fy2000 link to home page national science foundation

logo for the National Science FoundationNSF continued to serve as the lead Federal agency for the support of ground-based astronomy and space science, and sponsored a broad base of observational, theoretical, and laboratory research aimed at understanding the states of matter and physical processes in the solar system, our Milky Way galaxy, and the universe. NSF also supported advanced technologies and instrumentation, and optical and radio observatories that maintain state-of-the-art instrumentation and observing capabilities accessible to the community on the basis of scientific merit.

NSF-supported researchers extended their work to measure the very faint fluctuations in the microwave light emitted by the hot gas in the early universe, from a time before stars and galaxies formed. These additional data have strengthened the conclusion that the universe is nearly spatially flat and added information about the higher order peaks in the power spectrum of primordial sound waves, which have been used to estimate cosmological parameters, such as the expansion rate, the age, and the total mass of the universe, and how much of that mass is comprised of normal (baryonic) matter. Models of the universe which have a "flat" geometry are dominated by (up to 90 percent) "dark" matter and fit the standard nuclear physics models for the generation of the elements hydrogen and helium during the big bang, and have been shown to be consistent with the observations.

Researchers involved in the Sloan Digital Sky Survey discovered, in the spectrum of the most distant quasar known, the signature of neutral hydrogen in the intergalactic medium, indicating that their observations are probing redshifts before large numbers of quasars and galaxies formed. Recent observations of the highest redshift quasar yet discovered showed the signature of a high optical depth of neutral hydrogen. The existence of this neutral hydrogen indicates that in this distant epoch, the universe had not yet been flooded with a substantial density of ionizing photons from stars and quasars.

Recent radio observations of the prototypical starburst galaxy M82 revealed a complex and dynamic system. NSF-funded researchers used the Owens Valley Radio Observatory array to map the large-scale structure of molecular gas in M82. The sensitivity and area coverage of the resulting high-angular-resolution data was an order of magnitude better than previous interferometric observations. Their images showed tidal stripping of the molecular gas along the plane of the galaxy and coincident with streams of neutral hydrogen. The distribution of molecular gas also coincides with the dramatic dust features seen in optical absorption. As much as 25 percent of the total molecular mass of M82 is situated at large galactocentric radii. Researchers with the Five College Radio Astronomy Observatory used the 14-meter telescope and the focal plane array system to identify molecular gas located as high as 3 kiloparsecs above the plane of the disk of M82. Some of the carbon monoxide (CO) emission is clearly associated with neutral hydrogen tidal features that arise from the interaction of M82 with the large, neighboring spiral galaxy M81. The molecular gas in these tidal features may have been directly extracted from the molecular gas rich reservoir of M82 or formed in situ within the tidal streams.

The large, spherical halo component of our own galaxy is believed to harbor a substantial amount of unseen dark matter. NSF researchers recently observed microlensing events toward the nearby Magellanic Clouds, indicating that 10 to 50 percent of this dark matter may be in the form of very old white dwarfs, the remnants of a population of stars as old as the galaxy itself. A team of astronomers used the Cerro Tololo InterAmerican Observatory 4-meter telescope to carry out a survey to find faint, cool white dwarfs in the solar neighborhood that would be members of the halo. The survey revealed a substantial population of white dwarfs, too faint and cool to have been seen in previous surveys. The newly discovered population accounts for at least 2 percent of the dark matter, or about an order of magnitude larger than previously thought, and represents the first direct detection of galactic halo dark matter. The objects are also found in astrometric survey photographs with other telescopes, and spectra taken at the Cerro Tololo InterAmerican Observatory confirmed their white dwarf nature.

Research into the birth and the death of stars and their planetary systems continued to be an active area of investigation and discovery. Radio and infrared studies revealed protostars in the process of formation and extended structures around them that indicate preplanetary disks. Young stars at different evolutionary stages show complex outflows of wind and jets. High-resolution images of CO emission show shell structures and reveal close associations between the morphologies of CO and molecular hydrogen emission features. The CO kinematics show evidence of bow-shock interactions in a number of sources and evidence for wide-angle wind interactions. Scientists running simulations found that neither of the current popular models for stellar outflow, pure jet wind, or wide-angle wind adequately explain all morphologies and kinematics.

