Astronomy and Astrophysics

Astronomy and Astrophysics

Astronomers remotely study systems and phenomena beyond the Earth, normally by examining emitted, transmitted, or reflected light. Research spans space and time, from planets to stars to galaxies and aggregates thereof, from interplanetary to interstellar to intergalactic media, from the cosmic web to the Universe to the multi-verse. Most astronomers today use knowledge about physics in their attempts to understand the workings of the cosmos, and in that sense they are astrophysicists, too. Consequently, astronomical research often leads to new insights into physics, as was the case with the discoveries of dark matter and dark energy.

Here are the researchers in Astronomy and Astrophysics who are able to supervise graduate students. To see a detailed profile of anyone, including contact information, click on the title bar or portrait. To see a personal research website (if available), click on the research picture.

Supernovae and their remnants; Pulsars; Active Galactic Nuclei; Observational tests of general relativity; Radio continuum astronomy; Very Long Baseline Interferometry.

I study galactic and extragalactic compact, celestial sources of radio waves such as supernovae, pulsars, black hole candidates, radio stars and the powerful cores of radio galaxies and quasars. With the technique of very-long-baseline interferometry (VLBI) and a network of several large radio telescopes girdling the globe, it is possible to image the areas of activity of these sources and determine their positions with an angular resolution 1,000 times better than with any optical telescope on Earth. In particular, this allows us to make sequences of images of young, rapidly expanding supernovae, study the interaction of their shock fronts with the circumstellar medium, search for pulsars in their centres and compose the results in a "movie of an exploding star." As a spin-off, we obtain vital information for determining the distance to the host galaxy, which helps to anchor the extragalactic distance scale. We have developed a novel data acquisition system for phase-coherent baseband recording of pulsars to complement our VLBI observations and extend our studies to searches for new millisecond pulsars and their possible companion planets and black holes. Also, we investigate the cosmological jets of energetic particles which emanate from the active centers of so-called superluminal radio galaxies and quasars with speeds that appear to be faster than the speed of light. These studies help us to understand the physics of the immediate environment of these centres which are believed to be supermassive black holes.

Active Galactic Nuclei, especially Seyfert galaxies; Cool dwarf stars; Structure of the Milky Way galaxy.

I am interested in the nuclei of galaxies, especially the nature and origin of nuclear activity. Active Galactic Nuclei (AGN) are the centres of some galaxies which emit tremendous amounts of non-stellar radiation. Such radiation is believed to be generated by the accretion of matter -- gas and stars -- onto supermassive black holes. This intense radiation has profound effects on the circumnuclear environment of these galaxies. There are numerous members of the AGN family, including relatively nearby Seyfert galaxies and the more distant quasars. Of particular interest to me is the origin of activity in Seyfert galaxies, especially the role played by the environment in which such galaxies are situated.

I am interested also in aspects of Galactic structure, particularly M dwarf stars. The overwhelming majority of stars in the solar neighbourhood, and indeed in the Milky Way Galaxy itself, are cool, relatively unspectacular stars called late-type (M) dwarfs and subdwarfs. These stars are so faint that they cannot be seen to great distances and are consequently difficult to detect. I am involved in studying how these stars behave within the Milky Way (kinematics), as well as determining their surface temperature and metal abundance using imaging techniques.

Active Galactic Nuclei, especially quasars; Black holes; Gravitational lensing.

When matter spirals into a supermassive black hole at the centre of a galaxy, a kind of friction can heat the matter up until it shines brightly enough to be seen all the way across the universe. We call such objects quasars. I am interested in understanding more clearly the dynamics of gas spiralling around black holes in quasars. That knowledge will improve our ability to infer the physical properties of quasars and their black holes (such as mass and spin) from the details of the light they produce. I am particularly interested in outflows of gas from quasars. Much of the mass spiralling around in a quasar ends up in the black hole, but some of it is flung outwards and is sometimes visible in the spectrum of the quasar. Establishing the connections between those absorption lines and the emission lines seen in most quasars will help us understand how quasars work and how galaxies form. I am also interested in gravitational lensing, which can take a small, faint galaxy and stretch it out into a long, luminous arc. My research is both experimental and theoretical. I do much of my experimental work using online databases from large astronomical surveys, supplementing data as necessary with modern instruments on large telescopes.

