Astronomy and Astrophysics

Faculty Research Summaries | Chairman's Introduction

John Carlstrom

My research is focused on testing cosmological models of the universe. I pursue this research with new telescopes and instruments to image the intensity and polarization of the cosmic microwave background radiation, the fossil radiation from the early universe. Using our DASI telescope at the South Pole to make detailed measurements of the intensity variations and polarization of the background radiation, my research group has shown that the curvature of the universe is flat, supporting inflationary models and also providing a determination of the total density of the universe. We found that ordinary matter, the stuff of stars and us, accounts for only about 5% of the density. Another roughly 30% is composed of dark matter, presumably a yet-to -be-identified particle. Even less is known about the remaining, dominant component, the mysterious dark energy that apparently is causing the expansion of the universe to accelerate. We are building two new telescopes and detector systems to investigate the nature of dark energy by measuring its effect on the density evolution of the largest bound objects in the universe, clusters of galaxies. The Sunyaev-Zel'dovich Array (SZA) consists of eight 3.5 meter telescopes and is being deployed in California in Winter 2004. The South Pole Telescope is an 8-meter off-axis telescope to be deployed to the South Pole in November 2006.

See http://astro.uchicago.edu/dasi/

See http://astro.uchicago.edu/sza/

See http://astro.uchicago.edu/spt/

Fausto Cattaneo

My research interests are solar system astronomy and computational astrophysics.

Hsiao-Wen Chen

My research focuses on understanding the formation history of baryonic structures. I study faint galaxy statistics and cross-correlation functions between galaxies and intervening absorption-line systems identified along random lines of sight toward background quasars and gamma-ray burst afterglows.

James Cronin

(see Dept. of Physics)

Kyle Cudworth

Studies of star clusters are fundamental to several areas of modern astrophysics: stellar evolution, Galactic structure and evolution, stellar dynamics, and the calibration of the astronomical distance scale. We are using astrometric and photometric observations to obtain high precision, clean, color-magnitude diagrams for stars in globular clusters, old open clusters, and some nearby galaxies. In several cases, stellar dynamics within a cluster can be explored in detail. Distances to globular clusters are being obtained via a new method totally independent of previous techniques. Tangential velocities of distant clusters are being measured to better determine the mass distribution and formation history of the Galaxy.

Scott Dodelson

I am interested in cosmology, in particular in the broad question of how structure formed in the universe. This question is rich not only because it is fascinating in of itself, and not only because there is much data being taken that sheds light on it, but also because it touches so many issues in astrophysics and particle physics. How do galaxies form? Is there dark, non-baryonic matter? What is it? Will the universe continue to expand forever? Did the universe expand exponentially at some early phase in its history? If so, what is the particle physics responsible for this period of inflationary expansion? These are all remarkable questions; even more remarkable is the very real hope that we will be able to answer them in the coming decade. I believe there are three ways theoretical cosmologists can help answer these and other questions in the general field of structure formation. First, we can introduce new theories or models of how structure formed. This is especially important at present since one general model -- cold dark matter and its variants -- so dominates the theoretical landscape. Second, we can calculate the predictions of existing theories. Finally, we can analyze the plethora of data that is coming in and will be coming in over the next decade. I am interested in all three of these areas, find them stimulating, and hope to work in all of them in the coming years.

Joshua A. Frieman

My primary research is in cosmology, especially the formation of large-scale structure and the interplay between cosmology, particle physics, and astrophysics. Currently my research interests include the analysis of large-scale structure in galaxy surveys such as the Sloan Digital Sky Survey, the use of weak gravitational lensing observations to probe the distribution of mass on large scales, and the development of methods to probe the Dark Energy. I am a member of the Center for Cosmological Physics and of the Theoretical Astrophysics group at Fermilab, which has close connections with the cosmologists and theoretical astrophysicists at Chicago .

Michael Gladders

My research fields are cosmology and extragalactic astronomy.

Nickolay Gnedin

My research interests range from General Relativity to physics of the interstellar medium to cosmology. Right now, for most of the time I work on numerical cosmological simulations, including (but not limited to) simulating galaxy formation and evolution of the intergalactic medium. I like doing numerics and working with a computer. This often includes quite sophisticated visualization of the simulation results, so, I guess, I am a little bit a movie director as well.

