Collaborative Research: A Comprehensive Theoretical Study of Cosmic Magnetic Fields, their Origin, Evolution, and Signatures

点击翻译按钮获取中文摘要

People use a compass to learn their direction of travel. Such a compass works because its tiny magnetic needle aligns with the magnetic field of Earth and indicates the direction of North. On scales much larger than Earth, our own Milky Way Galaxy also has its own magnetic field. In fact, all galaxies in the Universe appear to have magnetic fields, and these magnetic fields can have profound effects on a galaxy's development throughout its lifetime. Through a series of sophisticated computer simulations, this project aims to unlock the puzzling origin of the magnetic fields found in galaxies. Upon completion this project might point to an origin of these magnetic fields that coincides with the birth of the Universe itself. Such a result could have a profound influence on our current understanding of fundamental physics, and its pursuit serves the national interest of developing US scientific leadership in astrophysics. This project will also strengthen the US science workforce by directly training undergraduate and graduate students in general and computational astrophysics. Project plans also include a vigorous education and public outreach program.More technically, observations show that galaxies have magnetic fields with a component that is coherent over a large fraction of the galaxy with field strengths of order microgauss. These fields are assumed to be from the amplification of initial weak seed magnetic fields of unknown nature. The two scenarios of their origin are (1) a bottom-up astrophysical one, where the needed seed field is generated on smaller scales and (2) a top-down cosmological scenario where the seed field is generated prior to galaxy formation in the early Universe on scales that are large now. Based on current observations, this project aims to distinguish between these two scenarios. To achieve this goal, the evolution and observational signatures of cosmic magnetic fields will be studied in different astrophysical environments such as clusters, galaxies, and interstellar medium. Numerical simulations will model the evolution of cosmic magnetic fields in the expanding Universe with time varying dissipative properties when initial conditions correspond to the different scenarios of the magnetogenesis. This project is divided into the following related parts: (i) theoretical studies of magnetogenesis mechanisms including the cosmological and astrophysical scenarios; (ii) numerical simulations of large-scale magnetic fields evolution to analyze whether astrophysical mechanisms can lead to extragalactic magnetic field strengths comparable with the lower bounds; and (iii) determining potentially observable signatures of cosmic magnetic fields coherent at large scales---including cosmic structure formation, microwave background fluctuations, or ultra high energy gamma-ray propagation. The project will search for signatures of primordial cosmic magnetic fields that distinguish cosmological seeds from astrophysical sources.