The Euclid Mission: Exploring the Dark Corners of the Universe
The Euclid space telescope blasted off from Cape Canaveral in Florida on July 1, 2023, and will end in 2028. The €1.4 billion mission, operated by the European Space Agency (ESA), is a noble mission to observe and document 1 billion galaxies and help discover the solution to a complex problem that can unravel the base rules of universal evolution. Euclid will explore how the structure of the Universe expanded over time, reveal the role of gravity in this expansion, and uncover the nature of dark energy.
What is Dark Energy?
Dark energy is a theoretical form of energy that is the main force affecting the accelerating force of the Universe. A common assumption formulated by the lambda-CMD model of cosmology states that the total amount of energy in the observable Universe consists of 68% dark energy, while matter, dark matter, and photons comprise the remaining 32%. That might come as a surprise, as dark energy has a density of only 7×10-31 g/cm3, which is significantly lower than matter or anti-matter. It is rather substantial due to its uniform presence throughout space.
Even though the existence of dark energy is strictly hypothetical, several pieces of evidence could support its existence. The first type of evidence comes from observations of supernovae. A supernova is an extremely bright star explosion, representing the last stage of its life. Even though there are several types of supernovae, the one that is important in this scenario is the type Ia supernovae. An Ia supernova has a consistent peak brightness, which scientists use to find its intrinsic luminosity and distance from Earth. Using the standard candle method, luminosity L, distance D, and apparent brightness b, we can construct the following formula:
L = 4πd2b
By substituting all of the required values into the formula, we can find the distance from any supernova from Earth. By comparing the resulting distance to the redshift, the increase in wavelength of electromagnetic radiation shows that the universal expansion is accelerating. This was the first initial proof of the existence of dark energy, and many more have followed up since then.
How does the Euclid Mission fit into all of this?
One of Euclid's missions is to find the nature of dark energy. To do this, Euclid will observe the current Universe and how it evolved over the past 10 billion years. From this information, astronomers can infer the nature of dark energy and how the universal expansion affected its structure and evolution.
ESA's Euclid is designed to explore the composition and evolution of the dark Universe. By accurately mapping the shape, positions and distance of a huge number of galaxies, the space telescope will create a 3D map of the large-scale structure of the Universe across space and time out to 10 billion light-years, and across more than a third of the sky.
The module consists of three separate sections: a 1.2 m diameter telescope, a visible-wavelength camera (the VISible, VIS), and a near-infrared camera/spectrometer (the Near-Infrared Spectrometer and Photometer, NISP). The telescope can collect light from all sources it observes, such as galaxies. The light is then directed onto the VIS camera to provide incredibly sharp images. The NISP spectrometer will provide visuals and spectroscopic data through the lens of a near-infrared camera.
The reason why universe-monitoring missions use near-infrared equipment is due to the information they reveal. Different wavelengths of light reveal aspects of the Universe that may remain hidden from others. One of the main advantages of including near-infrared equipment in Euclid is that it can observe objects through interstellar dust. If interstellar dust blocks a light-emitting object, the near-infrared system will successfully detect it, while the traditional camera will not. It also reveals beautiful colours in many seemingly empty patches of space. An example is the image below, obtained by combining VIS and NISP data.
What Has The Mission Uncovered So Far?
On May 23, 2024, Euclid released five unique photographs. The images demonstrate its ability to unravel the secrets of the cosmos and enable scientists to hunt for rogue planets, use lensed galaxies to study mysterious matter, and explore its evolution.
“Euclid is a unique, ground-breaking mission, and these are the first datasets to be made public – it’s an important milestone. The images and associated science findings are impressively diverse in terms of the objects and distances observed. They include a variety of science applications, and yet represent a mere 24 hours of observations. They give just a hint of what Euclid can do. We are looking forward to six more years of data to come!”
