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DARK MATTER AND DARK ENERGY

The biggest mystery that recent observations have revealed is that most of the matter in our universe is not like the matter that we are made of. Unlike or own matter, most matter in the universe - in our galaxy even - neither absorbs nor emits light. It thus has been called "dark matter". Evidence for the existence of dark matter keeps on mounting. We can infer the presence and distribution of dark matter from its gravitational pull, but nobody yet knows what its microscopic properties are. Most likely, it is made up of so far undetected particles. To successfully detect and identify these particles, a theoretical understanding of how they interact is necessary and this is one of the main research avenues pursued at Nordita.

We also know today that the universe is nearly spatially flat, and continues to expand with an ever increasing speed. Within the framework of Einstein's theory of General Relativity this can only be explained by the presence of a peculiar type of energy that has been called "dark energy". We only know that this dark energy must have a negative pressure and be smoothly distributed throughout the universe. In its simplest incarnation, the density of dark energy is also constant in time, in which case it corresponds to the "cosmological constant" that was first introduced, and then again discarded, by Einstein himself. In the more general case, the density of dark energy can also change with time. Whether or not it does cannot be extracted from presently available data, but it may soon be possible.

Nordita's researchers have made significant contributions to understanding the cosmological dark sector and continue to push ahead on solving these mysteries. Former Nordita Director Katherine Freese has put forward influential proposals for both direct and indirect detection of dark matter particles, and she pioneered now widely used computational methods in the field, such as the interaction rates for different types of particles that dark matter might be made of.

The underlying theoretical framework and the prospects of eventually experimentally identifying dark matter are studied at Nordita in collaboration with the nearby Oskar Klein Center. In this collaboration also investigations into the nature of dark energy are carried out. If dark energy is not just a cosmological constant this would have observational consequences: Dark energy then might be able to interact with dark matter or even with normal matter, and so could be discovered in forthcoming experiments - provided that experimentalists know what to look for. A particularly powerful probe for this is the structure of filaments formed by galaxies and galaxy clusters, which will be measured by the Euclid satellite to an unprecedented accuracy. Two of the current Nordita members are also involved in the Euclid consortium.


This page was printed on 2024-03-29 from www.nordita.org/research/he/dm