For the first time, astronomers have detected ancient and pristine clouds of primordial gas, conceived when the universe was a very young, dark and lonely place.

This long-sought discovery of 12-billion-year-old pockets of gas by UC Santa Cruz scientists offers a stunning snapshot of early cosmic history — and adds more support to the widely accepted big bang theory about the origin of elements in our universe.

“It’s thrilling. It describes all that we’ve been looking for,” said J. Xavier Prochaska, professor of astronomy and astrophysics, whose study is published in Thursday’s issue of the journal Science.

Staring into deep time within two patches of dark sky — one in the constellation Leo and the other Ursa Major — the team found clouds of hydrogen and a hydrogen isotope, called deuterium. Those two original elements, relics of the big bang — a mega-explosion that led to the expansion of the universe — are uncontaminated by more recent elements like carbon, nitrogen and oxygen.

The ancestral clouds are very, very faint, not visible to the naked eye. But powerful computers in a UC Santa Cruz basement can analyze their spectral images, captured by Hawaii’s Keck Telescope.

The discovery is significant because it props up the big bang theory of the origin of the elements. In the beginning, according to the hypothesis, hydrogen and helium were created during “the dark ages” of the universe — through nuclear reactions in the first few moments of creation.

But that could not be proven until now, because astronomers were able to detect only much newer elements, such as our beloved oxygen.

The primordial gas provided fuel for the very first stars — lighting up the darkness. These early stars were monsters that burned hot, lived fast and died young. Their deaths sent newer elements exploding into space, seeding galaxies with everything necessary for life.

More profoundly, the UCSC discovery is a reminder of the illuminating power of human reason, and how scientists can overcome seemingly insoluble problems using technology.

“We’ve been trying to find such pockets, because there was good reason to think they exist,” said Prochaska. “We’ve been aggressively looking for material that would match the theory.

“This is very pristine gas — exactly what the theory predicts,” he said. “It’s material not polluted by stars or galaxies.”

Turning the scientific process on its head, the discovery was made by the actual absence of data — what couldn’t be seen.

Light is absorbed by gas. So when light can’t be found, it reveals the composition of that gas.

All gases, and other elements, have unique “spectral” fingerprint. So the UCSC team did a spectrographic analysis of the fingerprints of the light. The light came from a super-bright quasar; fortunately, the clouds happened to be right in front of it.

The scientists’ computers spread out this light into a broad spectrum of different wavelengths — making it possible to identify which wavelengths were absorbed by the gas.

Looking for wavelengths of hydrogen, “we don’t see it. That light is removed,” meaning it is contained within the clouds, Prochaska said.

Ditto for deuterium. Scientists believe that the universe once had more deuterium than it does today — and the deuterium-to-hydrogen ratio in the gas clouds matches big bang predictions.

“It’s doing astronomy backwards,” explained Prochaska. “Most people look at stars, galaxies — things like color, shape, whatever. … But we don’t care about the light we receive. We care about light that we don’t receive. The dark spots.”

He added, “We’re doing science in silhouette — studying that light that doesn’t get here, due to the gas.

“We get excited about nothing,” he joked. “When it was immediately clear that nothing was there, that really floored us.”

Poignantly, these clouds likely no longer exist.

Powerful telescopes see distant objects as they were far back in time, not now. It takes a long time for light to travel across the universe.

“It’s very different today,” said Prochaska. “They’re probably not there at all.”

Contact Lisa M. Krieger at 408-920-5565.