Origins and diversity of planetary systems; Detection and characterizataion of exoplanets; Formation and evolution of brown dwarfs and stars.

My collaborators and I use many of the world's largest telescopes - including VLT, Subaru, Gemini and Keck - to explore the origin and diversity of planetary systems as well as the formation of stars and brown dwarfs. We also endeavour to detect and characterize exoplanets and to study the prospects for life in the universe. I also engage heavily in public outreach and the popularization of astronomy through writing, speaking, and media appearances.

Theoretical cosmology, especially cosmic inflation, eternal inflation, dark energy, and confrontations with observations; Field theory; String theory; Gravitation.

The goal of my research is to understand the fundamental laws of nature through their impact on cosmology. I am primarily a theorist, dabbling in cosmology, field theory, string theory, and gravitation. I am actively engaged in research on cosmic inflation, eternal inflation, topological defects, and models of dark energy. I also design data analysis algorithms to confront fundamental theory with observations of the Cosmic Microwave Background (CMB) radiation. Here is a sampling of the questions that drive my research: How big is the universe? What might lie beyond our observable universe, and how could we confirm or disprove various proposals? What role do the extra dimensions predicted by string theory play in cosmology? What is the fundamental nature of space-time singularities? Are there new ways of looking at cosmological datasets that could be useful when confronting theories with data? Can computer simulations of the very early universe shed light on its possible initial conditions and evolution?

Formation, evolution, and structure of galaxies; Aggregates of galaxies, especially the Local Sheet and analogues; Interstellar matter, especially gaseous nebulae.

I study the formation, evolution, and organization of galaxies large and small, with the objective of elucidating how we came to be. Insights into the mechanisms driving evolution are gained by utilizing gaseous nebulae (planetary nebulae and HII regions) to probe chemical compositions. Surface photometry, particularly at near-infrared wavelengths, is combined with dynamical measurements to seek a unified description of normal galaxies, which facilitates examination of how different kinds of galaxies are related and which ultimately confronts the “nature versus nurture” debate over origins. To refine knowledge about our place in the Cosmic Web, I implement improved methodologies for determining the distances of galaxies. A recent outcome is a precise three-dimensional map of the Local Sheet of galaxies that reveals that the development of our own galaxy, the Milky Way, was influenced by an environment of far greater extent than hitherto recognized. Now, my students and I are finding and studying analogues of the Local Sheet in the greater Universe to learn what attributes of the Local Sheet were most relevant to the realization of the Milky Way as it exists today. Modern simulations of structure formation are utilized as “virtual universes” to guide the interpretation of measurements and to test theoretical foundations. Much of the work on individual galaxies and the structures in which they are embedded also leads to insights about the origin of spin and the nature, localization, and preponderance of dark matter in the Universe. My primary research adversary is interstellar dust, and I have spent a good deal of time uncovering what lies behind it, including two hitherto unknown galaxies in the backyard of the Milky Way as well as the Council of Giants surrounding us.

Distant galaxies and clusters of galaxies; Formation and evolution of galaxies, especially environmental influences.

Most of my work is on how distant galaxies form and evolve, and how that evolution is related to their larger scale environment. Because light is redshifted by the expansion of the Universe, studies of distant galaxies almost always involve infrared observations. I use sophisticated instrumentation on ground-based and space-based telescopes to conduct multi-wavelength surveys of galaxies and galaxy clusters. In so doing, I am able to constrain star formation rates and galaxy masses as a function of redshift and thereby ascertain how galaxies grow and at what rate.

Dark matter; Physics of the weak scale; Matter/Antimatter asymmetry.

Dark matter makes up around 85% of the matter in the Universe and yet we have no explanation for it in the Standard Model of particle physics. As a particle theorist, my research focuses on proposing new ideas and new tests for dark matter in order to illuminate what this mysterious stuff actually is. Recently, I have become interested in using astronomical observations of galaxies and clusters to determine whether dark matter particles interact with each other through forces other than gravity. It is remarkable that the largest structures in the Universe, millions of light years in size, can be a laboratory to study the microscopic properties of dark matter particles. I also explore the idea that dark matter is made up of strongly-interacting constituents, much like protons and neutrons. Theories of this nature cannot be worked out using paper-and-pencil and I collaborate with lattice theorists to simulate dark matter's properties using supercomputers.