In 1924, astronomer Edwin Hubble announced a discovery that changed the way we view our place in the universe. The Cepheid stars he found in the Andromeda Nebula, which can be used to measure immense cosmic distances, showed that it was not a nearby cloud of gas and dust, but a galaxy like ours at an enormous distance. The Milky Way was not the only galaxy in existence, but one of many.
In the same years that it was proven that there was a universe far beyond what was previously known, it also began to be observed that celestial bodies were not moving as expected, which measures the gravitational effect of the visible mass of stars and galaxies. Dark matter, which is invisible to telescopes but could explain these movements, had to be much more common than conventional matter. Now we estimate that this matter makes up 25% of the universe and that visible matter makes up only 5%. The rest of the cosmos is made up of dark energy, a hypothetical entity that is causing the universe to expand ever faster, rapidly pushing the hundreds of billions of galaxies in existence apart from each other.
To try to understand the nature of this 95% of the cosmos, which until now we have only been able to guess from its effects, the Euclid probe, a detective of the dark side of the universe, was launched on July 1st. Now the European Space Agency (ESA), which is responsible for the mission, has released the first five color images taken by its instruments. The aim is to demonstrate Euclid’s ability to photograph large complete structures, from galaxies or nebulae to clusters of galaxies, quickly and at high resolution up to a third of the visible sky.
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Over the next six years, it will observe the distances, shapes and movements of hundreds of billions of galaxies to create a three-dimensional map of the universe that will reach objects up to 10 billion light-years away. Studying this map will allow us to understand the evolution of these objects over cosmic time and to understand what these two contradictory phenomena are: the dark matter that holds large parts of the universe together and the dark matter that binds it to threatens to dilute.
The Perseus Cluster
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The image, which ESA is calling a revolution for astronomy, shows 1,000 galaxies from this cluster, where there are thousands more enveloped in gas with a temperature of several million degrees. It is one of the most massive structures in the known universe and has been shown to be unable to hold together without the gravitational fusion of dark matter. In the background are 100,000 more galaxies, some so distant and so faintly bright that they have never been seen before. The shape of these galaxies appears slightly distorted in the images because the effects of gravity from visible objects and dark matter redirect the path of light on its journey to the solar system. This study of billions of galaxies over the last 10 billion years of cosmic history will provide a three-dimensional picture of the distribution of dark matter in the universe.
The hidden galaxy
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The spiral galaxy IC 342, also called the hidden galaxy because it is easily obscured by a region of cosmic dust in our galaxy, is very similar to the Milky Way and relatively close, about ten million light-years away. Euclid’s infrared camera allows us to obtain more precise information about this object’s stars, despite the dust that hides it.
Irregular galaxy NGC 6822
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Euclid will observe the brightness of galaxies 10 billion years ago, when the universe was in its infancy. Many galaxies at the time appeared half-finished; they were small and irregular and did not resemble the spirals we typically use to identify these objects. Some of these galaxies, which later formed larger galaxies like the Milky Way, are abundant in this ancient universe but can also be found closer to us. This is the case of NGC 6822, photographed by Euclid, located 1.6 million light-years from Earth.
Globular cluster NGC 6397
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Globular clusters are groups of hundreds of thousands of stars bound together into a sphere by the gravity of visible and invisible matter and are usually found in the outer halo of galaxies. According to ESA, only Euclid can observe a globular cluster at the same time with enough resolution to distinguish as many stars within the cluster. This way of grouping stars will help us understand the distribution of dark matter
The Horsehead Nebula
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In this hotbed of stars, one of the most iconic images of the cosmos, astronomers hope to discover unknown planets with the mass of Jupiter in their infancy and brown stars also early in their evolution.
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