|This image from a simulation of galaxy formation shows streams of gas feeding the growing galaxy.
To compile the list, an editorial team at Physics World reviewed more than 350 news articles about breakthroughs in the physical sciences published on their web site in 2011. The criteria for judging included "fundamental importance of research; significant advance in knowledge; strong connection between theory and experiment; and general interest to all physicists."
The original article appeared online in Science on Nov. 10. Prochaska, a professor of astronomy and astrophysics, and Fumagalli, a UC Santa Cruz graduate student, analyzed light from distant quasars to detect two pristine clouds of the primordial gas that formed in the first few minutes after the Big Bang. Their observations matched theoretical predictions, providing direct evidence in support of the modern cosmological explanation for the origins of elements in the universe.
"As hard as we've tried to find pristine material in the universe, we have failed until now. This is the first time we've observed pristine gas uncontaminated by heavier elements from stars," Prochaska said.
"The lack of metals tells us this gas is pristine," Fumagalli said. "It's quite exciting, because it's the first evidence that fully matches the composition of the primordial gas predicted by the Big Bang theory."
The researchers discovered the two clouds of pristine gas by analyzing the light from distant quasars, using the HIRES spectrometer on the Keck I Telescope at the W. M. Keck Observatory in Hawaii. By spreading out the bright light from a quasar into a spectrum of different wavelengths, the researchers can see which wavelengths were absorbed by material in between the quasar and the telescope.
"We can see absorption lines in the spectrum where the light was absorbed by the gas, and that allows us to measure the composition of the gas," Fumagalli said.
For more on their discovery, see "Astronomers find clouds of primordial gas from the early universe."