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Cosmic blasts could signal strange state of matter 

June 5, 2006
Courtesy University of Calgary
and World Science staff

Quarks, matter’s smallest known building blocks, don’t reveal themselves easily. Scientists can study them only by bashing subatomic particles together so that they break into their constituent quarks. But these stick back together again an instant later, and the show is over.

Quark stars contain quarks liberated from the confines of neutrons, subatomic particles that contain triplets of quarks. Quark stars are also called strange stars because they contain a type of quark called "strange" quarks. (Courtesy Chandra X-ray Observatory)

Now, researchers suggest there is another way to study quarks, by examining certain super-dense stars called neutron stars. These are so compact that a teaspoon full of their material would weigh billions of tons. 

The density creates such high pressure at the core that quarks sometimes could be squeezed out of their usually tight groupings, and become free. This liberation, called quark deconfinement, would turn a normal neutron star into a “quark star.” 

Astronomers have already found a few objects that they theorize may be quark stars.

But Rachid Ouyed, an astrophysicist at the University of Calgary in Canada, and a group of colleagues also propose that their formation could release massive amounts of energy, producing a type of implosion they call a “quark nova.” That, they add, may help explain certain hitherto mysterious cosmic blasts.

“Quark stars are the only place we would expect to see quarks ranging free in nature,” said Ouyed. His group plans to present findings of their theoretical studies June 5 at the American Astronomical Society meeting in Calgary.

Most likely to become quark stars are fast-spinning neutron stars with masses between 1.5 and 1.8 times that of our sun, they calculated. Thus one in every hundred known neutron stars could actually be a quark star. 

“If our theory turns out to be correct, then we could see two quark-novae every day,” said Ouyed, adding that quark stars may be fairly common.

Quark stars probably look like normal neutron stars except they don’t emit certain radio waves, the researchers argue.  This peculiarity has already been noted in a class of neutron stars described as “radio-quiet,” about seven of which are known. Thus, these may be quark stars, the scientists say.

The theory may also explain another puzzling phenomenon known as gamma- ray bursts, the group claims—explosions that occasionally let out, in a few seconds, about a million times as much energy as our sun does in a year. 

Ouyed argues that these may be linked to quark-novae. In computer simulations, he and colleagues have predicted how a neutron star’s magnetic field would change as it becomes a quark star. The simulations, also to be presented at the meeting, show an explosion with energy comparable to that of gamma- ray bursts.

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