Researchers smashing gold atoms together to mimic conditions in the first microseconds after the creation of the universe have observed an unexpected new state of matter.

Instead of the thin fiery gas of quarks and gluons that they expected, they found instead a dense drop of the elementary particles that behave like a hitherto-unseen “perfect fluid.”

It is “a truly stunning finding,” said Raymond Orbach, director of the Department of Energy’s Office of Science.

Quarks are the fundamental building blocks of protons, neutrons and other sub-atomic particles, held together in pairs and triplets by mysterious particles called gluons, whose attractive force is so overwhelming that neither quarks nor gluons have ever been seen separated from one another in nature.

When the universe was created, however, it consisted only of a massive swarm of gluons and quarks, a so-called quark-gluon plasma, which quickly condensed into conventional matter.

Four separate international teams now believe that they have created a very small, short-lived quark-gluon plasma whose behavior will provide new insights into the moments after the Big Bang.

“We think we are looking at a phenomenon (very similar to what happened) in the universe 13 billion years ago when free quarks and gluons … cooled down to the particles that we know today,” said Sam Aronson of the Brookhaven National Laboratory, where the experiments were performed.

Aronson spoke Monday at a news conference at a meeting of the American Physical Society in Florida, where the results were presented.

“The matter that they are seeing is even more interesting … than we thought it would be,” said theoretical physicist Berndt Mueller of Duke University. “They have presented a compelling case for the achievement of an important milestone in the quest for the quark-gluon plasma,” a quest that has been under way since the development of modern nuclear physics.

The finding was so unexpected that the teams spent more than two years confirming their results. Their conclusion will be published soon in four papers in the journal Nuclear Physics A.

During the 1990s, researchers experimented by smashing hydrogen atoms and other small particles together at speeds approaching that of light — so-called relativistic velocities. But those collisions were too small to produce the energies necessary to form a quark-gluon plasma.

In 1999, Brookhaven finished construction of the Relativistic Heavy Ion Collider, which allowed collisions between atoms as large as gold at the highest energies ever achieved in manmade particle accelerators. Experimental runs began the next summer, and researchers have now compiled data from hundreds of millions of collisions, each producing thousands of particles.

Because the collisions produce temperatures 150,000 times that of the core of the sun, theoretical physicists such as Mueller predicted that the quark-gluon plasma would be a gas in which individual components would streak in every direction in an uncoordinated fashion.

What the teams found, instead, was that the particles in the plasma formed a liquid in which the individual components moved in a coordinated fashion, much like a school of fish in the ocean. “The data indicate that it is the most perfect fluid we have ever seen,” Mueller said.

A perfect fluid is a theoretical ideal, a low-viscosity, frictionless liquid whose behavior is described precisely by the equations of fluid mechanics.