Doyal A. Harper, Jr.

My research group uses infrared and submillimeter techniques to study processes related to the formation and evolution of stars, planetary systems, and galaxies. These processes proceed most rapidly in clouds of dusty gas that absorb visible and ultraviolet energy and re-emit it at far infrared wavelengths. Understanding the youngest stellar systems and most rapidly evolving galaxies depends critically on the development of infrared instrumentation that can penetrate the clouds, reveal and measure embedded sources of energy, and discover how they interact with their environment. We are currently building HAWC, a far infrared camera for NASA's Stratospheric Observatory for Infrared Astronomy (SOFIA). When the observatory is commissioned in 2005, HAWC and SOFIA will provide three times sharper images than previous far infrared telescopes, enabling new kinds of insights into how planets, stars, and galaxies are born.

Roger L. Hildebrand

(see Dept. of Physics)

L. M. Hobbs

Spectroscopic observations of the light elements lithium, beryllium, and boron in Galactic stars of all ages are being used to investigate the cosmic origin of these elements, both in the Big Bang and, in most cases, in processes that occurred much later in our Galaxy. The inferred abundances of these elements, including the two isotopic forms of lithium, provide fascinating insights into the early Universe, the chemical evolution of the Galaxy, and stellar structure. In particular, the lithium data are vitally important in empirically evaluating the properties of the Universe at a few minutes after the Big Bang.

The Hubble Space Telescope is being used to study the spectrum of the very nearby star Beta Pictoris. Strong absorption is found by gas orbiting in a solar-system-sized disk that surrounds this relatively young star; small dust particles also were previously discovered in the disk by other investigators. The time-varying gaseous absorption and the organization of the dust suggest that the disk may harbor a large number of comet-like bodies, and possibly several planets. Our current efforts are focused on detecting the faint spectral-line emission from the disk, which originates in scattering of the starlight from the parent star by the gaseous disk.

In a separate program, the Hubble Space Telescope is being used to determine the spatial distribution, motions, and physical properties of individual clouds of tenuous interstellar gas in the general neighborhood of the Sun and in the Magellanic Clouds, the nearest galaxies to our own. The combination of the HST and its high-resolution spectrograph, augmented by ground-based observations obtained at still higher spectral resolution, allows unprecedentedly precise and detailed studies of this kind.

Dan Hooper

My research focuses on the interface between particle physics and cosmology. I'm especially interested in questions about dark matter, supersymmetry, neutrinos, extra dimensions and cosmic rays.

Wayne Hu

I am a cosmological theorist and phenomenologist. My main interests center around the formation of structure in the universe and its relation to the dark side of the universe: namely the dark matter and dark energy that seems to pervade space. We are fortunate to be in a time when the data that can help answer these fundamental questions is literally flooding in. I have devoted much of my recent research to two such sources: the Cosmic Microwave Background and the weak gravitational lensing of faint galaxies. The tools needed to understand these data sets encompass both analytical and numerical elements. The former involves relativistic perturbation theory, simple radiative transfer and fluid dynamics. The latter includes cosmological simulations and data analysis.

Lam Hui

My main interests are in large scale structure, intergalactic medium, and early universe physics. I have also recently developed an interest in extra-solar planets.

Stephen M. Kent

I hold the position of Head of Survey Coordination for the Sloan Digital Sky Survey and have overall responsibility for tracking survey progress and planning observations. Additionally, I am involved in various aspects of data processing, project management, telescope optics, and commissioning the telescope and imaging instruments. My research interests are in areas of extralactic astronomy and cosmology, galaxy clusters, and near-earth objects. I am also head of the Experimental Astrophysics Group at Fermilab.

Alexei Khokhlov

My primary focus is multidimensional reactive flow fluid dynamics simulations of thermonuclear explosions of Type Ia supernovae. The results are compared with detailed observations of these events. Type Ia supernovae are used as “standard candles” for determining cosmological parameters of the universe. Understanding how these supernovae explode is very important. Explosion physics of Type Ia ’s has many analogies to terrestrial combustion and explosions.

