Galactic Dynamics

Dark Matter

The existence of a relevant amount of invisible matter inside the galaxies was first postulated nearly a century ago, when the astronomers discovered that they rotated more rapidly than what could be explained by the visible mass only. It is now widely accepted that most of the matter in the Universe is in the form of an elusive substance which does not emit nor absorbs light, and thus remains undetectable by observation with any telescope. This peculiar property led scientists to call it with the generic name of “dark matter”. So far, its presence has been revealed only by the gravitational force that it exerts. Despite so many decades of extensive investigations, the nature of the dark matter is still poorly known. Recent theories indicated some kind of exotic particles (called WIMPS) as the best candidates of constituting the dark matter in the Universe. Many experiments are currently ongoing aimed to the direct detection of these particles by means of their rare interaction with ordinary matter, but they all have so far failed to collect any clear evidence. Our own Galaxy is not an exception, and its fast rotation reveals the presence of a relevant quantity of dark matter in it, but its distribution and its density in the solar neighborhood is still known mainly from models and theories, with very scarce observational measurements available. This is very unfortunate because the dark matter, being the dominant component of the Universe, plays a crucial role in the process of formation and evolutions of all galaxies, including ours. Dark matter exerts a gravitational force on the stars inside the Galaxy, and thus affects their movement as they orbit around the Galactic center. The amount of dark matter in the solar vicinity can thus be evidences studying in detail the motion and the spatial distribution of a large quantity of stars, and applying the fundamental equations of the galactic dynamics. These measurements require an extensive observational effort, often prohibitive in the past decades, and they are now made possible to unprecedented detail by the modern extensive surveys, which are collecting a huge amount of data easily accessible to the scientific community.

Faculty member active in this area: Christian Moni Bidin