Chairman's Introduction, Michael Turner | Faculty Research Summaries

Research in astronomy and astrophysics at the University of Chicago covers a broad range of topics, including the Sun and solar-like stars, cosmic rays, the chemical origin of meteorites and comets, interstellar matter, the birth of stars, the death of stars and nucleosynthesis, high energy and relativistic astrophysics, the origins and dynamics of galaxies, and cosmology. The activities involve theoretical, experimental, and observational programs among a community of faculty members from the Departments of Astronomy and Astrophysics, Chemistry, Geophysical Sciences, Mathematics, and Physics, with connections to Argonne National Laboratory and Fermi National Accelerator Laboratory.

The students and faculty of the University of Chicago enjoy access to a wide range of observational facilities. The Departmental observational facility is a 3.5-meter aperture telescope located on Sacramento Peak in New Mexico. This telescope has been designed to permit routine remote observing and rapid changeover between instruments, and is instrumented to work from 0.35 mm to 2 microns. A very high resolution Echelle Spectrograph built by a team led by faculty member Roger Hildebrand has just been commissioned. It will allow Chicago researchers to determine the composition of stars nearby and to probe the Universe at a time before stars and galaxies existed. Adaptive optics are being developed for the telescope, which will enable faint objects to be studied with a resolution of 0.1 arcsecond; this program is part of a larger NSF-funded effort at Chicago to bring a variety of adaptive-optics techniques to bear on improving the image quality of large-aperture reflecting telescopes. The instrumentation and the adaptive optics are being developed both at the Chicago campus and at the Yerkes Observatory, located in Williams Bay, Wisconsin. Yerkes Observatory serves as a laboratory for development of the instruments and techniques to be used on major telescopes, including the 3.5-meter telescope, the Stratospheric Observatory for Infrared Astronomy (SOFIA), and the Infrared Telescope Facility. Yerkes also provides a continuing observational program, with its famous 40-inch (1-meter) refractor and its 41-inch (1-meter) and 0.6-meter reflectors.

In addition, Chicago astronomers regularly use telescopes at the national observatories (Kitt Peak National Observatory and the Cerro Tololo Inter-American Observatory), as well as at other observatories such as the CSO, JCMT, Keck I and II and UKIRT facilities on Mauna Kea, telescopes of the McDonald Observatory in Texas, the 200-inch Hale telescope at Palomar, and the Very Large Array (VLA), BIMA and OVRO radio arrays. Various active NASA satellites (and archives) are also used, including IRAS, Einstein, EXOSAT, IUE, HST, ROSAT, COBE, Compton GRO, Rossi XTE, and EUVE, as well as high-altitude balloons. Chicago astronomers will soon participate in observatories that are coming into operation, including the SubMillimeter Array (SMA), SOFIA, the Chandra X-ray Observatory, HETE-2, and the Gemini 8-meter telescopes.

In particular, John Carlstrom's interferometry program at the BIMA and OVRO facilities has produced some spectacular results. Using the BIMA and OVRO arrays outfitted with his group's receivers, he has used the Sunyaev-Zel'dovich (SZ) effect to image more than 30 clusters of galaxies. (The SZ effect is a small spectral distortion of the cosmic microwave background [CMB] caused by the scattering of the CMB photons by the hot ionized gas bound to galaxy clusters.) From these measurements, they have been able to measure the expansion rate of the Universe (Hubble constant) and determine the total amount of matter in the Universe. Carlstrom and his collaborations have also used the OVRO array to study the role of magnetic fields in the formation of nearby, young, solar-like stars and their protoplanetary disks.

The University of Chicago is the lead institution in the Center for Astrophysics in Antarctica (CARA). CARA is an NSF Science and Technology Center (STC) that began in February 1991. The center supports several astrophysical experiments: AST/RO - The Antarctic Submillimeter Telescope and Remote Observatory, which is a 1.7-M off-axis instrument optimized for use from 1 mm to 300 microns to study star forming regions in our Galaxy and external galaxies; VIPER, a 2-meter telescope optimized to observe the anisotropy of the CMBR on angular scales between 6 arcminutes and 1 degree; Abu, a 1024 x 1024 element detector array sensitive from 3 to 5 microns; DASI (Degree Angular Scale Interferometer), an interferometric CMBR anisotropy experiment designed to study 20% of sky on angular scales from 6 arcminutes to 1 degree.

