Research Highlights

What do fermions in atomic nuclei, neutron stars, and ultracold trapped gases have in common? They have the same fundamental behavior. The exciting news is that there's now hard evidence that this is true, thanks to graduate students Jayson Stewart and John Gaebler, Cindy Regal who received her Ph.D. in physics in November, and Fellow Debbie Jin.

When illuminated by X-ray and infrared light beams in tandem, electrons can tap dance off a platinum surface because they've actually grabbed a photon from both beams simultaneously. As you might have guessed, there is more going on here than the ordinary photoelectric effect, which Albert Einstein explained more than a century ago. In the photoelectric effect, electrons escape from a solid after absorbing a single photon or bundle of light energy. 

For astrophysicists working to discover the origins of stars and planets, a small clue can go a long way. They can't get a close look at distant stars and planets, so they only know the barest details about other planetary systems. One such detail is that some extra-solar planets revolve around their stars in elliptical orbits rather than the nearly circular orbits that are the norm in our solar system. 

Left to their own devices, deuterium atoms would attach themselves to cold specks of soot floating in interstellar gas clouds and remain there for eternity. In fact, deuterium has a great affinity for the buckyballs, bucky onions, bucky tubes, and other forms of carbon, such as polycyclic aromatic hydrocarbons, comprising soot. It readily replaces hydrogen in these molecules. Deuterium atoms bond to interstellar soot so tightly it takes an encounter with a hot star or supernova explosion to pry them loose.

"Chemistry is a highly improbable science," says Graduate Student Mike Deskevich, who adds "It's good for life on Earth that things are so unreactive." For instance, if chemical reactions happened easily and often, oxygen in the air would cause clothing and other flammable materials to burst into flame. In addition to making life difficult, high probability chemistry would render theoretical chemical physics much less interesting. As it is, theorists spend months determining the particular molecular shapes, vibrations, and energy states that make the simplest chemical reactions possible.

When will the Laser Interferometer Space Antenna (LISA) fly? Fellows Jim Faller and Peter Bender first proposed the basic concept behind LISA more than 25 years ago. The joint European Space Agency/NASA mission first scheduled a possible launch in 2012. The date has now slipped to 2017, with additional delays possible. Both agencies are grappling with limited budgets and conflicting priorities. In the United States, plans for a future manned spaceflight to Mars are competing for funding with basic science-oriented space programs like LISA.

The breakdown of chlorofluorocarbons (CFCs) in the stratosphere has been implicated in the destruction of Earth's protective ozone layer. Consequently, scientists have undertaken studies to better understand the structure and behavior of highly reactive, but short-lived, free radicals produced during the breakdown process. The molecules, which contain either fluorine or chlorine, are an important source of atmospheric halogen atoms. Elucidating their 3D structure and dynamical behavior will help scientists better understand atmospheric chemistry as well as their fundamental molecular properties.

A solvent is something that dissolves or disperses something else. It's the water in salt water, the alcohol in cough syrup, the lactates or ethers in inks. For many of us, solvents are the background music of the chemistry taking place all around us. But this isn't how Fellow Carl Lineberger and his colleagues in chemical physics think about solvents. Lineberger, Former Research Associate Vladimir Dribinski, Graduate Students Jack Barbera and Josh Martin, and student visitor Annette Svendsen see them as key players in some chemical reactions, right down to the level of quantum mechanical interactions.

"In the right light, in the right time, everything is extraordinary," according to photographer Aaron Rose. He could have just as easily been describing precision optical spectroscopy experiments recently conducted by Research Associates Tanya Zelevinsky and Tetsuya Ido, Graduate Students Martin Boyd and Andrew Ludlow, Fellow Jun Ye and collaborators from Poland's Instytut Fizyki and NIST's Atomic Physics Division.

