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. More information on the experiment and the BPR
Fundamental Physics Program can be found at:
http://funphysics.jpl.nasa.gov
Hulet’s research was funded by NASA, the Office of Naval
Research, the National Science Foundation, and the R.A. Welch
Foundation. NASA’s Jet Propulsion Laboratory manages the
Fundamental Physics in Microgravity Research Program for
NASA’s Office of Biological and Physical Research,
Washington, DC. JPL is a division of the California Institute
of Technology in Pasadena.