A major impetus to the observational and theoretical studies of the formation of stars and their planetary disks has been provided in the last few years by the discovery of extra-solar planets. NSF has supported much of this work. A recent discovery, again by the team of Marcy, Butler, Fischer, and Vogt, found a planet three-quarters the mass of Jupiter in a circular orbit around the solar-like star 47 Ursa Majoris. Although 70 extra-solar planets have been found thus far, this is the first system with two planets in circular orbits—at distances that make the planetary system similar to our own.

Brown dwarfs are cool, dim objects with masses between that of Jupiter and the Sun, so small that their cores never become hot enough to burn hydrogen into helium. Only the slow cooking of the limited amount of deuterium in the stellar interior is possible. Progress in the discovery and study of brown dwarfs has been possible through the large coordinated efforts of the 2 Micron All Sky Survey and Sloan Digital Sky Survey, both of which have been supported partly by NSF. Individual researchers have been following up these discoveries and investigating the physical properties of these new objects. Under an award in a joint NSF-NASA grants program, investigators from New Mexico State University and Washington University have developed cool cloud models appropriate to the cool, substellar temperatures found in brown dwarf atmospheres. Their new models explain the color changes seen in the spectral sequence of brown dwarfs, and their thermochemical calculations have wide application to the derivation of temperature and pressure indicators for gas giant planets, as well as brown dwarfs. Their models also predicted that large grains precipitate out of the brown dwarf atmospheres, just as rain does on Earth.

The national astronomy centers generate substantial databases and archives of observational data, often through coordinated surveys, which enable research beyond the scope of a single researcher. A recent example was the National Optical Astronomy Observatory’s Deep Wide-Field Survey, an extensive, multi-year, multicolor survey using the 4-meter telescopes at Kitt Peak and at Cerro Tololo. The first results, covering an area of 1.15 degrees square, and with it over 300,000 faint galaxies and stars, were released in January 2001. When the survey is completed in spring 2002, the full area will be 15 times this size and will provide deep images in both the visible and infrared. With it, astronomers will be able to study large-scale structures in the universe, the formation and evolution of galaxies and quasars, rare stellar populations, and the structure of the Milky Way.

Among the areas of development supported by instrumentation programs at NSF is optical interferometry, which will enable diffraction-limited imaging using aperture synthesis methods to create images from telescopes with effective apertures up to 1 kilometer in diameter. Recent results from the Infrared Stellar Interferometer, under development by Townes at UC Berkeley, show the potential of such instrumentation–measurements of nearby stars indicate that our previous understanding of stellar sizes has been confused by the dust and gas surrounding evolved stars. New measurements with ISI show stellar radii some 10 to 25 percent larger than previous measurements, changes that have implications for our models of stellar structure and atmospheres, temperature, and ultimately distance scales.

NSF continued a joint activity with the Air Force Office of Scientific Research to provide the U.S. astronomical community with access to state-of-the-art facilities at the Advanced Electro-Optical System (AEOS) telescope, in Maui, Hawaii. The capability of this 3.76-meter advanced technology telescope for scientific research is illustrated with its recent observations of Jupiter’s satellite Ganymede. Images obtained with AEOS resolve details only 270 km in size, performing significantly better than the Hubble Space Telescope.

NSF also supported technological development in the field of radio astronomy that involves the real-time adaptive cancellation of unwanted radio interference using adaptive digital filters and special signal-processing algorithms. Researchers at the National Radio Astronomy Observatory, Brigham Young University, Ohio State University, and the University of California at Berkeley have begun a program of recording high-speed data samples of signals that are known to cause interference to radio astronomical observations. With these samples in hand, tests of canceling algorithms were underway at the end of the fiscal year and have proven to be very successful for certain kinds of well-characterized and predictable signals, as in the cancellation of a signal from the GLONASS satellite.

back to top

go to nasa hqgo to nasa hq history office

Home | NASA | DoD | FAA | DoC | DoI | FCC | USDA | NSF | DoS | DoE | Smithso | Apndx | Gloss