I carry out numerical simulations of terrestrial reactive flow phenomena such as turbulent flame propagation, detonation, and deflagration-to-detonation transition (DDT). Results of simulations are used to interpret and understand combustion and detonation experiments. Physics of turbulent flames and DDT is a major challenge in a combustion theory. It is also key to building a correct model of Supernovae of Type Ia.

I am also interested in core-collapse supernovae. I am involved in designing and simulating high energy density laser experiments aimed at investigation of supersonic jets and their interaction with ambient medium. Jets may play an important role in highly asymmetric explosions of core-collapse supernovae and in gamma-ray bursts. Yet another direction of my research is numerical methods for stable integration of equations of general relativity, and adaptive mesh refinement algorithms for various types of partial differential equations.

Edward J. Kibblewhite

My current research focuses on developing new techniques to achieve diffraction-limited imaging in fully filled apertures and distributed arrays of telescopes. The full resolution of ground-based telescopes will be achieved at near infrared wavelengths using a laser beam to generate an artificial star in the sodium layer of the earth's atmosphere. This star will enable the instantaneous wavefront of the atmosphere to be measured and these data used to correct for the atmospheric distortion using adaptive optics and post processing of the images. Faint objects can be studied with a resolution of 0.05 arcsecond using the ARC telescope. The system will allow fundamentally new observations of objects from planets to distant galaxies.

Baselines of hundreds of meters are needed to study the environment and surfaces of stars or the core of active nuclei. Distributed arrays of telescopes can provide such resolutions using synthesis techniques developed in radio astronomy. Such arrays pose formidable technical and system engineering problems requiring the development of stable telescopes, precision delay lines and correlators stable to nanometers over the short observation periods. A 5- or 6-telescope array is being planned using 0.6-meter telescopes operating in the near infrared.

Edward W. Kolb

The close collaboration between the Department of Astronomy and Astrophysics and the Astrophysics effort at Fermi National Accelerator Laboratory in nearby Batavia, Illinois exploits the close ties between particle physics and cosmology/astrophysics. The major effort of my research is the attempt to understand physical processes that occurred in the very earliest moments of the "Big Bang." In these very early moments the density, energy, and pressure of the universe resembled the conditions obtained in the collisions of particles at high-energy accelerators. The microphysics of the very early universe leaves its imprint on the present large-scale structure of the universe in the form of galaxies, the baryon asymmetry, element abundances, and structure in the cosmic microwave background radiation.

Arieh Konigl

The physical processes underlying accretion and outflow phenomena in compact astronomical objects are being studied. These investigations bear directly on such issues as star formation, gamma-ray bursts, and the nature of active galactic nuclei. Since the material attracted by the gravitational pull of the compact object (be it a solar-mass protostar or a supermassive black hole) is typically rotating, it often settles into an “accretion disk” through which matter can continue to flow toward the center if there is a suitable mechanism for transporting away its angular momentum. Understanding the nature of such disks is a central research goal in view of its many potential applications. For example, in the case of protostellar disks, the structure of the accretion flow is directly relevant to the question of planet formation. Compact objects are frequently also found to give rise to energetic bipolar outflows, or jets, which propagate supersonically to large distances from the origin. In the case of gamma-ray bursts and “blazar”-type active galactic nuclei, these jets can be highly relativistic. As the outflows are believed to be powered by the accretion process, another important theoretical goal is to construct self-consistent disk/jet models and to examine their implications to the dynamical evolution of the underlying systems. The interaction of the outflows with the surrounding medium is itself of great interest and may have significant observational consequences. Magnetic fields are thought to play a key role in the transport of angular momentum within the disk, in the ejection and collimation of the outflow, and in some cases also in the emission process. They therefore figure prominently also in the theoretical effort.

