It is now widely recognized that Coronal Mass Ejections (CME) on the Sun are responsible for the most dramatic effects on Earth's atmosphere. Enabled by NSF support, recent progress has been made in understanding the relationship between CME's and regions of high solar wind flow that rotate with the solar atmosphere. Scientists have isolated specific changes to the Sun's magnetic field that result in CME's, a result that gives hope for eventually predicting the occurrence of these explosions. Scientists have successfully employed advanced modeling, using observations of the solar magnetic field as input, in determining the three dimensional flow of solar wind plasma away from the Sun.
NSF researchers have also made progress in modeling the response of the magnetosphere to variable solar wind input. A new modeling technique called Hall Magnetohydrodynamics has been successful in modeling the critical role of magnetic reconnection in initiating the explosive auroral phenomenon known as a substorm. Scientists have made significant progress in assimilating observational data into models of the magnetosphere and ionosphere, which allows improved determination of important space weather effects such as the transport of energetic particles in the radiation belts and the three dimensional configuration of electric fields and currents in Earth's ionosphere produced by substorms.
Atmospheric studies have concentrated on the middle atmosphere, an altitude region that traditionally has been difficult to observe. New measurement techniques involving radars, lidars, and passive optical instruments have revealed a rich variety of phenomena manifesting the combined processes of chemistry and dynamics. Noctilucent clouds, often referred to as the harbingers of global change, have been studied extensively to identify the temperature and atmosphere composition that give rise to ice crystals in the polar mesosphere. Unique, high-power lidar observations from the Starfire Optical Range near Albuquerque, New Mexico, have produced measurements of wave activity in the middle atmosphere with unprecedented time and spatial resolution. This facility was also used to probe long duration atmospheric contrails created during the Leonid meteor shower in November 1998.
Spread F is a phenomenon in the ionosphere responsible for disruptions to navigation and communications signals at middle and low latitudes. Spread F has been observed recently using combined optical and radar observations from facilities in Puerto Rico and Peru. New radar techniques now enable the separation of temporal and spatial variations to better understand the origin of these irregularities. The role of electric fields and neutral winds in the atmosphere has been evaluated in the structure and evolution of Spread F.
Researchers working under support provided by the NSF have furthered our understanding of star formation in galaxies, learning that the fragmentation of a protostellar cloud early in its collapsing phase seems to work best as a mode of formation for long-period binaries that are widely spaced. Joel Tohline and his associates at Louisiana State University have found that instabilities in the cloud can lead to fission. They have been experimenting with visualizing the mass transfer in interacting binary systems. A self-gravitating rotating protostellar cloud of gas and dust becomes more oblate, deforms into a dumbbell shape, and then divides into a protobinary system. This work was featured in the April-June 1999 issue of EnVision.
The Sun is the only star for which we can resolve surface details sufficiently well to provide precise constraints on stellar modeling techniques. Because its activity has a direct impact on terrestrial life, understanding the Sun is a very high scientific priority. With NSF support, Robert Stein has modeled the processes by which energy leaves the Sun's interior, manifests itself as material plume-like flow known as convection, and excites acoustic vibrations that are detectable at the solar photosphere. The models constructed by Stein of Michigan State University, Douglas Braun of the Solar Physics Research Corporation, and other solar astronomers have achieved an unprecedented level of agreement with observations.
Jim Hernstein and his colleagues at the NSF-supported National Radio Astronomy Observatory have used the Very Large Baseline Array (VLBA) to make measurements of water emission from the central regions of the galaxy NGC 4258. The measurements yielded a direct measurement of the distance to this object, about 23.5 million light-years. This result differs significantly from the inferred distance of about 28 million light-years obtained by astronomers using the Hubble Space Telescope. There may be previously unrecognized systematic errors in the Hubble distance scale for the universe.
On April 14, 1999, Geoffrey Marcy of San Francisco State University announced the discovery of three planets around the star Upsilon Andromedae. This is the first time that multiple planets have been discovered around a single star outside the solar system. One of the planets is about three-quarters the mass of Jupiter, and the others are about twice and four times Jupiter's mass.
NSF-supported research has identified the oldest, most distant galaxy found to date. Kenneth Lanzetta of the State University of New York at Stony Brook analyzed data from the Hubble Space Telescope and the Very Large Telescope to find this galaxy. The probable redshift of the galaxy is 6.68. This remarkable achievement was announced on April 14, 1999, and the results were published in Nature. Because it has taken billions of years for the light from this galaxy to reach us, the galaxy is being seen as it existed 1 billion years after the Big Bang.
Francois Roddier of the University of Hawaii demonstrated diffraction-limited performance with the NSF-supported Gemini-North 8-meter telescope, using a 36-element curvature-sensing system operating in the near-infrared region of the spectrum. Images of several astrophysical objects were obtained with a resolution of 0.07 arc-seconds. For comparison, the resolution of the Hubble Space Telescope in the same spectral region is approximately 0.15 arc-seconds.
James Stone of the University of Maryland, with Jim Pringle of Princeton University and Mitch Begelman of the University of Colorado, has performed direct numerical magnetohydrodynamic simulations of accretion flows onto black holes. They find that strong convective motions (turbulence) dominate the flow in the inner regions, resulting in a mass inflow rate strongly dependent upon distance. Surprisingly, inflow is everywhere nearly exactly balanced by outflow. The net mass accretion rate is a small fraction of the rate at which mass is supplied from large radii.
support has enabled studies of the evolution of massive stars. Edward
Baron of the University of Oklahoma, Peter Hauschildt of the University
of Georgia, and Stanford Woosley of the University of California at Santa
Cruz have developed realistic theoretical models for several classes of
normal and peculiar supernovae. Their new grid of model atmospheres provides
a crucial basis for ascertaining whether observations of Type Ia supernovae
(SNe Ia) really imply an accelerating universe, as suggested by the Principal
Investigator and others, or whether the physical properties of supernovae
have evolved since the Big Bang. These models directly confront the observations
by predicting the likely spectral evolution of SNe Ia and indirectly by
helping to determine the ages of the oldest stars, providing an independent
check on the age of the galaxy. For a few minutes, a gamma-ray burst radiates
more light than everything else in the universe. Very recently, Baron,
Woosley, and University of California at Santa Cruz graduate student Andrew
MacFayden have extended their research to the possible connection between
supernovae and gamma-ray bursts. These two groups have proposed that similar
explosion mechanisms and observational selection may account for the similarities
seen in supernovae and gamma-ray burst events.