In 1924, astronomer Edwin Hubble announced a discovery that changed our perspective on our place in the universe. The Cepheid stars that he had found in the Andromeda Nebula, with which it is possible 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 that existed, but one among many.
In those same years, in which it was proven that there was a universe far beyond what was known, it was also begun to be observed that celestial bodies were not moving as expected, measuring the gravitational effect of the visible mass of stars and galaxies. Dark matter, invisible to telescopes, but which could explain these movements, had to be much more abundant than conventional matter. Now we estimate that this matter makes up 25% of the universe and that the visible matter is only 5%. The rest of the cosmos is dark energy, a hypothetical entity that causes the universe to expand faster and faster, rapidly moving the hundreds of billions of galaxies that exist away from each other.
To try to understand the nature of that 95% of the cosmos, which until now we only intuited from its effects, the probe was launched on July 1 Euclid, a detective from the dark side of the universe. Now, the European Space Agency (ESA), responsible for the mission, has made public the first five color images taken by its instruments. With them we want to show the capacity of Euclid to photograph large complete structures, from galaxies or nebulae to galaxy clusters, quickly and with high resolution, up to one third of the visible sky.
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. The study of this map will allow us to know the evolution of these objects over cosmic time and begin to understand what these two contradictory phenomena are, the dark matter that keeps large parts of the universe together and the dark matter that threatens to dilute it.
The Perseus Cluster
The image, which ESA calls a revolution for astronomy, shows 1,000 galaxies from this cluster in which there are thousands more enveloped in gas at millions of degrees of temperature. It is one of the most massive structures in the known universe and it has been shown that it could not hold together if it were not for the gravitational amalgamation of dark matter. In the background, there are 100,000 more galaxies, some so far away and so faintly bright that they have not been seen before. The shape of these galaxies appears slightly distorted in the images, because the effect of the gravity of visible objects and dark matter diverts the path of light on its journey to the Solar System. This study of billions of galaxies in the last 10 billion years of the history of the cosmos will provide a three-dimensional image of the distribution of dark matter in the universe.
The Hidden Galaxy
![Euclid](https://imagenes.elpais.com/resizer/ukA6-dELnlW7OClYUkSNdQrSXg4=/414x0/cloudfront-eu-central-1.images.arcpublishing.com/prisa/55RJKYAWZBACFE6S3UNAW2B4MQ.jpg)
The spiral galaxy IC 342, also known as a hidden galaxy because it is slightly obscured by a region of cosmic dust in our galaxy, is very similar to the Milky Way and is relatively close, about ten million light years away. The infrared camera Euclid allows us to obtain more precise information about the stars of this object, despite the dust that hides it.
Irregular Galaxy NGC 6822
![Euclid](https://imagenes.elpais.com/resizer/yonUgMQhBW15yEOLr1fwWA8JQMw=/414x0/cloudfront-eu-central-1.images.arcpublishing.com/prisa/GCT6EMBBHNCQZDKH2MOSU3PNCQ.jpg)
Euclid You will observe the brightness of galaxies 10 billion years ago, when the universe was in its infancy. Many galaxies at that time still seemed half-made, they were small and irregular and did not resemble the spirals with which we usually identify these objects. Some of these galaxies, which would later serve to form larger ones like the Milky Way, are abundant in that ancient universe, but they can also be found closer to us. This is the case of NGC 6822, photographed by Euclidwhich is located 1.6 million light years from Earth.
Globular cluster NGC 6397
![Euclid](https://imagenes.elpais.com/resizer/GBugI0sKKbb6vFIQyHJi_J7syjA=/414x0/cloudfront-eu-central-1.images.arcpublishing.com/prisa/BJEXSMWHXRHURKZ7VDZC6O4CVM.jpg)
Globular clusters are groups of hundreds of thousands of stars held together by the gravity of visible and invisible matter, forming a sphere, which are usually found in the outer halo of galaxies. According to ESA, only Euclid can observe a globular cluster at once with sufficient resolution to distinguish as many stars within the cluster. This type of grouping of stars will help us understand the distribution of dark matter
The Horsehead Nebula
![Euclid](https://imagenes.elpais.com/resizer/SqYQd0WI_prA49BmSGtNv7qp4ME=/414x0/cloudfront-eu-central-1.images.arcpublishing.com/prisa/WELVIS6YEJHKZCFGUP7I6KDAVQ.jpg)
In this hotbed of stars, one of the most iconic images of the cosmos, astronomers hope to discover unknown planets the mass of Jupiter in their infancy, and brown stars also in an early period of their development.
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