The resulting quarks stick around for a fleeting moment, and then they instantaneously recombine. This instability makes quarks extremely difficult to study, requiring complex equipment such as giant accelerator machines, which create the tiny subatomic collisions.

Now, researchers at the University of Calgary, Alberta, and the Argonne National Laboratory in Illinois, predict there may be another way to study quarks: By examining a special type of super-dense star called a neutron star.

Neutron stars are so dense that a teaspoon full of their material would weigh billions of tons. This density creates intense pressure at the core of the star - so much pressure that in some cases quarks could be squeezed out of their usually tight groupings and become free.

The freeing process, called quark de-confinement, effectively would turn a normal neutron star into what the researchers call a quark star. During the birthing process, massive amounts of energy would be released, producing a quark-nova - a theoretical implosion that, if real, could help scientists understand certain massive energy bursts in the universe that can be observed but not explained.

"Quark stars are the only place we would expect to see quarks ranging free in nature," said lead researcher Rachid Ouyed, of the University of Calgary. "So the universe has provided us with a natural laboratory to study their properties."

Reporting at the 208th meeting of the American Astronomical Society, co-author Prashanth Jaikumar, of Argonne, said the team has conducted theoretical studies of quark stars � an important process, because quarks are the building blocks of all matter, and knowing how they behave helps scientists understand fundamental principles of physics more deeply.

"If quarks exist in a stable form inside a star, they probably will change the properties of that star," Jaikumar said.

The researchers began by calculating the optimum conditions for forming quark stars. They found that the best candidates are fast-spinning neutron stars with masses between 1.5 and 1.8 times the Sun's. That means about one out of every hundred known neutron stars could be a quark star.

"If our theory turns out to be correct, then we could see two quark-novae every day," Ouyed said, noting that quark stars could be fairly common in the Milky Way.

"Our calculations also suggest that the core of highly magnetized heavy neutron stars can turn into quark matter within a few hours following their birth," said Jan Staff of the University of Calgary. He said heavy neutron stars with average magnetic fields could take up to 1,000 years to free quarks in their core - an extremely quick time period on the cosmic scale, however.

The next research step is to figure out what special properties quark stars and quark-novae might exhibit that scientists could observe. So far, there are a couple of possibilities.

First, the researchers think quark stars probably produce similar emissions as neutron stars - except for certain radio emissions. This lack of radio-emissions already has been observed in a stellar class known as radio-quiet neutron stars, comprising about seven known bodies. If the quark star theory is correct, those seven quiet stars could be quark stars.

The quark-star theory also could explain the existence of another puzzling astrophysical phenomenon known as gamma-ray bursts - stellar objects that occasionally emit about a million times more energy in a few seconds as the Sun emits in a year.

"For 40 years nobody has been able to explain this phenomenon," Ouyed said. "For a long time, we thought that a supernova was the most energetic thing in the universe. Now, we know that gamma-ray bursts are 10 times more powerful, but we've never been able to explain why."

Ouyed said he and another group of University of Calgary colleagues think that gamma ray bursts might be associated with quark-novae. In computer simulations, they have predicted how a neutron star's magnetic field changes as it evolved into a quark star.

The team's simulations show an explosion that releases energy comparable to gamma-ray bursts, so they now plan to use their simulations to predict other properties of quark stars and their birth.

"If we can actually find a quark-nova," Ouyed said, "it would be the most explosive phenomenon in the universe."

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