Andrey Kravtsov

I am interested in how various structures we see in the Universe, from clusters and filaments of galaxies to the galaxies, black holes, and stars, form and evolve. My research involves theoretical modeling of structure formation, primarily using supercomputer simulations. I develop and analyze computer models of galaxy and galaxy cluster formation. The model predictions are tested against observations from very early epochs to the present. These tests are used to investigate the implications of various hypotheses regarding structure formation, the nature of dark matter and dark energy, as well as constraining parameters of the cosmological model that describes our Universe. I also work to develop and utilize new numerical and scientific visualization techniques.

My current research is focused on the gas dynamics simulations of galaxies and galaxy clusters. The broad questions I am working on include: (1) what is the relation between dark and luminous matter in the Universe? (2) can realistic systems with properties similar to those of observed galaxies be formed in theoretical models? (3) what determines the wide range of luminosities and morphological types of galaxies? (4) how the smallest "dwarf" galaxies form? (5) can models explain the observed scaling relations of galaxies and galaxy clusters and their evolution? (6) how stars and stellar clusters form in the context of galaxy formation and how their formation is regulated?

Richard G. Kron

Surveys of galaxies and quasars over large areas of the sky provide fundamental information about the distribution of matter up to scales as large as billions of light-years. Maps of the positions and velocities of galaxies and quasars constrain models for the evolution of density enhancements in the expanding Universe, and thus test the basic cosmological picture. The Sloan Digital Sky Survey is providing a definitive map of the relatively local Universe, and has also identified the most distant quasars, objects seen when the Universe was less than a billion year old. Such distant quasars help illuminate the state of the intergalactic gas at that cosmic epoch, and also challenge us to understand how such massive, condensed objects could have formed so early. The Sloan Digital Sky Survey is creating an enormous public database of detailed measurements of galaxies and quasars that can be mined for many other astronomical projects.

Don Q. Lamb, Jr.

My research interests cover a wide range of topics in high-energy astrophysics, including the properties of cold and hot dense matter; the structure and evolution of white dwarfs and neutron stars; X-ray emission from compact stars, especially magnetic white dwarfs; and the physics of radiation transfer in super-strong magnetic fields. My current research is focused on X-ray bursts, gamma-ray bursts, Type Ia supernovae, and galaxy clusters. My research group has also developed powerful statistical methods based on Bayesian inference, and applied them to a wide range of astrophysical problems.

Stephan Meyer

The properties of the Cosmic Microwave Background Radiation (CMBR) is one of the best observables used to constrain the models of the evolution of the early universe. We are making measurements of both the anisotropy, and the low-frequency absolute temperature of the CMBR using TopHat and WMAP. We are now developing EDGE and the SPT.

The Wilkinson Microwave Anisotropy Probe (WMAP) has measured CMBR anisotropy over the full sky. Launched on June 30, 2001, MAP is operating at the Earth-Sun Lagrange point, L2, where the earth, the sun, and the moon are nearly along a line and the instrument observes in the an area centered in the opposite direction. The first year results have shown the CMB power spectrum to be consistant with a LCDM model with 66% of the energy density being some form of dark energy. WMAP also has found evidence for a late stage of reionization with an optical depth of 0.16.

The Extragalactic Diffuse Emission Experiment (EDGE) is designed to measure the large-scale structure of the Cosmic Infrared Background Radiation (CIBR) which will provide a new probe of structure growth, galaxy and star formation, and dust emission at redshifts from z=0.5 to 2.

Richard H. Miller

Numerical experiments, carried out on self-consistent, self-gravitating systems by means of fully three-dimensional $n-$body computer programs, are the best tool available today for studies in the dynamics of galaxies, clusters of galaxies, and star clusters. Relaxation effects are suppressed by using 100,000 to a million particles. The programs continue to be extremely versatile. These experiments play the same part for galaxy dynamics as laboratory experiments do in physics. Dynamics of Galaxies is a beautiful problem in Computational Physics. Beautiful objects (galaxies and star clusters) are studied by means of a beautiful formalism (Hamiltonian mechanics).

