Quark stars may hold keys to quantum mysteries
UNIVERSITY OF CALGARY NEWS RELEASE
Posted: June 8, 2006
Quarks, the smallest building blocks of all matter, are mysterious and elusive -- so elusive, in fact, that scientists can only study them by smashing subatomic particles against one another at super-high speeds so they break into their constituent parts. 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 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 deconfinement, would effectively turn a normal neutron star into a "quark star." During this birthing process, massive amounts of energy would be released, producing what researchers at the University of Calgary and Argonne National Laboratory in Illinois have dubbed a "Quark-Nova" -- a theoretical implosion that, if it exists, may 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," says professor Rachid Ouyed, a University of Calgary astrophysicist and lead researcher of the project. "So the universe has provided us with a natural laboratory to study their properties."
Ouyed has conducted theoretical studies of quark stars along with doctoral candidate Jan Staff of the University of Calgary and Prashanth Jaikumar, a postdoctoral associate with the Argonne National Laboratory, which is managed by the University of Chicago. Staff presented the group's findings this week at the American Astronomical Society meeting in Calgary.
Studying the properties of quarks is important because they are building blocks of all matter, and knowing how quarks behave helps scientists better understand fundamental principles of physics. Jaikumar, who studies the theory of quarks, teamed up with Ouyed and Staff so they could begin to make new predictions about the properties of the free-ranging quarks found in quark stars. "If quarks exist in a stable form inside a star, they probably will change the properties of that star," he says.
So if quark stars really do exist, how can scientists find them? The researchers set out to answer that question by calculating the optimum conditions for forming quark stars. The best candidates? Fast-spinning neutron stars with masses between 1.5 and 1.8 times the mass of our sun. That means about one out of every hundred known neutron stars could in fact be a quark star.
"If our theory turns out to be correct, then we could see two Quark-Novae every day," says Ouyed, noting that quark stars may actually be fairly common in our galaxy.
"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," says Staff. He says that heavy neutron stars with average magnetic fields may take up to 1,000 years to free quarks in their core -- an extremely quick time period on the cosmological scale.
The next step in the research is to figure out what special properties quark stars and Quark-Novae exhibit that scientists could observe. So far, the researchers have at least a couple of ideas. First, they think quark stars probably produce similar emissions as neutron stars -- except for certain radio emissions. This lack of radio-emissions has already been observed in a class of neutron stars known as radio-quiet neutron stars, about seven of which are known. If the quark star theory is correct, it's possible those seven quiet stars are in fact quark stars.
The quark star theory may also explain the existence of another puzzling astrophysical phenomenon known as gamma ray bursts -- stellar objects that occasionally emit about a million times as much energy as our sun does in an entire year, only in a few seconds.
"For 40 years nobody has been able to explain this phenomenon," Ouyed says. "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 and another group of University of Calgary colleagues (including master's student Brian Niebergal, astrophysicist Denis Leahy and research associate Wolfgang Dobler) think that gamma ray bursts may be associated with Quark-Nova. In computer simulations, they've already predicted how a neutron star's magnetic field would change as it became a quark star. The simulations -- which are also being presented at the American Astronomical Society meeting -- show an explosion that releases energy comparable to that of gamma ray bursts. The researchers plan to use their simulations to predict other properties of quark stars and their birth.
"If we can actually find a Quark-Nova," says Ouyed, "it would be the most explosive phenomenon in the universe."