By spinning ultra-cold sodium gas in a laboratory, NASA-funded scientists at the Massachusetts Institute of Technology (MIT) in Cambridge have created a gas cloud that resembles rounded Swiss cheese and is riddled with tiny whirlpools, like those that cause "starquakes" in space.
This research may teach scientists more about the history of our universe and the stars within it and may eventually lead to vast improvements in highly precise atomic clocks.
The laboratory demonstration is related to puzzling glitches observed by astronomers in the otherwise smooth, rapid rotation of pulsars. A pulsar is a type of neutron star, a remnant of a dying star and one of the densest objects in the universe. Glitches in pulsar rotation are called "starquakes" and may occur when whirlpools, or vortices, form or decay.
"This was a breathtaking experience when we saw these vortices," said Dr. Wolfgang Ketterle, an MIT physics professor who led the research team. "We took this ultra-cold, fragile gas, and we were amazed that even though we put hundreds of whirlpools into it, the gas cloud remained stable and happy."
Ketterle and his colleagues, who conducted the research under a grant from the Biological and Physical Research Program through NASA's Jet Propulsion Laboratory, Pasadena, Calif., cooled the sodium gas to less than one millionth of a degree above absolute zero (-273 Celsius or -460 Fahrenheit). At such extreme cold, the gas cloud converts to a peculiar form of matter called Bose-Einstein condensate, as predicted 75 years ago by Albert Einstein.
No physical container can hold such ultra-cold matter, so Ketterle's team used magnets to keep the cloud in place. They then used a laser beam to make the gas cloud spin, a process Ketterle compares to "stroking a ping-pong ball with a feather until it starts spinning."
The spinning sodium gas cloud, whose volume was one- millionth of a cubic centimeter, much smaller than a raindrop, developed a regular pattern of more than 100 whirlpools.
Previously, scientists in a laboratory had seen only one or a few quantum whirlpools in a superfluid; this was the first direct observation of many whirlpools. Both the sodium gas cloud and pulsars are superfluids, which allow matter to flow without friction. Scientists know that superfluids form quantum whirlpools as they rotate; quantum whirlpools reflect the smallest possible increase in rotation for the cloud or the pulsar. One might expect different behavior from the two systems, because the gas cloud is 100,000 times thinner than air, while a pulsar is about ten thousand trillion times denser than air.
"This was an example of a designer quantum system, where we make something happen in the laboratory that doesn't occur naturally on Earth," said Dr. Mark Lee, fundamental physics discipline scientist for the Office of Biological and Physical Research at NASA Headquarters, Washington, D.C. "Astronomers had observed these phenomena on pulsars but had no opportunity to manipulate them, until now."
The scientists were also challenged with how to photograph the quantum whirlpools, which were too small to be seen except with special magnification. They switched off the magnets containing the gas cloud, allowing it to expand to 20 times its original size, which made the whirlpools large enough to be photographed. As the cloud expanded, gravity made it fall, and the team had to take the picture quickly. These gravitational limitations would be absent in the near- weightless environment that will soon be available to researchers on the International Space Station.
Ketterle co-authored the quantum experiment paper, which is currently scheduled to appear in the April 20 issue of the journal Science, with Jamil Abo-Shaeer and Drs. Chandra Raman and Johnny Vogels, all of MIT. The research was funded by NASA, the National Science Foundation, the Office of Naval Research, the Army Research Office and the David and Lucile Packard Foundation. JPL manages the Fundamental Physics in Microgravity Research Program for NASA's Office of Biological and Physical Research. JPL is a division of the California Institute of Technology in Pasadena.
Visual depictions of the experiment are available at http://www.jpl.nasa.gov/pictures/funphysics .
More information on the experiment and NASA's Biological and Physical Research Fundamental Physics Program can be found at the following web sites:
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