Cosmology

Andrew Hamilton wants to determine the exact curvature of space, the structure of dark matter, the nature of dark energy, the origin of chemical elements, conditions that give rise to galaxy clusters, and the history of the universe concealed within variations of the cosmic microwave background. He also wants to know more about the origins of quasars and the formation of the universe's first stars and galaxies more than 13 billion years ago. Hamilton and his colleagues recently began a study of the structures formed by ordinary matter and dark matter about 12.7 billion years ago, soon after the first stars had appeared and the Universe became transparent to light. In their simulation, ordinary matter formed filaments connecting the largest galaxies. These filaments may have functioned as “superhighways” for accreting gas onto galaxies to fuel star formation. In contrast, dark matter was concentrated into globular shapes located somewhat irregularly along the filaments of ordinary matter. The researchers are now investigating the mechanism responsible for this marked separation of dark and ordinary matter.

Understanding dark matter's role in the distribution of galaxies in the universe is a central question in cosmology. Using a supercomputer simulation of the formation of the first stars and galaxies, Hamilton's group modeled the gravitational collapse of exotic dark matter and the creation of gaseous filamentary structures (a cosmic web) that attracted hydrogen and helium gases, initiating star and galaxy creation. The model used single galaxies, each with an attached halo, as the fundamental objects for study, making it easier to compare observations with theoretical predictions. With it, the researchers have been better able to explain the relationship between the distribution of galaxies and the distribution of dark matter in galaxy haloes.

Hamilton and other astrophysicists analyze huge amounts of data from space-based observatories to find clues to help them answer questions posed by cosmologists. Thus far, research findings support the following features of cosmology's Standard Model: (1) the universe is spatially flat; (2) about 70% of the universe consists of dark energy that is causing an accelerated expansion of the universe; (3) more than a fourth of the universe is made from cold, dark matter, possibly consisting of massive particles hundreds of times larger than a proton; (4) about 4% of the universe is made from baryonic matter, which comprises the atoms and molecules that make up people and the familiar objects of our world; and (5) the rest of the universe consists of neutrinos and cosmic microwave background radiation.