Exploring the "Euclid" of the Dark Universe

On July 1, 2023, the long-awaited Euclid telescope was finally launched on the Space X Falcon rocket. The Euclid telescope is part of the European Space Agency's scientific program. Its mission is to draw a 3D map of the universe and reveal the darkest secrets of the universe.

Whether in the United States or Europe, scientists classify telescopes according to their cost. The Euclid telescope is a medium-level (that is, M-level) mission. For example, the PLATO mission that has been established to discover and study exoplanets, and the ARIEL mission to study planetary atmospheres, are both medium-level missions. The Swift satellite that detects gamma-ray bursts and the TESS satellite that detects exoplanets, which we are very familiar with, are also medium-level missions.

In comparison, the Hubble Telescope we are familiar with and the Webb Telescope launched just two years ago are both large telescopes; while the X-ray telescope NuSTAR and the IXPE telescope that detects X-ray polarization are both small telescopes because of their relatively low cost.

Hubble Telescope in orbit | Tuchong Creative

After launch, it will take about a month to reach its final destination at the end of July, the Lagrange Point 2 (L2), 1.5 million kilometers from the Earth. So, what is a Lagrange point? There are usually five relatively stable points around two massive celestial bodies, which are called different Lagrange points. On the line between the sun and the earth, there are L1, L2 and L3, of which L1 is located in the middle of the sun and the earth, L3 is closer to the sun, and L2 is closer to the earth. In addition to these three points, there are two points, L4 and L5, on both sides of the earth and the sun. In comparison, L2 is farther from the sun, is less disturbed, has better observation conditions, and can be observed for a long time, so some telescopes were launched to the L2 point.

The Euclid telescope is 4.7 meters long and 3.7 meters in diameter. It mainly consists of a telescope with a primary mirror of 1.2 meters in diameter, covering an area of ​​0.5 square degrees. It contains a visible light camera and a near-infrared spectrometer and photometer. These instruments will measure the precise position and shape of galaxies in visible light and the redshift of galaxies in infrared light, from which their distance can be derived. During the mission, which will last at least six years, an international consortium of scientists from 13 European countries and the United States, Canada and Japan will use the Euclid telescope to observe an area of ​​about 15,000 square degrees, about one-third of the sky.

By then, the Euclid telescope will have accomplished some amazing feats, including

1. Create the largest and most accurate three-dimensional map of the universe to date, containing 2 billion galaxies;

2. Describe the morphology, brightness and spectral properties of astronomical sources;

3. Observe about 10 billion astronomical sources, including 1 billion weak gravitational lenses;

4. Measure the spectral redshift of at least 30 million celestial bodies to study galaxy clusters;

5. Three areas of the sky will be repeatedly observed, the so-called deep fields of the Euclid telescope, covering a total of 50 square degrees. These three areas will be visited regularly throughout the mission and will be used as calibration fields to monitor the stability of telescope and instrument performance.

From the above figures, you may have felt the power of the Euclid telescope. So what cosmic mysteries will it solve? We know that stars, planets, gases and all visible things only account for 5% of the total composition of the universe. The other 95% is made up of dark matter that maintains the stability of galaxies and dark energy that drives the accelerated expansion of the universe.

However, we know very little about the nature of dark matter and dark energy! By observing the evolution of the universe over the past 10 billion years, the Euclid telescope will reveal how the universe expanded and how the structure of the universe was formed, thus bringing more information related to dark matter and dark energy.

In addition, with its wide sky coverage and catalog of billions of stars and galaxies, Euclid will also provide a rich target source for the Webb Space Telescope and the Atacama Millimeter-submillimeter Array, as well as future missions such as the European Extremely Large Telescope ELT, the Thirty-meter Telescope TMT, the Square Kilometer Array SKA, and the Vera Rubin Observatory in Chile. Here, I also sincerely look forward to more surprises from Euclid.

This article is a work supported by Science Popularization China Starry Sky Project

Author: Gou Lijun

Reviewer: Li Haining

Produced by: China Association for Science and Technology Department of Science Popularization

Producer: China Science and Technology Press Co., Ltd., Beijing Zhongke Xinghe Culture Media Co., Ltd.