Important discoveries have come from this work. These include, among others (1) that the nucleus of a galaxy orbits around the galaxy's mass centroid, which can cause the nucleus to appear slightly off-center or to have a velocity that differs from the rest of the galaxy by tens of km/sec, (2) that galaxies oscillate in normal modes with surprisingly large amplitudes, (3) that the strong contractions evident in galaxy collisions are normal modes of oscillation, (4) that barlike forms are dynamically preferred for rapidly rotating self-consistent stellar systems while the traditional axisymmetric disk-like form is dynamically unstable, and (5) that the gravitational N-body problem is chaotic.

Dynamical studies to study motions of a massive object (such as a supermassive black hole) near the center of a galaxy are the thrust of my recent research work. A massive object near the center of a galaxy orbits with motions like those noted in the previous paragraph for the galaxy's nucleus. Properties of those motions differ in interesting ways for different black hole masses, and we are exploring patterns in those properties. New experimental methods and techniques must be developed for each new problem, and this one is no exception. Designing and testing those methods is a challenging exercise, but new discoveries often follow.

Takeshi Oka

(see Dept. of Chemistry)

Angela V. Olinto

My work focuses on the interface between astrophysics, particle and nuclear physics, and cosmology. Over the last two decades, the combination of robust theoretical frameworks at this interface coupled with an unprecedented increase in the quality and quantity of observations over a wide range of frequencies has caused an unmatched growth in our understanding of the Universe. We have observed galaxies forming at the edge of the Universe, fine details of the relic cosmic backgrounds, and have started to narrow down the possible histories of how the Universe began. However, some major questions remain unanswered. Among the open questions, my research has focused on the origin of the highest energy particles ever observed, the origin of the magnetic fields that pervade all objects in the Universe, and the nature of the dark matter that constitutes most of the matter in the Universe.

Some subatomic particles that enter our atmosphere have so much energy that they produce a giant cascade of many tens of billions of secondary particles that can be observed by very large detectors on Earth. The particles that produce these giant air showers have been accelerated to far greater energies than can be achieved with terrestrial machines indicating incredibly powerful astronomical accelerators previously unforeseen. The explanation for the origin of these highest energy particles remains unclear. The possibility that these particles come from the edge of the observable Universe is limited by the presence of the microwave background that fills all of space and degrade the energy of such high-energy particles. The microwave background limits the location of these fantastic cosmic accelerators to relatively nearby in cosmological terms. The most plausible proposals range from supermassive black holes in centers of nearby galaxies to decaying particles left over from the Big Bang. We are searching for the answer by studying source models in detail and aspects of the propagation from source to Earth. Propagation studies are intimately related to the knowledge of magnetic fields in the largest scales presently observed and particle physics models of interactions at the highest energies. Among plausible sources, we have proposed models that range from the most nearby possibility that these particles are iron accelerated in young fast spinning neutron stars from our own Galaxy to the possible effects of large extra-dimensions on the physics of these ultra-high energy cosmic rays.

The origin of magnetic fields that pervade all objects in the Universe is also still unknown. Magnetic fields may be generated in the very early universe through processes related to phase transitions or may be a more recent phenomenon related to the formation of the first collapsed objects. We have developed models of how magnetic fields are generated and how they evolve in the beginning of the universe. We can predict the role these fields have in the evolution of protogalactic structures but direct observations of the magnetic field relics is still a great challenge. Magnetic fields trace the turbulent history of the Universe being modified by the formation and evolutions of quasars, galaxies, and clusters of galaxies. The best probe of primordial fields is the study of the present field in intergalactic space away from the largest structures. The highest energy cosmic rays provide one of the best probes of the magnetic fields in the intergalactic medium today. We are studying how magnetic fields evolve in the early universe and ways of detecting the present large scale fields that may remain from the early evolution of the Universe.

The present cosmological picture of the universe shows the dominance of a form a dark energy followed by a large contribution from non-baryonic dark matter. The dark matter may be composed of supersymmetric particles. These dark matter particles in the halo of our Galaxy can in principle be observed indirectly through the products of their annihilation. We have been studying alternative ways of detecting WIMP annihilation products in a wide range of wavelengths. This study may unravel one of the longest standing mysteries in modern cosmology.