Life can be challenging on the biophysics research frontier. Consider gold nanoparticles as a research tool, for example. Gold is ductile and malleable as well as being a good conductor of heat and electricity. Its unique chemistry allows proteins and DNA to be easily attached to these nanoparticles. Physicists have been investigating gold nanoparticles in optical-trapping experiments because they enhance trapping efficiency and potentially increase detection sensitivity.

The fine structure constant is getting a lot of attention these days. Known as α, it is the "coupling constant," or measure of the strength of the electromagnetic force that governs how electrons, muons, and light interact. What's intriguing is that new models for the basic structure of matter predict that α may have changed over vast spans of cosmic time, with the largest variations occurring in the early universe. However, the Standard Model says a has always been the same. Our basic understanding of physics depends on scientists' ability to determine whether or not α is an "inconstant constant."

There's only one way to prove you've invented a better atomic clock: Come out on top of a comparison of your clock with one of the world's best atomic clocks: The NIST-F1 cesium fountain atomic clock, the nation's primary time and frequency standard. NIST-F1 is so accurate it won't gain or lose a second in more than 60 million years.

Galaxy clusters contain enormous clouds of gas whose cooling should result in the formation of a multitude of new stars. But that's not what NASA's Chandra X-ray Observatory is detecting. Instead there's a whole lot less gas cooling and new star formation than scientists had predicted. Perhaps the most mysterious discovery of all is that the clusters are humming – a low B-flat 57 octaves below middle C. The hum originates from ripples of sound waves washing through great galactic gas clouds surrounding supermassive black holes.

Imagine trying to describe the intricate motions of a single atom as it interacts with a laser. Then suppose you could generalize this understanding to a whole cloud of similar atoms and predict the temperatures your experimental physicist colleagues could achieve with laser cooling. This way-cool theoretical analysis comes compliments of Graduate Student Josh Dunn and Fellow Chris Greene.

Juri Toomre and his group concentrate their stellar research close to home--just 93 million miles away, to be precise. They want to answer the question: What dynamic processes occur deep within the Sun? To find out, they use a powerful combination of computer simulations and helioseismology (which analyzes sound waves produced by the Sun to probe its internal structure.) The researchers believe that working out the details of the Sun's internal structure should lead to explanations for the 22-year sunspot cycle and other regular surface features such as the Sun's consistent, but variable, rotation rate.

Our lives depend on heme. As part of hemoglobin, it carries oxygen to our tissues. As part of cytochrome c, it helps transform the energy in food into the energy-rich molecule ATP (adenosine triphosphate) that powers biochemical reactions that keep us alive and moving. As part of cytochrome P450, it helps break down toxic chemicals in our bodies.

Science sleuths have a new and powerful method for identifying (and investigating) atoms and molecules, thanks to Graduate Student Mike Thorpe, Research Associate Kevin Moll, Senior Research Associate Jason Jones, Undergraduate Student Assistant Ben Safdi, and Fellow Jun Ye. The new method allows them to study molecular vibrations, rotations, and collisions as well as temperature changes and chemical reactions.

Gamma-ray bursts signal the birth of a new black hole, whether it's created during the collapse of a massive star or via a merger between two compact objects such as neutron stars. Astrophysicists have determined that long gamma-ray bursts are associated with collapsing stars and short bursts are associated with binary mergers. In both cases, however, black-hole accretion powers the burst. 

Black holes are pretty strange, sucking in not only nearby matter but also the space around it. These cosmic vacuum cleaners are powered by thin, gaseous accretion disks in orbit around them. Something drives the orbiting gas to spiral in toward the black hole, where all trace of it disappears forever into the singularity. One of the exciting challenges in astrophysics is to figure out the physics driving this process, which keeps black holes growing for billions of years after they're formed.

One fun thing theorists do is undertake creative projects that predict phenomena that haven't yet been observed experimentally. In fact, sometimes they even predict things no one has ever imagined before. In other cases, the goal is to unravel the mechanism behind an experimental result that initially seems to conflict with the known laws of quantum physics. Fellow Chris Greene's group enjoys self-driven, innovative work in both categories.