fy2000 link to home page national science foundation

logo for the National Science FoundationAfter extensive data analysis, an international team of cosmologists led by Andrew Lange of the California Institute of Technolgoy and Paolo de Bernadis of the University of Rome released the first results from the BOOMERanG (Balloon Observations Of Millimetric Extragalactic Radiation and Geomagnetics) Antarctic long-duration balloon flight that took place during FY 1999. The measurements provide the first truly convincing observational evidence that is consistent with the leading “inflationary” theories of creation.

“Cosmic shear” is defined as slight distortions in the images of distant galaxies caused by large intervening structures of primarily dark matter. During FY 2000, J. Anthony Tyson and his colleagues detected a statistical signal of cosmic shear for the first time, using wide-field images with the NSF Cerro Tololo Inter-American Observatory 4-meter telescope. This initial detection was based upon measurements of the images of about 50,000 galaxies. These measurements provide a powerful tool to determine fundamental cosmological parameters related to the distribution of mass in the universe and test the foundations of cosmology.

John Dickey of the University of Minnesota is midway through an NSF-sponsored 4-year project to carry out a survey of radio emission in the inner Milky Way using radio-wavelength telescopes in Australia. The survey is producing maps of the density and velocity distribution of interstellar hydrogen gas. These maps trace out the violent motions of the interstellar medium associated with supernova remnants and stellar winds. The first survey results have revealed several very large-scale structures, including an immense shell or bubble more than 1,500 light years in diameter. This supershell, located in the outer galaxy, at about 33,000 light years from the Galactic center, is the largest and most empty supershell yet discovered in the Milky Way.

Alyssa Goodman of Harvard University has produced important results in another NSF-sponsored project that offers quantitative new measures of how material in the interstellar medium is distributed. She has been developing and applying new methods for analyzing both numerical simulations and observed data sets. With these new, discriminating statistical techniques, she and collaborators have shown that simulations without magnetic fields and/or self-gravity cannot match the behavior exhibited by real observations. Only simulations of magnetized, self-gravitating turbulence are able to approach matching the behavior of the real star-forming interstellar medium. Self-gravity means that one has to include the effects of the gravitational field of the material in the interstellar medium upon itself. That is, each molecule and grain in the interstellar medium has a gravitational field that interacts on every other molecule and grain in the medium. The total effect cannot be ignored if one wishes to obtain results that agree with real observations.

Among the most active areas of research and discovery in astronomy today are investigations into the birth and the death of stars and their planetary systems. Searches for extrasolar planets have become increasingly productive recently, and samples have grown from a few curiosities to data sets whose properties and characteristics can be analyzed for insight into common formation processes. Several groups have been extremely active and productive in the search for extrasolar planetary systems. Using high-precision radial velocity measurements of candidate stars, investigators have been monitoring the presence of planets by regular changes in velocity, as the star and planet revolve around a common center of gravity. Common center of gravity means that if one were to place oneself above the plane of the orbit of the planet around the star, and traced the path that the planet made, one would find that both the planet and the star appear to orbit a common point, known as the “center of gravity.”

NSF-sponsored researchers Paul Butler of the Carnegie Institute of Washington; Geoffrey Marcy of the University of California, Berkeley; and Steve Vogt of the University of California, Santa Cruz and collaborators have found 30 of 44 known extrasolar planets. Their most recent work includes the first optical detection of a planet as it passed in front of its host star and the discovery of the first multiple planet system.

Observations show that flattened disks of gas and dust are common around young stars. Several of the stars known to have giant gas planets also have disks, believed to be the remnants of the nebulae from which the planets formed. Peter Bodenheimer and collaborators at the University of California, Santa Cruz, have been performing numerical simulations of the interactions between protoplanets and disks. They find that once a planet grows to about Jupiter’s mass, a gap is created in the disk. If two giant planets form, each one opens up a gap. Ultimately, the inner planet is driven outward slightly, and the outer one tends to be driven inward. These models are beginning to provide a theoretical basis for understanding the unusual properties of the extrasolar planets, such as their close proximity to their stars, and their high orbital eccentricities.

