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The Laboratory
in the News

Astronomers detect echoes from ancient supernovae
A team of international astronomers has found faint visible “echoes” of three ancient supernovae by detecting centuries-old light reflected from interstellar dust clouds. Just as a sound echo can occur when sound waves bounce off a distant surface and reflect back toward the listener, a light echo can be seen when light waves traveling through space are reflected toward the viewer.
Livermore astronomer Kem Cook, a coauthor of the paper that appeared in the December 22, 2005, edition of Nature, says, “We are carrying out a large wide-field, time-domain survey looking for the signature of dark matter, and, as a bonus, we are discovering the unexpected such as these light echoes.” The light echoes were discovered by comparing images of the Large Magellanic Cloud taken years apart. By precisely subtracting the common elements in each image and analyzing which variable objects remain, the team looks for evidence of dark matter that might distort the light of stars in a transitory way.
Astronomer Armin Rest of the National Optical Astronomy Observatory, lead author of the paper, says, “Without the geometry of the light echo, we had no way of knowing just how old these supernovae were. Some relatively simple mathematics can help us answer one of the most vexing questions that astronomers ask—exactly how old is this extraterrestrial object?” Astronomers also can use supernova light echoes to measure the structure and nature of the interstellar medium. Dust and gas between the stars are invisible unless illuminated by a light source such as a supernova blast.
Contact: Kem Cook (925) 423-4634 (cook12@llnl.gov).

Cosmic dust could help uncover the origins of life
The National Aeronautics and Space Administration’s (NASA’s) Stardust spacecraft returned from a 7-year mission on January 15, 2006, bringing back cometary and interplanetary dust particles that may be able to tell the story of our solar system’s beginnings and possibly the origins of life. By tailing a comet called Wild 2 that was shooting material into space at 6.1 kilometers a second, the spacecraft captured dust particles in a collector made up of aerogel—a material consisting of 99.8 percent air.
After landing, the capsule was flown to NASA’s Johnson Space Center (JSC) in Houston and opened. Researchers from Livermore’s Institute of Geophysics and Planetary Physics (IGPP) performed some of the first extractions at JSC using ultrasonic diamond-microblade technology, which was developed at Livermore by postdoctoral researcher Hope Ishii. The first few days were devoted to optical scanning of the aerogel tiles. Extractions of particles from aerogel cells began the next week, after which samples were distributed to Livermore and other research laboratories around the world. Livermore researchers are now using the Laboratory’s transmission electron microscope—the world’s most powerful electron microscope—and the nano secondary-ion mass spectrometer to analyze the mineralogy, chemical, and isotopic composition of the dust particles.
The detailed and precise process involves carving dust tracks from the aerogel with ultrasonic diamond blades. Scientists then use microscopic needles to extract the dust from the tracks. According to John Bradley, director of Livermore’s IGPP, the actual tracks of cometary dust within the aerogel are visible to the naked eye. The particles themselves can be seen as white specks under a microscope.
Stardust is part of NASA’s series of Discovery missions and is managed by the Jet Propulsion Laboratory. Other collaborators in the project include the University of Washington, Lockheed Martin Space Systems, the Boeing Company, the Max Planck Institute for Extraterrestrial Physics, NASA Ames Research Center, and the University of Chicago.
Contact: John Bradley (925) 423-0666 (bradley33@llnl.gov).

Researchers find new way to produce coherent light
A team of researchers from Lawrence Livermore and the Massachusetts Institute of Technology found a new source of coherent optical radiation when they performed molecular dynamics simulations of shock waves propagating through crystalline sodium chloride. “To our knowledge, coherent light has never been observed from shock waves propagating through crystals because a shocked crystal is not an obvious source to look for coherent radiation,” says Evan Reed, an E. O. Lawrence postdoctoral fellow at Livermore and lead author of a paper published on January 13, 2006, in Physical Review Letters.
The simulations solved the classical equations of motion
for atoms that are subject to interaction, thermal effects, and deformation of the crystal lattice. The intensive computer simulations were made possible using Livermore’s Thunder supercomputer. Researchers expected to see only incoherent photons and sparks from the shocked crystal, but they observed weak yet measurable coherent light emerging from the crystal in the range of 1 to 100 terahertz.
Applications for these research results are numerous. For example, the coherent light produced in the crystal can serve as a diagnostic for understanding shock waves, specifically providing information about shock speed and the degree of crystallinity.
Contact: Evan Reed (925) 424-4080 (reed23@llnl.gov).

