclid will map positions and distances of galaxies in that third of the sky, which is free from “obscuration” of stars, gas, and dust in the Milky Way. The shape of more than 1 billion galaxies will be determined and the distance to tens of millions of galaxies will be measured, providing an unprecedented 3D Cosmic map of the distribution of ordinary and dark matter. Since we are looking back in time when we look further out into the Universe, in effect Euclid is mapping how the distribution of matter in the Universe is developing with time. 

This development is driven by the amount and nature of dark energy and dark matter so through Euclid’s measurements we will be able to reveal intricate details of these intriguing components of Cosmos. A key question is whether the amount of dark energy stays the same over Cosmic time, which is the case if it is the Cosmological Constant, predicted by Einstein’s General Theory of Relativity, or if dark energy is due to a modification of, or an alternative theory to, General Relativity. In any case, Euclid will unfold fundamental properties of our Universe.

The Danish hardware contribution to Euclid, the Optical Ground Support Equipment, which consists of the telescope simulator (provided by Niels Bohr Institute) and the active telescope support (provided by DTU Space). Shown here is a sketch of the experiment set up in the vacuum tank at Laboratoire d’Astrophysique Marseille with the Euclid NISP detector.

Danish Participation in Euclid

The provision of hardware to Euclid is managed by the DTU Space, Technical University of Denmark, in close collaboration with the Dark Cosmology Centre, the Niels Bohr Institute, at University of Copenhagen. 

The Carlsberg Foundation grant has supported the man power required (in addition to the in-kind contributions from DTU Space and the Niels Bohr Institute) to design, proto-type and develop the Optical Ground Support Equipment (OGSE) instrument. This key instrument will be used to test the near-infrared NISP detectors under space conditions. 

The hardware parts have been procured through a supplemental grant from ESA. The OGSE has been constructed involving the Danish companies JJ X-ray and Copenhagen Optical Company and in close collaboration between DTU Space and the Niels Bohr Institute. The OGSE will be completed during 2018 and installed in a vacuum chamber at Laboratoire d’Astrophysique Marseille where the testing of the NISP detectors under space-like conditions will take place.

Euclid will provide exquisite scientific opportunities and Danish scientists will be in the frontline to get access to Euclid’s ground-breaking data. As a consequence, more than 25 scientists at the University of Copenhagen, the Technical University of Denmark and Aarhus University have already committed to the mission as members of Euclid’s Science Working Groups. 

It is foreseen that at least twice as many will use the Euclid database for addressing a wide range of scientific questions. Furthermore, numerous PhD projects, MSc, and BSc projects are foreseen to be carried out in preparation for Euclid - and many more when Euclid data are arriving from 2021.

Close up of the Telescope Simulator and the Active Telescope Support.

The Way Forward for Euclid

Euclid is planned for a launch in 2021 from ESAs space port, Kourou, in Guyana. In their own right, these data will enable detailed studies of the nature of dark energy and dark matter, but there are strong synergies with data from other space based and ground-based facilities.

In particular with the successor to the Hubble Space Telescope, the James Webb Space Telescope to be launched in 2019, the international sub-mm observatory, ALMA, and the European-Extremely Large Telescope, with projected first light shortly after 2020. Furthermore, the involvement in space near-infrared instrumentation for Euclid is a key step in building up Danish expertise and networks for participation in future space missions.

Danish contributions to Euclid enable fundamental discoveries about the structure and evolution of the Universe by Danish scientists. Euclid will foster a plethora of cutting-edge science projects for Danish PhD students, postdocs and staff for decades. Furthermore, a couple of Danish companies have been involved in the development and construction of the instruments and thereby strengthening hi-tech development in these companies and their collaboration with DTU and University of Copenhagen.

“The Universe is dark, but Euclid will enable a leap forward in our understanding of Cosmos so the future is bright!” - Kristian Pedersen

Kristian Pedersen about the Grant from the Carlsberg Foundation

The grant from the Carlsberg Foundation has enabled me to take a key position in the Euclid mission and thereby develop a stronger international network with, e.g. European Space Agency and internationally leading universities. This has established my standing in the Danish as well as the international astrophysics and space community and facilitated my ability to take up my current position as Director of DTU Space.