Valeria Pettorino, ESA’s Euclid Project Scientist
The images obtained by Euclid are at least four times sharper than those taken with ground-based telescopes. They cover many large patches of the sky due to the scope of the equipment and survey distant galaxies with incredible detail. The images are the following:
Abell 2390
Abell 2390 is a galaxy cluster, a structure of countless galaxies kept together by gravity, 2.7 billion light-years away from Earth, located in the Pegasus constellation. By analysing the image of Abell 2390 alone, we can see it consists of more than 50,000 galaxies. The distances between these galaxies are measured through the new observations provided by Euclid. Based on weak gravitational distortion of galaxies lying in the background, dark matter distribution is detected in Abell 2390. Because of this, Abell 2390 is considered a substantial reserve of dark matter, which makes it perfect for studying the effects and properties of dark matter.
Euclid indirectly measures the amount and distribution of dark matter in a galaxy cluster via gravitational lensing. This is a phenomenon where the light travelling to us from more distant galaxies is bent and distorted by this mysterious matter. Thanks to Euclid’s advanced instruments we can see an especially beautiful display of lensing in Abell 2390, with multiple giant curved arcs, some of which are actually multiple views of the same distant object.
Messier 78
The image showcases Messier 78, a star formation enveloped in dust. Euclid captured the first-ever image of this young star-forming region at these dimensions, which only goes to show its versatility.
Euclid discovered over 300,000 new objects through this perspective alone, providing data for understanding universal evolution. ESA scientists are using the data to catalogue the number of stellar and sub-stellar objects within Messier 78, which is necessary to uncover their development throughout history. Furthermore, sub-stellar objects can give us more information about dark matter. Sub-stellar objects are bodies with masses less than that of a typical star, unable to support main sequence hydrogen burning. Examples include brown dwarfs and former rogue stars.
The top of the frame invites us to see the reflection nebula NGC 2071. It was first discovered on January 1, 1784, by William Herschel. Reflection nebulae are clouds of dust that reflect the light of nearby stellar objects, shown as purple clouds in the image.
NGC 6744
NGC 6744 is one of the largest spiral galaxies outside our nearby Universe. NGC 6744 is an intermediate spiral galaxy in the Pavo (Peacock) constellation within the Virgo Supercluster. The galaxy forms most of the stars in the nearby Universe, which makes it an object of study concerning dark energy.
Euclid reveals the typical elongated spiral structure, all through a combination of wavelengths. These details include thin lanes disconnecting from the spiral arms, which Euclid can do without losses in quality or clarity. The data from this image will allow scientists to document all individual stars within NGC 6744, trace the distribution of bodies within the galaxy, and map star formation by observing the gasses and dust often associated with it. Since stars are the main components of every galaxy, seeing how they grow and evolve is key to understanding why we see the Universe as it is today.
Abell 2764
The image above includes the Abell 2764 galaxy cluster in the top right. This region is incredibly dense, consisting of hundreds of galaxies orbiting each other with the help of dark matter. The mass of Abell 2744, also called Pandora's Cluster, is split across several components. 5% of its mass are its galaxies, 20% gas, and 75% dark matter. The high concentration of dark matter impacted the development of the cluster throughout its existence, making it an appropriate topic of study.
Euclid captures not only this galaxy cluster but also countless background galaxies and distant galaxy clusters, all in great detail. The image will allow scientists to determine the radius of the cluster and study its outskirts with faraway galaxies still in the frame.
Dorado Group
The Dorado Group of galaxies is an incredibly galaxy-rich area in the southern hemisphere, lying 62 million light-years away in the constellation of Dorado. The Dorado Group is relatively young, as many galaxies are still forming. Furthermore, many of its stars are still interacting with each other at various stages of merging. The size of the Dorado Group is somewhere between larger galaxy clusters and smaller galaxy groups, which makes it ideal for Euclid to study with its instruments.
Scientists are using the data to compile a complete document of individual star clusters around Dorado galaxies. By figuring out the position of these clusters, scientists will then trace how all the individual galaxies formed and understand their content structure.
