NASA research simulates how cold stars stay in shape


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In research with the potential to help study stars and improve space navigation, scientists have successfully used lasers to cool a cloud of lithium atoms sufficiently to observe unusual quantum properties of matter. Although current technology does not permit humans to travel to the stars, scientists can create a simulated star laboratory on Earth.

The scientists, at Rice University in Houston, TX, successfully simulated and photographed the process by which white dwarfs and neutron stars retain their size and shape, a mechanism called Fermi pressure. White dwarfs and neutron stars are dense, compact objects created when normal stars use up their fuel, cooling and succumbing to the forces of gravity.

"This not only increases our understanding of the basic laws of nature, but also lays the foundation for the development of far-reaching technologies for deep space navigation," said Dr. Kathie Olsen, Acting Associate Administrator for Biological and Physical Research (BPR) at NASA Headquarters, Washington, DC.

Fermi pressure, named for Dr. Enrico Fermi, a Nobel Laureate prominent for his contributions in nuclear physics, has been theorized as the star stabilization mechanism, which keeps white dwarfs and neutron stars from collapsing further. NASA's Hubble Space Telescope and Chandra X-ray Observatory have observed such objects but this is the first time Fermi pressure has been directly observed in an Earth laboratory. The research by the Rice team, led by Dr. Randall Hulet, was conducted under a grant from NASA's Biological and Physical Research Program through NASA's Jet Propulsion Laboratory, Pasadena, CA.

"Many quantum effects have been theorized in the past 70 years, but only in the most recent years have scientists been able to create laboratory environments sophisticated enough to systematically test them," said Dr. Mark Lee, BPR fundamental physics discipline scientist. "We are really elated and proud that this newly established NASA program has yielded results of such high significance."

The successful observation of Fermi pressure in the laboratory is the first step toward other advances, including improvements in atomic clocks, the most accurate of timekeepers. New clocks could be designed using these ultra- cold atoms so that the atoms collide less frequently, which would lead to even greater accuracy. More precise clocks would help digital communications systems and improve deep space navigation.

"Experimenting with Fermi pressure may also lead to the creation of a new type of superfluid from lithium," said Hulet, physics professor at Rice University. Superfluids, in which atoms flow without friction, are quantum systems very similar to superconductors, which have zero resistance to electrical current flow. This new super-cold system of atoms could provide scientists a new testbed for theories of superconductivity and show promise in solving some of the world's energy problems.

Hulet's team cooled lithium to less than one-fourth of a millionth of a degree above absolute zero. Absolute zero is the point at which scientists believe there can be no further cooling. At these ultra-low temperatures, the researchers were able to view and photograph two stable lithium isotopes, identical except for the number of neutrons they contain. They were thus able to demonstrate the star-stabilizing pressure. However, on Earth this type of research is hampered by gravity. The microgravity environment on the International Space Station, when it is completed, will eventually serve as an ideal location to study the transition to a superfluid.

Hulet co-authored the quantum experiment paper, which appears in the March 30 issue of the journal Science, with Rice University post-doctoral scientist Dr. Andrew Truscott, graduate students Kevin Strecker and Guthrie Partridge, and Dr. William McAlexander, now with Agilent Laboratories, Palo Alto, CA.