Ultraviolet light excites hydrogen atoms in the gas clouds, causing them to emit a characteristic wavelength of red light called the Lyman alpha wavelength, which Rauch compared to "a flagpole that sticks out from the spectrum."
The research involved repeatedly aiming the 26-foot (8-meter) Very Large Telescope in Chile at the same tiny patch of sky for the equivalent of nearly two weeks' worth of night observing—about 92 total hours of observation.
But instead of gas clouds, the researchers ended up detecting 27 faint galaxies, all shining at the same wavelength because of ultraviolet light emitted during the process of star formation.
"Whenever the conditions were right, the on-site astronomers in Chile would take data for us, over a three-year period," Rauch said. "It's probably the deepest [longest-duration] spectra in the history of astronomy."
The research will be published in the March issue of the Astrophysical Journal.
Boots on the Ground
According to the Carnegie Institution, the new objects are ten times fainter than any galaxies before seen from the ground.
That's a triumph for ground-based astronomy, which has been surpassed in many people's eyes by orbiting observatories such as NASA's Hubble Space Telescope.
Hubble and its kin can't make extended spectroscopic observations of the same small area. (Read more on the debate between ground- and space-based telescopes).
The next generation of terrestrial telescopes are expected to keep pace with the newest orbiting telescopes, raising hopes for further discoveries.
"They're highly complementary approaches," Rauch said.
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