Superplastic carbon nanotubes
Researchers from Lawrence Livermore, Boston College, and the Massachusetts Institute of Technology have pioneered a new technique to stretch carbon nanotubes. A typical carbon nanotube can be stretched to 15 percent longer than its original length before it fails. In high-temperature experiments performed by the researchers, a nanotube heated to 2,000°C stretched to more than 280 percent of its original length before it broke. Carbon nanotubes are 10,000 times smaller than a human hair and are used in a variety of machines including computers, cellular phones, and personal handheld devices.
“This kind of intense stretching and reduction in diameter of
a carbon nanotube is unprecedented,” says Livermore’s Yinmin (Morris) Wang, a coauthor of the paper that appeared in the January 19, 2006, edition of Nature. The superelongation is due to a full plastic deformation that occurs at high temperatures. Under such high temperatures, the nanotube appears to be completely pliable, resulting in a superplastic deformation that would otherwise be impossible at low temperatures.
“Our surprising discovery of superplasticity in nanotubes should encourage the investigation of their mechanical and electronic behavior at high temperatures,” says Wang. “The tubes may find uses as reinforcement agents in ceramics or other nanocomposites for high-temperature applications.”
Contact: Morris Wang (925) 422-6083 (wang35@llnl.gov).

Astronomers discover distant, Earth-like planet
Using a network of telescopes scattered across the globe, an international team of astronomers has discovered an extrasolar planet that is more Earth-like than any other planet found so far. The new planet—designated OGLE-2005-BLG-290 Lb—orbits a red dwarf star five times less massive than the Sun every 10 years. The discovery opens a new chapter in the search for planets that support life. The team’s research appeared in the January 26, 2006, edition of Nature.
In most cases, new planets have been found by measuring the Doppler shift in light from the orbiting star. However, most of these planets have been giant gas planets. The team found the new rocky planet using a technique called microlensing. The planet is not directly “seen,” nor is the star that it’s orbiting, but its presence can be deduced from the effect of the planet’s gravity on light from more distant stars. “There’s a deviation of light when a planet is in the way,” says Kem Cook, an astronomer at Lawrence Livermore who is also a member of PLANET (Probing Lensing Anomalies NETwork), a part of the group that made the discovery. “In this instance, there was a half-day brightening that was indicative of a planet.”
Microlensing can show just how common planets are in distant parts of the galaxy and probe details of planetary formation that other techniques cannot. The discovery of the Earth-like planet is the joint effort of three independent microlensing campaigns: PLANET/RoboNet, the Optical Gravitational Lensing Experiment, and Microlensing Observations in Astrophysics. The effort involves 73 collaborators affiliated with 32 institutions in 12 countries.
Contact: Kem Cook (925) 423-4634 (cook12@llnl.gov).

A quantum leap in materials modeling
A Livermore team has determined the solid–liquid and solid–solid phase boundaries of carbon for pressures up to 20 million Earth atmospheres and more than 10,000 kelvins. “Results of computer simulations show a consistent description of elemental carbon in a broad range of temperatures and pressures,” says Alfredo Correa, a University of California (UC) at Berkeley student who works in Livermore’s Physics and Advanced Technologies Directorate under the Student Employee Graduate Research Fellowship Program. The physical properties of carbon are of great importance for devising models of Neptune, Uranus, white dwarf stars, and extrasolar carbon-rich planets.
In its elemental form, carbon is found in materials such as coal, graphite, diamond, bucky balls, and nanotubes. These materials have very different properties, but, at the microscopic level, they differ only in their carbon atoms’ geometric arrangements. Experimental data on the phase boundaries and melting properties of elemental carbon are scarce because of difficulties in reaching megabar (one million atmospheres) pressures and temperature regimes of thousands of kelvins in the laboratory.
“Our simulation results call for a partial revision of current planetary models, especially for the description of their core regions,” Correa said. “Our computational work also may help us interpret future experimental work.” Correa is the lead author of a report published in the January 31, 2006, online edition of the Proceedings of the National Academy of Sciences. The research team is composed of Correa, Stanimir Bonev, and Giulia Galli, all of whom were at Livermore at the time the work began. Galli is now a professor at UC Davis, and Bonev is an assistant professor at Dalhousie University in Canada.
Contact: Alfredo Correa (925) 422-3520 (correatedesco1@llnl.gov).

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UCRL-52000-06-4 | April 12, 2006