Chicago, together with Fermilab, Princeton University, the Institute for Advanced Study, Johns Hopkins University, a consortium of Japanese institutions, the US Naval Observatory, the Max-Planck-Institute for Astronomy and the University of Washington, have built a 2.5-meter dedicated telescope, a half-billion-pixel CCD camera, and a 600-object spectrograph to study the large-scale structure of the Universe. The main scientific goals of the Sloan Digital Sky Survey are to construct a three-dimensional map of the Universe by obtaining redshifts for a million galaxies and 100,000 QSOs and accurate digital five-color photometry for 200 million objects. The six-year survey began in January 1999, and the first science results (e.g., three of the four highest redshift quasars and the first methane dwarf star) have recently been published. The 30-terabyte SDSS database will soon become the largest and most important astronomical database in existence.

The infrastructure for computing -- important for both observational and theoretical work -- is also very strong at Chicago. Computing facilities for theoretical and numerical work have recently been expanded in the area of visualization, as part of a major NASA-supported initiative in high-performance computing and communications. Much of the campus pioneering of computer networks, graphics, workstations, and telecommunications have been done in the Department. The Department enjoys a close working relationship with the Argonne National Laboratory (ANL) in the area of computing; ANL is a Federal laboratory managed by the University of Chicago for DOE, which has a particularly strong program in high-performance parallel computing.

The Department is also the principal host of the Center for Astrophysical Thermonuclear Flashes ("Flash Center"), and is led by Robert Rosner, professor in Astronomy and Astrophysics. This Center is one of five university-based centers of excellence funded by the DOE Accelerated Strategic Computing Initiative (ASCI) program, and represents a large collaboration between some 35 University scientists, representing almost all of the PSD's departments and institutes, and scientists at the University-managed Argonne National Laboratory, at Rensselaer Polytechnic Institute, and at the three DOE defense programs laboratories. The primary focus of the Center is to develop a new generation of computational tools for attacking the problem of nuclear burning on the surfaces of neutron stars and white dwarfs, and in the interior of white dwarfs (in the latter case, such burning results in Type Ia supernovae). This development involves creation of new tools for computing on massively parallel computers; new algorithms for following the complex fluid behavior of astrophysical nuclear flames; and new methods for storing and displaying the resulting data.

The study of astronomical objects by researchers at Chicago begins nearby, with the solar system. Our proximity to the Sun allows detailed studies of this, the nearest star. Studies of active regions provide clues to the nature and origin of its magnetic field, and numerical simulations of turbulent compressible convection help us to understand the nature of energy, angular momentum, and magnetic field transport in the outer layers of this star; and tools of helioseismology, together with theory, are being used to probe the interior of the Sun. Observations of other, solar-like, stars are then used by Chicago scientists as a means by which ideas developed in the solar context can be tested: such stars thus become our laboratory.

The appearance of a truly great comet, comet Hale-Bopp, in 1997, provided an opportunity of a lifetime to study a truly primitive sample of the solar system (more accurately, of three lifetimes). Faculty member Patrick Palmer participated in a number of collaborations using optical and radio telescopes around the world to collect data. Analysis is still in progress, but the results have already yielded a much more complete view of the composition of comets.

The atomic nuclei that make up cosmic rays are the only sample of matter directly available from distant stars. Observations to determine the isotopic abundances of cosmic rays are carried out in the Laboratory for Astrophysics and Space Physics, giving information on the origin of cosmic rays, and, by implication, on conditions within exploding supernovae, flare stars, solar flares, etc. Cosmic ray instruments designed and built in the Laboratory have reached the edge of the solar system aboard Pioneer 10, and orbited the Earth on the space shuttle's Spacelab II.

Meteorite fragments often contain material in a state that is little changed from the conditions within the solar nebula that gave rise to the present Sun and planets. Precise determination of their chemical and isotopic abundances reveals their age and the conditions under which they were congealed. Microscopic diamonds from beyond the solar system have recently been discovered in fragments of meteorites analyzed in the Enrico Fermi Institute.

Stars and gas clouds are part of a continuing cosmic cycle: Gas clouds collapse into molecular clouds, eventually form stars shrouded in dust, and finally shine through the clouds as normal stars. When the stars die, some of their matter returns to space to form more clouds. Research at Chicago covers all phases of this cycle and involves close collaboration between theorists and observers.

Interstellar clouds are monitors of the history of element evolution. Recent work on abundances has changed our views about how grains of dust must be formed. Molecular clouds are regularly studied to understand the complex chemistry, and the magnetic field structure, of these coldest-of-all regions of space. The mass range of stars that can be detected has been greatly enlarged by new techniques developed at Chicago.

