In November 2013, after nearly a decade of work by an international collaboration, the Gemini Planet Imager (GPI) began collecting light from planets outside our solar system. GPI (pronounced gee-pie) is the first astronomical camera designed to directly detect light from extrasolar planets (exoplanets) or dusty disks that are 1 million to 10 million times fainter than the stars they orbit. The GPI team, which includes researchers from Lawrence Livermore, released the first images at the January 2014 meeting of the American Astronomical Society.
“These early first-light images are almost a factor of 10 better than the previous generation of instruments,” says Livermore astrophysicist Bruce Macintosh, who led the collaboration under the direction of the Gemini Observatory. “In one minute, we were seeing planets that used to take us an hour to detect.”
About the size of a small car, GPI is deployed on the 8-meter-diameter Gemini South telescope near the summit of Cerro Pachón in Chile. The imager’s sophisticated adaptive optics (AO) system is designed to eliminate the blurring effects caused by turbulence in Earth’s atmosphere. The AO system has a 2-centimeter-square deformable mirror with 4,000 actuators that correct for atmospheric distortions by adjusting the mirror’s shape 1,000 times per second with an accuracy of better than 1 nanometer. Manufacturing the mirror with etched silicon instead of reflective glass reduced its size and improved its stability.
“GPI’s performance requirements are extremely challenging,” says Livermore engineer Lisa Poyneer, who developed algorithms and led testing for the AO system. “As a result, the system features several original technologies that were designed specifically for exoplanet science.”
For the first-light observations, the GPI team targeted previously known planetary systems, including the four-planet HR8799 system and Beta Pictoris. The researchers also operated the imager in polarization mode, which is tuned to look at starlight scattered by tiny particles, allowing them to study a ring of dust orbiting the very young star HR4796. Previous instruments could detect only the edges of this dust ring, which may be the debris remaining from planet formation, but GPI can follow the ring’s entire circumference.
Imaging exoplanets complements other astronomical projects, such as NASA’s Kepler Mission. Former Livermore postdoctoral researcher Dmitry Savransky, who worked on GPI before moving to a position at Cornell University, notes, “Broad survey missions such as Kepler have revealed the variety of planets that exist in our galaxy. GPI will allow us to study a few dozen planets in exquisite detail.”
Contact: Bruce Macintosh (925) 423-8129 (macintosh1@llnl.gov).
A team of Livermore researchers has combined ultrafast time-resolved experiments with molecular dynamics simulations and thermochemical calculations to reveal how an explosive responds to a high-pressure shock from the moment of impact to the time of detonation. The results, which are featured on the cover of the December 12, 2013, issue of Journal of Physical Chemistry A, represent a milestone in understanding chemical initiation and detonation.
The team worked with hydrogen peroxide, which is composed of one oxygen–oxygen bond and two oxygen–hydrogen bonds within a hydrogen-bonding network. Sorin Bastea, who led the research team, says, “Hydrogen peroxide is a relatively simple molecular liquid that gives us the opportunity to study a very complex process.” Livermore physical chemist Nir Goldman, who along with Will Kuo led the project’s simulation efforts, adds, “What is unique about this research is that we have experimental data that corroborate our theoretical predictions on the exact same timescale.”
In shock-wave experiments led by Mike Armstrong and Joe Zaug, a 0.001-millimeter-thick aluminum film in contact with the peroxide was hit with a very short burst of laser energy. Using optical interferometry, the researchers then measured the speed of the shock wave as it traveled through the fluid. The peroxide began to tear apart 50 picoseconds (50-trillionths of a second) after the sample was shocked, and by 100 picoseconds, chemical bonds were completely broken. The temperature increased by more than 1,500 degrees, and the explosive pressure wave spiked to more than 200,000 atmospheres (20 gigapascals). Thermochemical calculations showed that the amount of chemical reaction in the experiments was approximately 50 percent.
Contact: Sorin Bastea (925) 422-2178 (bastea2@llnl.gov).