Patrick E. Palmer

My work contains two related themes: star formation and the nature of comets. These themes are related both phenomenologically -- both involve study of cold, low density gases -- and at a deeper level -- comets provide the most pristine remaining samples of the material out of which our star, the Sun, formed.

During the spectacular apparition of comet Hale-Bopp in 1997, I participated in many collaborations using optical and radio telescopes around the world to collect data on this comet. We are still finishing up analysis and publication of this data.

One of the long-standing cometary mysteries is the origin of the CN radical, whose emission lines in cometary spectra have been identified for more that 50 years. A highly reactive molecule like CN cannot have existed in cometary ice for the age of the solar system. It must be a photo-dissociation product of a more complex, but more stable "parent" molecule. One reasonable possibility is HCN, but some have suggested that CN is produced by destruction of cometary dust. Recently, we have submitted a paper in collaboration with L. M. Woodney and Michael A'Hearn (U. of Md.), David Schleicher (Lowell Observatory), Lewis E. Snyder and J. Veal (U. of Illinois), Imke de Pater and M. Wright (U. C. Berkeley), and others in which we compared radio images of the HCN distribution obtained with the BIMA array with optical images of the CN distribution obtained at Lowell Observatory over a two week period around perihelion. We find that all data is compatible with HCN as the only parent.

In the past year, with W. Miller Goss (NRAO), I have begun several projects. These include a large area study of the star-forming region called W75, and several studies of interstellar masers.

The W75 region is very complex. There are recently formed stars, a wealth of interstellar H2O masers that are a signpost of ongoing star formation. Previous studies concentrated on a few of the most prominent maser sites and little was known about most of the area. In a series of observations over the past year, we have searched the entire area for these masers that turned up some additional masers and demonstrated how the masers sites fit with regions of dense gas and dust identified by others over the years. In addition, we observed maser emission from several transitions of interstellar OH. In particular, one of the transitions has proven to be an excellent indicator of shocked interstellar gas in supernova remnants. There are no supernova remnants in the region we observed, but there is a powerful outflow of shocked H2 molecules. Can the interaction with the H2 outflow produced the same C-type shocks that are observed in supernova remnants? We are investigating this possibility.

One of the most puzzling of the interstellar masers is H2CO. Only a few sources have been found in the Galaxy. Progress in understanding the maser mechanism is hindered by the lack of examples and because of lack of study at sufficiently fine angular scales. A few years ago, we conducted several sensitive searches but turned up no new examples. Last fall, we observed several of the known H2CO masers with the VLBA that provides sub-milli-arcsecond resolution (which corresponds to linear sizes of order the earth-sun distance at the distances of these masers). However, these observations showed that the masers are as large as 100 milli-arcseconds -- too large to provide good images with the VLBA, yet too small to resolve with the VLA. Therefore, we have proposed re-observing with the Merlin array in the UK, which when combined with the VLBA data we have will provide excellent images.

Paolo Privitera

Privitera is pursuing the challenging task of discovering the origin of ultra-high energy cosmic rays (>1019 eV). The Pierre Auger Observatory, with its 3000 km2 of effective detection area, is the largest cosmic ray detector ever built. Privitera has given major contributions in the design, construction and data analysis of the Fluorescence Detector, which observe the fluorescence light from the nitrogen molecules excited by the cosmic ray shower particles along their path in the atmosphere. The first data collected by the Auger Observatory, published in Science, are suggesting a correlation of ultra-high energy cosmic rays with nearby extragalactic astrophysical objects, opening a new field of particle astronomy.

Privitera is also leading the AIRFLY experiment for an accurate determination of the energy scale of ultra-high energy cosmic rays detected with the fluorescence technique. The spectral properties of the fluorescence emission of nitrogen molecules, as well as its pressure, temperature and humidity dependence, are being measured by AIRFLY with electron beams at several accelerators (Frascati, Argonne National Laboratory).