Detailed models of stellar evolution near the end of a star's life have given us new understandings of the precursor stages of supernovae, including such dramatic events as novae. Theoretical research on nucleosynthesis --- the formation of heavy elements in the interiors of these stars --- benefits from close contact with chemical and isotopic studies of meteorites and cosmic rays.

Research in high-energy and relativistic astrophysics ranges from the astrophysics of white dwarfs, neutron stars, and black holes, including accretion-powered pulsars and the transient phenomena of intense X-ray and gamma-ray bursts, to the high energy emission and jets associated with the nuclei of active galaxies. Detailed studies of properties of spinning black holes, and the purely mathematical properties of the gravitational field equations, are also active areas of research at Chicago.

Numerical simulations have emerged as one of the most powerful tools of theoretical astrophysics --- such calculations can be viewed as the theoretician's equivalent of laboratory experiments, which help us to understand the functioning of complex, generally highly non-linear, astrophysical systems. Chicago has traditionally been a leader in this area, including in the area of galaxy dynamics (where one of the aims is to better understand theoretical models of galaxy oscillations and instabilities), stellar evolution, and fundamental astrophysical fluid dynamics.

One of the main areas in which such theoretical studies closely connect to observations is in studies of cosmic magnetic fields, in which Chicago has played a dominant role. The properties of magnetic fields in the cosmos, the origin of those fields, and their continual activity pose a theoretical problem of long standing. Infrared polarimeters designed and built in the Department have led to new discoveries about the topology of magnetic fields in regions of star formation, and in the Galactic center. Recent work has shown that there is a close connection between the topology of magnetic fields and their activity: the role played by the formation of singular regions in magnetized gases in plasma heating and activity has been a major focus of study at Chicago. This work has direct observational implications, especially for studies of the X-ray emissions from the Sun and other similar stars.

In the past few years, progress has been made in understanding the very early history of the Universe (earlier than one hundredth of a second). This understanding has come about through synergistic efforts between astrophysicists and particle physicists, who have applied to cosmology such recent ideas in particle theory as grand unified theories, gauge theories, supersymmetry/supergravity, and superstring theories. It now appears that the explanations for some of the most important aspects of the Universe that we see today, such as its smoothness and flatness, the origin of galaxies and large-scale structure, and the asymmetry between matter and antimatter, can be traced to events, which occurred during the earliest moments of the Universe. The Department has played a leading role in developing this new field. In this work, the cosmology group on campus works closely with the Fermilab Theoretical Astrophysics Group, whose main focus is particle physics and cosmology.

Cosmology is entering a new phase where the bold ideas born of deep connections between the inner space of the elementary particles and the deep outer space of the Universe today are being tested by observations. Observers and experimenters at Chicago are playing a leading role in this effort. Projects include the Sloan Digital Sky Survey, participation in the DEEP Survey (using the Keck telescopes) to probe the evolution of galaxies, Carlstrom's use of the SZ effect to image distant galaxy clusters, and several experiments to measure the anisotropy of the CMB to probe the Universe at an earlier and simpler time.

Faculty member Meyer is involved in two CMB experiments, MAP and TopHat. The MAP satellite, scheduled to fly in December 2000, will measure the CMB anisotropy over the full sky in five frequency bands from 22 to 100 GHz. The angular resolution of the highest frequency is 12 arcminutes. The TopHat experiment is a balloon-borne experiment designed to measure 5% of the sky in a region around the south celestial pole. The bolometric instrument has five channels sensitive to frequencies from 150 to 600 GHz. TopHat is scheduled to fly in late December 1999 or January 2000 and nicely complements MAP. The third CMB experiment is John Carlstrom's interferometer (DASI), which will be deployed at the South Pole in December 1999. Beyond its anisotropy capability, which will be significant, it holds the promise of eventually making important measurements of polarization.

One hundred years ago we did not know how stars work and knew of only one galaxy. We can now trace the history of the Universe back to within a fraction of the beginning as well as tracing stars from birth to death. We are asking deep questions about how the Universe began, how stars explode, the origin of the chemical elements and the interworkings of black holes. The confluence of advances in our understanding of the Universe and leaps in technological capability have astrophysics poised for many exciting decades as the next millennium dawns. Our Department is well prepared to participate in this most important and exciting endeavor.

Michael Turner, Chairman

Faculty Research Summaries