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:
http://funphysics.jpl.nasa.gov