Clem Pryke

I am an experimental cosmologist and a member of the core team that constructed and the CMB anisotropy telescope DASI, which is sited at the South Pole. I lead the effort to set limits on cosmological parameters using the first season data, and was part of the analysis team which recently announced the long sought detection of polarization in the CMB. Currently I am working hard on the nuts and bolts of a new radio interferometry array in California, which will allow us to learn about cosmology by studying distant clusters of galaxies using the Sunyaev-Zeldovich Effect. In addition we are re-using the DASI mount as a platform for a new millimeter wave telescope called QuaD, which will make groundbreaking maps of the polarization of the CMB and should achieve the sensitivity required to detect gravitational lensing of the CMB by the intervening large scale structure.

Robert Rosner

I conduct both theoretical and (some) observational research in solar and stellar astrophysics, more general plasma astrophysics, laboratory-oriented plasma physics, and fluid dynamics, in collaboration with students, post-doctoral fellows, and faculty at the University of Chicago. This work entails both analysis and modeling of solar and stellar observations, and analytical and computational studies of both laboratory and astrophysical fluids and plasmas (especially in the context of stellar convection, stellar magnetic field generation and stellar activity). I also study the evolution and dynamics of magnetic fields in non-stellar contexts, such as in clusters of galaxies, in galaxies themselves, and in the young universe.

My recent activities have focused primarily on issues related to “combustion” and transient nucleosynthesis, as occurs in X-ray bursts, novae and Type Ia supernovae; shear flow-driven gravity wave instability and wave breaking (as applied to the problem of elemental mixing at the surface of pre-nova white dwarfs, as well as in more prosaic terrestrial circumstances); and detailed theoretical and simulation studies of the nonlinear evolution of the Rayleigh-Taylor instability. These activities are carried out under the aegis of the DOE ASCI/Alliances-supported “ Flash Center ”. We have also been focused on the development of computational tools for studying magnetic reconnection, as part of a DOE/SciDAC-funded program in this research area.

In addition, we were fortunate to learn this year that our research group, together with plasma physics groups at Princeton University's Plasma Physics Laboratory and at the Univ. of Wisconsin/Madison, won one of the coveted NSF Physics Frontier Center; this project just started this autumn (2003), and entails research related to the interaction of magnetic fields and ionized fluids in both astrophysical and terrestrial laboratory settings. Our role is to provide theoretical and computational support to this Center, with experimental efforts largely concentrated at Princeton and Wisconsin . This will be the focus of much of my own personal research over the next 5 years or so.

James Truran

The focus of my research is the attempt to understand the physical processes that are responsible for the synthesis of the heavy elements observed in nature. This necessarily involves the consideration of a broad range of problems in theoretical nuclear astrophysics. The high temperatures and densities achieved in stellar, nova and supernova environments are entirely compatible with the formation of heavy elements via nuclear processes; the sensitive dependencies of the resulting abundance patterns on the temperature, density, and convective history of the stellar matter and supernova ejecta demand that theoretical calculations of the nucleosynthesis yields must be coupled directly to hydrodynamic models of nova and supernova explosions. Many aspects of these problems are currently being studied by researchers at the ASCI/Alliances Center for Astrophysical Thermonuclear Flashes at the University of Chicago .

In order to view these studies of nucleosynthesis in individual events in perspective, it is further necessary to examination their implications for the composition of the stars and gas in galaxies as a function of time. Such studies of galactic chemical evolution are now increasingly tied to models of galactic dynamical evolution.

My current research activities include projects in the following areas: numerical simulations of thermonuclear runaways leading to nova outbursts; the consequences of hydrogen thermonuclear runaways on neutron stars (Type I x-ray bursts) for the synthesis of heavy proton-rich nuclei; r-process neutron-capture synthesis associated with supernovae or neutron star-neutron star mergers and its implications for nuclear dating of stars and star clusters; X-ray and gamma-ray emission from novae; nucleosynthesis in red giant (AGB star) environments; cosmic ray production of the light elements Li, Be, and B and galactic chemical evolution; nucleosynthesis and the observed compositions of metal deficient stars; the formation and early evolution of globular clusters; the chemical and dynamical evolution of the galactic halo; and thermonuclear reactions at high temperatures and densities.

