2023-07-02 04:00:15
On knows that the universe is expanding, that is to say that it stretches, each star moving away from the others. But we still don’t know why, and also why this expansion is accelerating under the effect of a mysterious dark energy. In this expanding universe, how do large structures form and evolve under the influence of gravitation?
Why is the gravitation generated by the matter composing gases and galaxies of these structures not enough? Is there a matter invisible to our eyes, to our instruments, a dark matter?
This is what will try to highlight Euclid, an unprecedented mission from the European Space Agency (ESA), which has just been successfully launched on July 1, 2023 and in which France plays a major role. The Euclid mission brings together a consortium of more than 1,600 people, including 350 in France, spread over 250 laboratories in seventeen countries.
Go back in time to understand the expansion of the Universe
Euclid will image billions of galaxies, images that travel at the speed of light. been emitted, that is to say in the past: the further away they are, the older the received image.The expansion, the lengthening of the frame of the universe also causes a stretching of the spectra of light towards long wavelengths, and for visible light (Visible light, also called visible spectrum or optical spectrum is the part of…) towards red, even infrared.
Euclid will stay in space next to the James-Webb space telescope and the Gaia probe, at the Lagrange point (A Lagrange point (denoted L1 to L5), or, more rarely, libration point, is a.. .) 2, which makes it possible to be relatively sheltered from the sun’s rays.
ESA. Acknowledgement: Work performed by ATG under contract for ESA, CC BY-SA
This “redshift” makes it possible to determine the distance at which the source is located and therefore indirectly to locate the time when the light was emitted (by using for example the “hubble diagram”). Euclid will therefore determine the redshifts of the galaxies it will image, to reconstruct the evolution of our universe over the last ten billion years.
Thus, by observing the distribution of galaxies forming the great structures of the universe at different times, Euclid will help us understand why the fabric of the universe is expanding (and therefore why celestial objects are moving away from each other) , but also why this expansion is accelerating under the effect of a mysterious “dark energy”.
A representation of the cosmic web, that is to say the large structures that form the universe (clusters of galaxies grouped into filaments), from the SDSS (Sloan Digital Sky Survey) astronomical survey.
M. Blanton and the Sloan Digital Sky Survey, CC BY
Can we see dark matter?
Euclid will also allow us to tackle the second great cosmological mystery, that of “dark matter”. This unusual material is introduced into astrophysical theories to account for various observations (Observation is the act of attentive monitoring of phenomena, without the will to them…) (masses of galaxies and clusters of galaxies, fluctuations of the diffuse background cosmological). In other words, without dark matter, we cannot predict what we see, even with the most sophisticated theories we have regarding the Universe.
But the main characteristic of dark matter is that it interacts very little with matter and light (hence its name): how, under these conditions, can we hope to detect it? Euclid proposes to detect and locate dark matter indirectly by studying its gravitational effect on the image of galaxies. To do this, Euclid will use the phenomenon gravitational lenses which “bend” the light rays passing through a gravitational field, and thus distort the image of the galaxies crossing it. It is by studying these image deformations that it will be possible to reconstruct the dark matter present.
Thus, Euclid will allow us to map the no less mysterious “dark matter” which participates, with the visible matter of stars and nebulae, in the gravitational effects which link stars within galaxies and galaxies within clusters.
Euclid will observe from space to avoid looking through Earth’s atmosphere. Indeed, it is turbulent, which disturbs the images and affects their resolution; and infrared radiation is highly absorbed by water and carbon dioxide molecules mainly present in the atmosphere, which strongly limits the possibility of producing images and spectra in this wavelength range. It will image everything that is possible to see beyond the Milky Way (The Milky Way (also called “our galaxy”, or sometimes…), i.e. regarding a third of the celestial vault, the rest being hidden by the galactic plane (disk in which the stars of our galaxy rotate) and by the ecliptic plane (disk in which the planets of our solar system rotate).
The telescope and its instruments
The satellite is equipped with a Korsch type telescope with 3 mirrors which offers a large field of view, equivalent to two and a half times the surface of the lunar disc. It was made by Airbus Defense and Space in Toulouse, entirely in silicon carbide (SiC), a thermally very material. It is maintained at a temperature of -140°C (temperature is a physical quantity measured using a thermometer and…) and incorporates two instruments, the NISP and the VIS.
The Euclid satellite following its successful tests, to ensure that it does not suffer from electromagnetic interference from its own instruments. The tests are carried out in a specially insulated chamber at Thales Alenia Space in Cannes.
ESA-Manuel Pedoussaut, CC BY-SA
The NISP (for near infrared spectro photometer) is an infrared spectro-photometer simultaneously producing images of galaxies while dispersing their light to produce spectra. Its large focal plane of 66 million pixels, working in the near infrared (0.9 to 2 micrometers) and cooled to -180°C, offers the largest infrared field of view ever achieved for a space mission. The opto-mechanical part of the instrument is also made of SiC. The NISP is under French responsibility, carried out under the supervision of the Marseille Astrophysics Laboratory.
To follow the evolution of the structures at different times, the distances will be determined by the “BAO method” (acoustic oscillations of baryons), a method of obtaining a standard ruler, a dimensional standard for measuring distances. The goal is to process 35 million galaxies.
The VIS (visible instrument) is a camera producing images in visible wavelengths (0.55 to 0.9 micrometers), of English responsibility, on which are present 3 French contributions, in particular its immense focal plane totaling approximately 600 million pixels (equivalent to 300 HD televisions), the second largest ever made for a space mission following Gaia, enabling the visualization and characterization of 50,000 galaxies in a single image.
It is also made of SiC and maintained at a temperature of -120°C. There distortion of some galaxy images due to weak gravitational lensing induced by the effects of gravitation due to the presence of matter between these galaxies and the telescope will make it possible to highlight and locate dark matter. The goal is to process one and a half billion galaxies.
Distances will be determined by measuring the “redshift” of each source observed by spectrometric methods (instrument NISP) et photometric (VIS instrument) resulting from luminosity measurements carried out on board and supplemented by the assistance of telescopes on the ground.
The two instruments will generate approximately 850 Gb of data each day to be transmitted to Earth. The satellite incorporates a 4Tbit mass memory storing scientific data and telemetry data related to the operation of the instruments. It sends this data every day for four hours to the Cebreros ground station in Spain, which then transmits it to the Mission Operations Center located at ESA’s ESOC Center in Darmstadt, Germany.
Cumulated over the six-year mission, the volume of data to be processed is impressive, around 170 million gigabytes. This represents several hundred thousand personal computer hard drives. The treatment will be carried out in nine treatment centers, eight in Europe and one in the United States. For France, the computing center of the National Institute of Nuclear Physics and particle physics (Particle physics is the branch of physics that studies constituents…), in Villeurbanne alone will process 30% of the data.
1688270838
#Euclid #telescope #discover #Dark #Universe #neighbor #JamesWebb