Fragmentation of molecular cloud cores, during their self-gravitational collapse to form stars, is the leading explanation for the origin of binary and multiple protostars. Molecular cloud cores appear to be supported against collapse in large part by magnetic fields. However, most protostellar fragmentation calculations have either ignored the effects of magnetic fields or found that in the presence of frozen-in magnetic fields, fragmentation is prohibited.

Alan Boss of the Carnegie Institute of Washington and collaborators have computed the first three-dimensional calculations that show magnetic tension also helps in avoiding a central density singularity during protostellar collapse. The net effect is to enhance fragmentation of collapsing magnetic cloud cores into multiple protostar systems.

During the approximately 15-billion-year lifetime of our Milky Way galaxy, several billion supernova explosions have progressively enriched it with the oxygen that we breathe, the iron in our blood cells, the calcium in our bones, and the silicon in the soil at our feet. Supernova explosions, with a peak luminosity as high as an entire galaxy of stars, trigger the births of new stars, are the source of the energetic cosmic-rays that irradiate us on Earth, and collectively may have helped shape the earliest galaxies. In addition, supernova have recently been used to measure the geometry of the universe and implicated as a potential source of gamma-ray bursts.

Modeling supernova has proven problematic: most models collapse, but do not explode. What material is initially ejected when the supernova detonates tends to fall back onto the stellar core. Adam Burrows of the University of Arizona and collaborators have developed a time-dependent, spherically symmetric code for modeling supernova explosions and have applied it to the problem of supernova in binary star systems. Explosions of massive stars in binary systems and the velocity “kicks” that the component stars receive are believed to be the origin of some of the high velocities seen in pulsars.

Because of its direct impact on terrestrial life, understanding how the Sun works has a very high scientific priority. NSF-sponsored researchers Douglas Braun of the Solar Physics Research Corporation and Charles Lindsey of Northwest Research Associates obtained the first images of an active region on the far side of the Sun using seismic holography techniques. Active regions are the centers of energetic phenomena such as solar flares and coronal mass ejections whose occasional bursts of radiation interfere with telecommunications and power transmissions on Earth and can pose significant hazards to astronauts and spacecraft.

William Merline and colleagues at the Southwest Research Institute have used ground-based adaptive optics to search for satellites orbiting asteroids. The team has discovered a satellite around the asteroid 45 Eugenia. The main asteroid’s diameter is close to 215 km, and the Moon’s size is estimated to be 13 km in diameter. The Moon is 285 times fainter than the main asteroid and is very close to the main asteroid (just over 5 asteroid diameters away).

Jens Gundlach and Stephen Merkowitz of the University of Washington have made an important new determination of one of the fundamental constants of nature, the gravitational constant. Their value for the gravitational constant is a hundred times more precise than the previously accepted value.

Detailed model studies for thermonuclear explosions on the surface of an accreting neutron star have been performed by the research groups of Hendrik Schatz of Michigan Statue University, Michael Wiescher of the University of Notre Dame, and Lars Bildsten of the Universtiy of California, Santa Barbara. The results defined for the first time the endpoint for the process that drives the thermonuclear explosion and sets new limits on the resulting abundance distribution in the crust of the neutron star.

During large magnetic storms, the electric fields and particle populations, which typically occur at high latitudes in the auroral region, move toward the equator, and their effects can be observed over the continental United States. Intense convection electric fields cause the plasma in the ionosphere to move at high speeds, which can cause density variations in the ionosphere that can disrupt transionospheric communication and navigation signals. John Foster of the Massachuessetts Institute of Technology, using the Millstone Hill incoherent scatter radar near Boston, observed such a disturbance during the magnetic storm of October 15, 1999. Scientists have been using these detailed radar and optical observations to test quantitatively their understanding about the relationship between these various atmospheric phenomena. By connecting ionospheric phenomena to magnetospheric processes, scientists will better understand the coupled space weather environment and will be able to improve forecasts of magnetic storms and the resulting effects on technological systems.

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