Dark Universe

One of the most important discoveries of the past 50 years in physics and astronomy, is that there is much more to the universe that meets the eye: the universe appears to be permeated by mysterious forms of matter and energy, that shape the universe and determine its structure and evolution.

According to modern cosmology, only 5% of the matter and energy budget of the universe is made of the same form of matter that we see all around us -- which as we know is made of atoms. The remaining 95% is referred to as the ‘dark universe’.

Caption: According to modern cosmology, a web of dark matter permeates the universe, and supports all cosmic structures. In this snapshot taken from the Illustris Simulation, we see on the left the dark matter density, and on the right the density of gas in a massive cluster of galaxies. Source: Illustris Project

We don’t know much about this dark side of of the universe, but if we look at the matter-energy budget of the universe today, we can confidently say that on very large scales 25% appears to be composed of an unknown form of matter, known as dark matter, and another 70% behaves like a sort of repulsive gravity, that pushes the universe to expand ever faster, and is generically referred to as dark energy.

Caption: Visualization of the history of the Universe. In order to make sense of the structure and evolution of the universe, we need to postulate the existence of dark matter and dark energy. Source: NASA/WMAP Science Team

These are not mere conjectures: the Nobel Prize in Physics was awarded in 2011 to Saul Perlmutter, Brian Schmidt and Adam Riess, for the discovery of the accelerated expansion of the universe, and in 2019 (for one half) to Jim Peebles, for theoretical discoveries in cosmology, including his pioneering work on dark matter.

The existence of dark matter has long been suspected, and at GRAPPA we actually study the fascinating history of this elusive component of the universe (Bertone, van Dongen). But it was only in the 1970s that different lines of evidence merged within the framework of the rising field of physical cosmology, and provided convincing evidence for a form of matter that is fundamentally different from anything we have ever observed in our laboratories, or with our powerful telescopes.

Researchers at GRAPPA try to identify the nature of dark matter with a variety of approaches: we devise strategies to detect high-energy radiation produced by dark matter (Ando, Bertone, Weniger), we set up methods for detecting dark matter ‘clumps’ with gravitational lenses and stellar streams (Ando, Bertone, Weniger), and we explore the new opportunities arising from the booming field of gravitational waves (Baumann, Bertone, Weniger).

Our group is also active in the field of dark energy, with GRAPPA researchers pioneering a new method to determine the expansion rate of the universe, based again on gravitational waves (Nissanke).