Kapitel 6: DEEP SPACE OBJECTS THROUGH EUCLID'S EYES
Perseus Sky Cluster
This snapshot of Euclid shows 100 candidate galaxies in the Perseus cluster and more than 100,000 other galaxies in the background, each containing hundreds of billions of stars. Many of these faint galaxies have never been seen before. Some of the galaxies in this field of view are so distant that their light has taken 10 billion years to reach us. By mapping the distribution and shapes of these galaxies, cosmologists will be able to learn more about how dark matter shapes the universe. This is the first time such a large area of the deep sky has been imaged, capturing a large number of Perseus galaxies. Perseus is one of the largest known structures in the universe, 240 million light-years from Earth. Astronomers have shown that clusters of galaxies like Perseus can only form if dark matter is present in the universe.
Gravity causes dark matter to form filamentary structures commonly called the cosmic web. The transition points between dark matter filaments allow galaxies to come closer together and form clusters. Euclid in particular seems likely to reveal dwarf galaxies composed of older stars. Dwarf galaxies are very difficult to capture in optical images. These faint galaxies, consisting of several billion stars, are expected to be discovered in the EUT's infrared images. These galaxies have begun to be identified in images of the Perseus cluster. At the same time, the shapes of these dwarf galaxies will be studied to understand the distortions caused by weak lensing and thus how dark matter is distributed in the galaxy cluster.
spiral galaxy: IC342
One of the first galaxies observed by Euclid, IC 342 or Caldwell 5 is also known as the "Hidden galaxy". IC 342 is difficult to observe because it lies behind the dense disk of the Milky Way galaxy, blocking our view of gas and dust. The EUT's near-infrared camera allows you to look through the dust and can be used to measure the light from cool, low-mass stars that make up a significant portion of the galaxy's mass. It might be thought that this image could be obtained with large-diameter telescopes, but this is not true. What makes Euclid's image special is that a wide image can be taken covering the entire galaxy, and at the same time, as we move around the image and zoom in, we can distinguish single stars and star clusters. These advantages can help us trace the history of star formation and understand how stars form and evolve over the lifetime of the galaxy.
IC 342 is about 11 million light-years from Earth. This galaxy, which covers an area approximately the size of a full moon in the sky, resembles our own galaxy and has a spiral structure. It is important to observe galaxies like IC 342 to learn more about our own galaxy and similar galaxies, which are difficult to observe in their entirety because we are inside it. In the image taken by the EUT of this galaxy, which was also observed with the Hubble Space Telescope, many previously unknown globular star clusters were identified, as well as information on the history of star formation.
Irregular Galaxy NGC 6822:
To create a three-dimensional map of the universe, Euclid will observe light from galaxies 10 billion light-years away. Most galaxies in the early universe do not appear to have regular spiral shapes, but are irregular and small in size. These galaxies are the building blocks of larger galaxies like our own.
The EUT observed the dwarf irregular galaxy NGC 6822, located about 1.6 million light-years away. This galaxy, a collection of stars, gas and dust, is a member of the same galaxy cluster (Local Group) as the Milky Way. Although NGC 6822 has been observed many times since its discovery in 1884, and more recently by the James Webb Space Telescope, Euclid was able to image the entire celestial island and its surroundings in high resolution (far higher quality and detail than ground-based telescopes and other space telescopes can provide) for the first time in an hour.
NGC 6822 is a galaxy with a very low density of elements heavier than hydrogen and helium. These heavy elements are metals that were not expected to be abundant in the early universe and that increased in abundance after the first generation of stars ended their lives. Researchers on Euclid's science committee believe that analyzing Euclid data on galaxies with low metal densities, such as NGC 6822 in our own galactic neighborhood, could yield insights into how galaxies evolved in the early universe.
The wide-field imagery and color information recorded by Euclid's near-infrared camera have identified a number of globular clusters that provide clues about the galaxy's formation and how it came together. Globular clusters are collections of related stars in which hundreds of thousands of stars are held together by gravity. These groups are old objects from the universe that formed from the same cloud. Globular clusters therefore "preserve the fossil record" of the early star-forming periods of their host galaxy.
Globular Star Cluster NGC 6397:
Located 7,800 light-years from Earth, NGC 6397 is the second closest globular cluster to us. Globular clusters, which contain large numbers of stars of similar age and chemical abundance, are among the oldest objects in the universe and therefore contain important evidence about the history and evolution of their host galaxy. These objects are difficult to study because it is not easy to capture the entire cluster in a single image, and also because there are so many stars in the cluster centers that the brighter ones drown out the fainter ones, making them difficult to observe. The outer regions of globular clusters extend over large distances and are home to mostly low-mass, faint stars that can provide information about previous interactions. No telescope other than Euclid can observe the entire globular cluster and distinguish the fainter stellar members in the outer regions of the globular cluster from other cosmic sources. For example, the Hubble Space Telescope observed the core of NGC 6397 in detail, but was unable to photograph the outskirts of the cluster in a single image. To study the outer regions of such clusters in detail with the Hubble Space Telescope and advanced large ground-based telescopes, it is necessary to take and examine a large number of images. Euclid, in contrast, could do this in just one hour. The Gaia satellite can measure the space motions of globular clusters, but it cannot produce data that would study their low-mass stars.
Euclid will also be used to study structures called "tidal tails" that form far away from globular clusters due to their previous interactions with the celestial island. If there are no tidal tails, there may be a halo of dark matter around the globular cluster, preventing stars in the cluster's outer region from escaping. However, a dark matter halo is not expected around small-scale groups such as globular clusters, which are cosmically small. Therefore, the discovery of tidal tails in globular clusters will provide precise determination of the clusters' orbits around the galactic centre of mass and will provide information about the distribution of dark matter in the Milky Way.
The Horsehead Nebula:
Euclid obtained panoramic and detailed images of the Horsehead Nebula, also known as part of the Orion constellation. Located about 1,375 light-years away, this Nebula is the closest to Earth among the massive star-forming regions. Although many telescopes have imaged the Horsehead Nebula, none have been as sharp as Euclid, and such a wide-area image has never been captured with a single image. With this Euclid star-forming image and similar observational data, scientists aim to search for young brown dwarves and previously undiscovered Jupiter-mass planets in our galaxy.
Ultraviolet radiation from the bright star sigma Orionis, located near the Horsehead Nebula region, causes the clouds behind the Horsehead to glow, while the thick clouds of the Horsehead block the light coming from behind. This is why the horse's head appears dark. The nebula is largely composed of molecular hydrogen, which emits very little heat and almost no light. Using detailed wide-field images of Euclid, scientists aim to study the differences in star formation conditions between the dark and bright clouds.
The first images captured by the Euclid mission reveal why we need to go into space for scientific research with the technology we have now. The first images reassure astronomers that the EUT is up to the task. Euclid can observe an area 100 times larger at a time than the James Webb Space Telescope. In addition, each of the EUT's high-resolution images contains more than 600 million pixels, allowing for clearer images of galaxies at very large distances. The structure of the large-scale cosmic web of the universe, traces of dark matter and energy, mysterious undetermined aspects of galaxies and clusters of galaxies, details of objects in deep space, and many more are the research targets of Euclid. With Euclid's data, it may be possible to see the big picture of the universe from a different cosmic perspective.
Scientists who are trying to solve the mystery of the universe and conduct research in different fields are eagerly awaiting the scientific data of the dark detective Euclid.
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