in the News
Analysis of interplanetary dust yields clues
Using a transmission electron microscope, Laboratory researchers have detected a 2,175-angstrom extinction feature (or bump) in interstellar grains embedded within interplanetary dust particles (IDPs). They identified organic carbon and amorphous silica-rich material as the carriers of the 2,175-angstrom bump. This discovery may help explain how some IDPs formed from interstellar materials. The team’s research is presented in the January 14, 2005, edition of Science.
The carbon and silicate grains may have been produced by irradiation of dust in the interstellar medium. The measurements may help explain how interstellar organic matter was incorporated into the solar system. “Our finding potentially breaks a log-jam in the search for the carrier of the astronomical 2,175-angstrom bump,” says John Bradley, director of Livermore’s Institute for Geophysics and Planetary Physics (IGPP) and lead author of the paper. “Over the past 40 years, a variety of exotic materials have been proposed. Our findings suggest that organic carbonaceous matter and silicates, the ‘common stuff’ of interstellar space, may be responsible for the 2,175-angstrom bump.”
The Livermore work was funded by the Laboratory Directed Research and Development (LDRD) Program. Other collaborators on the project include researchers from the University of California at Davis, Lawrence Berkeley National Laboratory, Washington University, and the National Aeronautics and Space Administration’s Ames Research Center.
Contact: John Bradley (925) 423-0666 (firstname.lastname@example.org).
Tibetan tectonic fault linked to recent tsunami
Laboratory researchers along with colleagues in France and China have determined that the Karakorum Fault in Tibet, a feature formed by the same tectonic “collision” that caused the tsunami on December 26, 2004, in Asia, has slipped 10 millimeters per year during the last 140,000 years.
Scientists Rick Ryerson of IGPP, Bob Finkel of the Energy and Environment Directorate, and Marie-Luce Chevalier (a visiting student from the Institut de Physique du Globe de Paris) studied Karakorum movement along a single strand of the fault system over a millennial time scale and found the slip to be 10 times larger than previous data have shown.
The researchers measured the mid- to late-Pleistocene (from 2 million to 11,000 years ago) slip rate on the southern stretch of the fault by dating two moraine crests displaced by the fault at the end of the Manikala glacial valley. (A moraine is an accumulation of boulders, stones, or other debris carried and deposited by a glacier.) The dating method is based on the accumulation of isotopes produced when cosmic rays hit Earth’s surface. The researchers found that the moraines become younger from east to west, which is consistent with the right-lateral motion on the fault.
“Determining the past and present movement along the Karakorum Fault is crucial in understanding the movement of the entire Asian continent,” Ryerson says. “It’s the collision of the India continental material and the Asian continental material that has caused the uplift of the Himalayas and Tibet.” The research, conducted under LDRD funding, appears in the January 21, 2005, edition of Science.
Contact: Rick Ryerson (925) 422-6170 (email@example.com).
Banner year for the JASPER gas gun
Fifteen successful shots were fired with the JASPER two-stage gas gun at the Nevada Test Site (NTS) in 2004. An experiment on December 14 was the eighth plutonium shot for the year, the eleventh plutonium experiment in the series, and the thirty-eighth shot since the gas gun became operational in March 2001. For the December 14 shot, the JASPER team used a bullet to create the first isentropic compression on a plutonium sample. The method used a new Livermore-developed impactor technology, allowing the JASPER team to investigate plutonium at pressures and densities previously inaccessible to experimentalists.
Mark Martinez, test director, characterizes the gas gun’s capabilities as unique. “Shots cost significantly less than a subcritical experiment while providing the very best equation-of-state data over a wide range of relevant conditions,” he says.
Chief scientist Neil Holmes heads JASPER’s shock-physics experiments that study how materials—especially plutonium—behave as a shock wave passes through them. Holmes explains, “Specifically, JASPER’s main goal is to measure plutonium’s EOS [equation of state].” EOS is the relationship between the pressure, density, and temperature of plutonium at extreme conditions that encompass millions of atmospheres of pressure and temperatures up to thousands of kelvins. JASPER uses shock waves generated by high-velocity impacts to achieve these extreme conditions.
According to Holmes, acquiring plutonium EOS data is a crucial requirement in stockpile stewardship. The JASPER EOS results complement shock-physics data produced by the ongoing subcritical experiments at NTS and experiments at the National Ignition Facility at Livermore.
Contact: Mark Martinez (925) 423-7572 (firstname.lastname@example.org).
Researchers gain insight into galaxy formation
Observations using the Very Large Array at the National Radio Astronomy Observatory in New Mexico, the Keck telescopes in Hawaii, and the Hubble Space Telescope, have shown astronomers Wil van Breugel and Steve Croft of IGPP that Minkowski’s Object, a peculiar starburst system in the NGC 541 radio galaxy, formed when a radio jet was emitted from a black hole and collided with dense gas.
The researchers carried out the observations after computer simulations performed by Livermore’s Chris Fragile, Peter Anninos, and Stephen Murray showed that jets—undetectable in visible light but revealed by radio observations—may trigger the collapse of interstellar clouds and induce star formation. Van Breugel says, “It brings poetic justice to black holes because we think of them as sucking things in, but we’ve shown that when a jet emits from a black hole, it can bring new life by collapsing clouds and creating stars.”
Radio jets are formed when material falls into massive black holes. Magnetic fields around the black holes accelerate electrons to almost the speed of light. These electrons are then propelled out in narrow jets and radiate at radio frequencies because of their motion in the magnetic fields. The jets may affect the formation of stars when they collide with dense gas. But only recently have van Breugel and Croft determined how this happens.
The region between stars in a galaxy, commonly called the interstellar medium, is filled mainly with gas and dust. The gas appears primarily in two forms: as cold clouds of atomic or molecular hydrogen, or as hot ionized hydrogen near young stars. The Livermore researchers observed that when a radio jet ran into a hot, dense hydrogen medium in NGC 541, the medium started to cool down and formed a large neutral hydrogen cloud and, in turn, triggered star formation. Although the cloud did not emit visible radiation, it was detected by its radio-frequency emission.
Other collaborators included the University of California at Davis and Santa Barbara, Columbia University, ASTRON of The Netherlands, and Australian National University.
Contact: Wil van Breugel (925) 422-7195 (email@example.com).