The Formation of Dark Matter Structures in the Universe
Risa H. Wechsler, Stanford University

Numerous observations indicate that nearly 90% of the mass in the Universe is an unobserved substance called "dark matter". Although it has yet to be detected directly, dark matter's influence can be seen through its gravitational effects. These effects appear in the internal dynamics of galaxies, motions of galaxies in clusters, and the evolution of the entire Universe. Dark matter's key feature is that it does not interact electromagnetically, meaning that it can't be seen with telescopes. However, its large-scale effects are relatively easy to understand because they depend entirely on gravity.

Cosmologists can simulate the evolution of the Universe, beginning with estimations of the structure of the Universe that we believe existed at just a few hundred thousand years after the Big Bang. This structure can be evolved forward in time using numerical simulations of gravity's effect on dark matter. These simulations indicate that dark matter quickly clumps into bound objects known as dark matter halos, which provide the seeds for galaxy formation and can also be used to trace the expansion history of the Universe.

Most scientists think that dark matter is a subatomic particle, but its identity and properties (including its mass and interaction mechanisms) are still unknown. The details of how structure forms on both small and large scales provide clues into what dark matter may be. I will discuss how measurements of structure formation can help us identify the nature of dark matter.