U.S. researchers have captured a movie of a single electron moving through a container of extremely cold liquid helium, a feat once thought impossible.

Humphrey Maris, a professor of physics at Brown University in Providence, R.I., and doctoral candidate Wei Guo used pulses of high-intensity sound to capture an image of the subatomic particle.

The electron, which weighs one octillionth of a gram — a decimal point followed by 26 zeroes and a one — is seen in the video as points of light.

"We were astonished when we first saw an electron moving across the screen," Maris said in a written statement.

The feat was made possible by using sound to expand bubbles that form around the electron as it moves through the liquid helium and flashing a strobe light to capture the image on video.

As the electron moves through the helium, it repels atoms around it, creating the space or bubble. Because the bubbles are too tiny to see, researchers used sound pulses to expand them to about eight microns in size — about the scale of a speck of dust.

The video was first shown at the International Symposium on Quantum Fluids and Solids in Kyoto, Japan, in 2006, and images from the video were published online in the Journal of Low Temperature Physics at the end of May.