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Research in Cosmology at ASU covers the entire history of the universe, all the way from the quantum gravity epoch at the big bang, through the particle physics phase, to atomic nuclei, then to atoms, stars, galaxies, and ultimately the large-scale structure. A major focus of the Group is to connect the particle physics universe to present day observables, and to understand the transition from linear physics to the non-linear regime during the formation of structures through observational techniques. Here we summarize activities of the ASU Cosmology group.
Quantum gravity epoch
Understanding the nature of the “big bang” is at the heart of cosmology and requires synthesis of a wide variety of fundamental elements such as quantum theory, gravitational physics, particle physics and/or string theory. Further, for a theory of the big bang to be confirmed or falsified, it has to be connected to experiment and observations. Theoretical members of the group are pursuing fundamental aspects of quantum theory, gravitational and particle physics, and are tying in their models with current cosmological data. Of interest are the number of dimensions and how we can detect any extra dimensions, the energy of the vacuum (“dark energy”) and why it is so small yet still not zero, other universes, and the significance of life in our observable universe.
Particle physics epoch
Soon after the big bang, the universe is filled with a dense, hot plasma containing fundamental particles. From this primordial soup, a homogeneous universe has to emerge, antimatter has to annihilate and go away, and matter has to form protons and neutrons and the nuclei of the light elements. The light nuclei then have to combine with electrons to form atoms. Once atoms are formed, we enter the “transparent epoch” – when light can come to us from the other side of the universe. The particle physics epoch determines crucial aspects of cosmology such as the abundance of protons and neutrons, and other as yet unseen (but felt!) elements such as dark matter, neutrino background, and magnetic fields. Depending on the nature of the fundamental interactions, the particle physics epoch can lead to the presence of exotic remnants such as magnetic monopoles, cosmic strings, quark nuggets, a background of gravitational waves, and black holes. Members of the group are investigating the nature of the fundamental interactions and the consequences for terrestrial experiments and cosmological observations. They are also using observations of extreme objects such as neutron stars as probes of fundamental physics
Epoch of Reionization
Early galaxies caused the last major phase transition in the Universe approximately 1 billion years after the Big Bang as the UV and X-ray emission from their constituent stars and black holes ionized the residual primordial hydrogen gas between galaxies. ASU Cosmology Group members are leading observational programs charting the evolution of galaxies during this epoch of reionization and their influence on the intergalactic medium, and developing new techniques to enable and exploit 21 cm surveys of the intergalactic medium that will soon be available from the Murchison Widefield Array (MWA) and other radio telescopes.
Dark Ages and First Light
The cosmic Dark Ages started at recombination, the dawn of the transparent epoch, and ended during the era of First Light, when the first stars, galaxies, and black holes emerged only 200 to 500 million years after the Big Bang. During the Dark Ages, the Universe consisted almost entirely of neutral hydrogen gas (75% by mass). Members of the group are building novel low-frequency radio experiments in collaboration with colleagues around the world to detect and characterize neutral hydrogen from this period for the first time, as well as observing the progenitors of galaxies from the epoch of First Light directly with the Hubble Space Telescope and ground based optical/IR instruments.
Astrobiology
One of the distinctive properties of the universe is that it supports life. A major unsolved problem that we are tackling is whether the observed bio-friendliness of the universe is a coincidence, or evidence for a multiverse, or arises in some other way. The subject cannot be divorced from the question of the nature and origin of the laws of physics. An ultimate explanation of physical existence needs to include account of how the laws of physics arise and whether they are unique. A corollary of the fact that the universe is so well suited to life is the question of whether it is confined to Earth, or widespread in the galaxy and beyond. The answer hinges on the probability that life will emerge under earthlike conditions. One way we are investigating the problem is to seek evidence for multiple terrestrial origins of life, for example, by looking for a “shadow biosphere” of radically different microbial life intermingled with known life. If it can be established that there is more than one form of life on Earth then it is certain that the universe will be teeming with it, and the question of whether or not we are alone in the universe will take on a new urgency.
Supermassive Black Holes and Structure Growth
As galaxies grow, it is clear that massive black holes play a crucial role in their evolution by acting as central engines for a variety of extremely violent cosmic processes, some of which dominated events in the early Universe. Our members of observing unique active galactic nuclei (AGN) to understand how exactly did galaxies funnel up a significant fraction of their mass into a central supermassive object and how feedback from these objects shape the subsequent process of galaxy and star-formation, resulting in the galaxies that we see today.
Instrumentation:
Our group members are active in the design and development of the next generation of detectors and instruments for observational cosmology, from new CCD arrays for UV through near-IR imaging to radio, microwave, and THz receivers, we are pushing the state of the art in technology to expand our understanding of the evolution of the Universe and its fundamental properties.