On July 1, 2023, the Euclid Space Telescope was launched on a Falcon 9 rocket. It has now reached its destination: orbit around the sun 1.5 million kilometers from Earth, alongside NASA’s flagship James Webb Telescope.
Euclid had enough time to open his lens to space and begin his mission: to find numbers and place them on the invisible dark mass and dark energy of space.
Over the course of six years, the space telescope will photograph a third of the sky and take pictures of one and a half billion galaxies.
Analysis of the numerous images will show how dark forces influenced the form and content of the universe.
Perhaps Euclid will revolutionize not only our understanding of dark matter and dark energy, but also the fundamental theories of cosmology.
These observations could confirm our understanding of gravity and the history of the universe, or force scientists to rethink everything.
Dark matter accelerates stars
Galaxies are gathered into large groups, called galaxy clusters. Already in the 1930s, observations showed that galaxies in these clusters revolve around each other faster than can be explained by the stars we see.
Swiss astronomer Fritz Zwicky, who analyzed this phenomenon, believed that there must be mass in galaxies that we do not see. This mass is called dark matter (in German). Dark matter).
Dark matter causes stars in the galaxy to orbit around the galactic center faster than they would otherwise.
In the 1970s, American astronomer Vera Rubin measured the rotation of a number of galaxies. It was then clear that galaxies contain more than five times the amount of dark matter as ordinary matter.
Since then, physicists have been trying to figure out what dark matter actually is.
We still only know that dark matter does not emit, reflect or absorb light, and that it can pass through ordinary matter without making any noise.
Every second, billions of dark matter particles can pass through our bodies without us noticing.
In hundreds of experiments, physicists have tried to make dark matter reveal its presence, but so far it has left no trace, other than that it attracts ordinary matter with its gravity.
Dark matter’s gravity caused ordinary matter to aggregate into giant cosmic structures. Galaxies lie like dewdrops on a three-dimensional spider’s web, where the threads are dark matter.
Now the Euclid Telescope will map this matter.
Using the Euclid telescope, astronomers will be able to create a three-dimensional picture of the universe.
The image can be compared to images that doctors obtain using computed tomography machines.
In the 3D image, researchers can see how galaxies have assembled over the past 10 billion years. This allows them to learn how dark matter shaped the universe.
In addition, researchers will take advantage of a phenomenon called weak gravitational lensing to detect dark matter. The effect gets its name from the fact that dark matter, like ordinary matter, bends the space around it so that light from distant galaxies bends and makes its way through the universe before it reaches us.
Dark matter thus acts as a kind of lens that makes galaxies appear slightly distorted when their light reaches Euclid’s telescope.
Analyzes of distorted galaxies could bring scientists closer to the truth about dark matter.
Scientists don’t yet know exactly what matter is made of, but two candidate particles have been put forward: relatively heavy particles called wimpar.Macromolecules interact weaklyWeakly interacting massive particles) and lighter particles, called axons.
Euclid’s observations can be compared with the computational models of wimpers and axes, thus showing researchers the way towards the correct conclusion.
The universe is accelerating
The universe is expanding. Researchers have already proven this in the 1920s. The galaxies are getting further and further apart, because the space between them is increasing, something that can be measured.
Astronomers have actually predicted that the expansion will slow slowly but surely because of the matter in the universe, because all matter attracts all other matter through its gravitational pull.
Instead, in 1998 scientists came to the exciting conclusion that the expansion is not only continuing, but accelerating. Therefore, there must be energy that counters the gathering force of gravity and “pushes outward.” It was called dark energy.
In the simplest model, dark energy is built up in space itself and acts as a repulsive force, i.e. negative pressure, that causes space to expand.
More space means more dark energy, which gives extra space and so on.
But maybe dark energy isn’t that simple.
Light from distant galaxies is bent by dark matter, so it appears distorted from our perspective. Scientists working on the Euclid Telescope can use this anomaly to map dark matter and measure how dark energy causes the expansion of the universe.
1. Distant galaxies emit light
Euclid’s camera records light emanating from one and a half billion galaxies in the universe ten billion light-years away. Hence the light of the galaxies comes from a relatively early period in the 13.8 billion year history of the universe.
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2. Dark matter bends light
On the long journey through the universe, light from galaxies encounters clumps of dark matter that bend space around it. Light follows curved space and changes direction on its way toward us.
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3. Dark energy has spread into dark matter
Analyzes of galaxy shapes tell astrophysicists how much dark matter is in the universe and how it clumps together. This data also helps calculate the impact of dark energy on the universe.
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© Ken Ikeda Madsen/Shutterstock
Using Euclid, scientists can figure out how fast galaxies have moved away from each other over the past 10 billion years.
This way, they can find out whether dark energy always behaves the same way everywhere in the universe. It is likely that the strength of dark energy varies over time. Then physicists will have to find a new model for the universe and its evolution.
Theories may need to be rewritten
Euclid is the only space telescope that focuses solely on the dark universe. But the measurements that the telescope will make will not be the only ones, because scientists are in the process of building the large American Vera C. Rubin Observatory.
It will stand on top of Mount Cerro Pachón in northern Chile, and in 2024 it will begin photographing the skies over the Southern Hemisphere.
In addition, NASA’s next large space telescope, the Nancy Grace Roman Space Telescope, will launch in 2027. It will be twice the size of Euclid and will be able to see farther into space.
Together, Euclid, Rubin, and Roman can provide more accurate calculations and help us understand dark energy.
The big question is whether astrophysicists’ best model of the universe holds up.
Physicists build their model of the universe on two assumptions: first, that the matter in the universe is evenly distributed, and second, that the universe appears to be the same in all directions, and that it is also expanding at equal speed in all directions.
If Euclid’s measurements show that this is not the case — for example, if the universe is expanding faster in one direction than in the other — physicists will have to go back to the drawing board.
It would be a big surprise if Einstein’s theory of general relativity turned out to be wrong.
Then researchers need to come up with a completely new theory of gravity.
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