The new European telescope will examine the dark parts of the universe

95% of the universe is made up of something we don’t know much about, which is dark matter and dark energy. Both affect the structure, growth, and distribution of things we can see in space, but they neither emit nor absorb light.

To try to find answers to some of the biggest questions in cosmology, the Euclid Space Telescope was created. Euclid was built by the European Space Agency (ESA) with assistance from NASA. The work involved 21 countries and cost about 1.4 billion euros.

The postponement takes place on Saturday 1 July 17:11 Swedish timeIf canceled, the European Space Agency has another chance to get the telescope into space the next day.

– What Euclid will do is a large, deep 3D map of the structure of the universe. The telescope will map and take pictures of the starry sky and is expected to be able to identify about a billion and a half galaxies. It would be like a movie about how the universe has evolved over ten billion years, says Martin Sahlin, a lecturer in astronomy with an emphasis in astrophysics at Uppsala University.

Dark energy is associated with the expansion of the universe

The universe is expanding, and at an increasing speed. Dark energy is driving the accelerating expansion, which he doesn’t know exactly. Martin Sahlén explains that there are two main ways to explore dark energy. Partly by examining the expansion of the universe, and partly by seeing how it happens when large structures appear.

Many measurements of the expansion have been made, but with the help of Euclid’s mapping, researchers will gain additional information about dark energy with the largest mapping yet of how galactic structures evolved from today to about ten billion years ago.

The hope is that we will be able to see if the properties of dark energy change over time in any way. So far, its properties seem to be constant over time, but if it detects some kind of change over time, it would be a huge step forward in understanding the paths we need to take to understand fundamental physics, says Martin Sahlin.

There are many theories about what dark energy is. An exotic particle or gravitational effect that might behave differently in separate regions are two possible suggestions. If you think of the universe as a large network of galaxies, with some regions containing more galaxies and others sparse, then it is precisely this network that needs to be investigated.

Galaxy clusters are knots in the cosmic fabric. When filaments of galaxies cross each other, you have a galaxy cluster. We’re talking about orders of magnitude of ten megaparsecs and up, says Martin Sahlin.

Parsec is a unit of length used in astronomy and corresponds to approximately 3.26 light-years. Therefore, it is the giant structures that must be investigated.

Einstein’s “biggest mistake” can be crossed out

If the researchers see in their measurements that the properties of dark energy are different today than they were many years ago, it would change parts of our understanding of physics.

– Then we can delete the cosmological constant, which is the Standard Model we have today. It works, says Martin Sahelin, but we don’t have a clear understanding of what it is.

The cosmological constant is a cosmological quantity introduced by Albert Einstein as part of his general theory of relativity. He himself called it his “biggest mistake”, but today the constant is important in many cosmological models.

The cosmological constant is a measure of the amount of dark energy and the amount of energy. But if it changes over time and is not constant, then there is a chance that there is some new physics that we need to understand. This constant is a bit difficult for us to understand theoretically, why it has its value and to some extent why it exists at all, says Martin Sahlin.

Maps can be combined with other notes

Martin Sahlin is interested not only in the big drawing to be done, but also in seeing the results of Euclid’s observations of very early galaxies.

– you’re partly making very large mappings, and partly also observations of three smaller regions in the sky as you go back about 13 to 13.5 billion years in time. We expect to find at least thousands, with good luck up to hundreds of thousands of galaxies, that existed until the universe was about a billion years old, he says.

The search for really early galaxies will be the largest yet. The James Webb and Hubble space telescopes have done mapping in the past, but with Euclid you get significantly better statistics. Especially for the largest and rarest galaxies, according to Martin Sahlin. These galaxies are difficult to detect with James Webb, but once found, they can be studied in detail with a telescope to understand their physics.

– During the formation of galaxies, dark matter gathers together into halos, like large clouds, and inside them ordinary matter also gathers, leading to the formation of stars and galaxies. Exactly when these processes began in the early Universe, and how big the first galaxies were, we don’t know everything yet, says Martin Sahlin.

The measurements from Euclid will also be combined with future radio observations from the Square Kilometer Array telescope, which, among others, the Onsala Space Observatory is helping to develop and in which Uppsala and Stockholm universities are also involved, says Martin Sahlin.

Radio measurements map the hydrogen gas that surrounded early galaxies, which also fueled star formation. But when the first stars light up, the hydrogen begins to ionize, so step by step the gas goes from being neutral to being fully ionized. By combining radio measurements of hydrogen gas with maps of the galaxy from Euclid, one can understand how it is connected. It would also be able to provide information about how dark matter functioned in the early universe, as well as whether there was some form of early dark energy, says Martin Sahlin.

Below you can follow the live broadcast from the postponement, broadcasting begins at 16:30 on Saturday 1 July.