Michael S. Turner

My research focuses on the application of modern ideas in elementary-particle theory to cosmology and astrophysics. I believe that this approach holds the key to answering the most pressing questions in cosmology. For example, there is reason to believe that the ubiquitous dark matter that holds the Universe together is elementary particles left over from the earliest moments, that the primeval inhomogeneity in the distribution of matter, which was revealed by COBE and which seeded all the structure in the Universe seen today, arose from quantum-mechanical fluctuations occurring during a very early burst of expansion called inflation, and that the existence of ordinary matter resulted from particle interactions in the early Universe that make the proton unstable and do not respect the symmetry between matter and antimatter. By testing these ideas with cosmological data, outer space becomes a window to the earliest moments of creation and to the unification of the forces and particles of Nature.

Over the next decade the search for particle dark matter, the mapping of the distribution of matter in the Universe a few hundred thousand years after the beginning through precision measurements of the cosmic microwave background radiation, and the mapping of structure in the present Universe by determining the positions of millions of galaxies should definitively test these bold ideas. Much of the crucial experimental work is being done by colleagues at Chicago ; for example, the Sloan Digital Sky Survey is mapping the positions of a million galaxies and the DASI, TopHat, WMAP, and Python experiments are measuring the fine-scale anisotropy of the cosmic microwave background radiation.

Current specific areas of research include: big-bang nucleosynthesis in era of precision cosmology; theoretical aspects of inflationary cosmology; testing the inflationary paradigm; determining the nature of the dark energy that is causing the Universe to accelerate; dark matter and dark-matter detection; dark matter and the formation of structure in the Universe; the origin of the cosmic asymmetry between matter and antimatter; understanding how to use precision measurements of the fine-scale anisotropy of the cosmic microwave background and large-scale structure to probe inflation and fundamental physics; and aspects of axion, neutrino and string cosmology.

Peter O. Vandervoort

I am particularly interested in theoretical studies of the structures and the dynamics of galaxies. My purpose is to understand the forms and internal motions of galaxies that are the consequences of the orbital motions of their constituent stars. This is accomplished through the construction of self-consistent, equilibrium models of galaxies. Stellar orbits in the prevailing gravitational fields are the "building blocks" of such models, and their study is a central part of the subject. If a galaxy in equilibrium is unstable with respect to some small perturbation, then it cannot continue to exist in that equilibrium state. Therefore, my work includes studies of the oscillations and the stability of galaxies with a view to identifying those theoretical models which can provide viable representations of real galaxies. This research makes use of methods of mathematical analysis and numerical n-body calculations.

Donald G. York

Studies of the interstellar medium and intergalactic medium are underway using Earth-orbiting and ground-based spectrographs. For gas near the Sun, absorption lines of interstellar gas in stellar spectra are used to study abundances, ionization states, phases of the medium and the make-up of interstellar grains. A major program to identify the (probably) large molecules responsible for hundreds of unidentified, interstellar absorption lines (known as Diffuse Interstellar Bands), using all of the above information, is a special focus.

Intergalactic gas, seen in absorption against background QSOs, is being used to probe and map halos of galaxies to determine the distribution of light elements that may be products of primordial nucleosynthesis, and to study the temperature, pressure, and element evolution in the gas between the galaxies. Studies of such absorption lines in spectra of distant QSOs aid in discovering high redshift galaxies, detectable in faint emission, given the redshift, using a tunable, imaging Fabry Perot system. The build-up of the elements through continuing nucleosynthesis is being used to chart galaxy evolution early in the history of the Universe.

For the next few years, the primary instruments used will be the FUSE (Far Ultraviolet Spectroscopic Explorer), to observe hot UV objects to about 14th magnitude; the ARC 3.5 meter telescope at Apache Point Observatory, with an echelle spectrograph (for DIBs), a moderate resolution spectrograph (Digital Imaging Spectrograph, for obtained redshifts of galaxies that happen to fall near background QSOs) and the Fabry-Perot imager; the 2.5 meter telescope of the Sloan Digital Sky Survey (to construct a complete atlas of intergalactic absorption lines) and to find galaxies near known QSOs; and the Hubble Space Telescope STIS spectrograph, for studies of absorption lines in galaxy halos probed by serendipitously placed, background, SDSS QSOs.