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Fierce Flash, Strange Star

Two mysteriously bright gamma ray flashes may have been caused by the strangest stars in the universe, according to a paper in the 9 July edition of Physical Review Letters. The study provides the best evidence yet that in some stars, quarks are free to roam, rather than being bound inside nuclear particles.

On 5 March 1979, what looked like an ordinary neutron star in the nearby Large Magellanic Cloud spewed an enormous amount of energy. The blast, as well as one from another star the following year, ought to have torn the stars into shreds, says Vladimir Usov, a physicist at the Weizmann Institute of Science in Rehovot, Israel. But both stars are still there, and astronomers have been at a loss to explain why they survived.

To solve the mystery, astronomer Charles Alcock of the University of Pennsylvania in Philadelphia postulated more than a decade ago that the flaring stars were not ordinary neutron stars; Instead, they were hypothetical "strange stars," which are so tightly squeezed that the individual neutrons break apart into their components, called quarks. When a comet-sized lump of matter strikes a quark star, the infalling material also gets "quarkonized," or split into its component quarks, releasing a great deal of energy. Because a strange star is held together by stronger forces than a neutron star is, it wouldn't tear itself apart.

Usov extended Alcock's idea by making a detailed calculation of the amount of light that would come off of such a collision. "The luminosity is not only great--it's huge," says Usov. Furthermore, Usov calculated the peak brightness, the duration, and several other properties of the flare, which each match the observations of the gamma ray bursts.

Although Usov's model fails to account for all properties of the flares, "I think he's doing quite an interesting thing here," Alcock says. He believes the work will help theorists figure out the nature of strange stars, if they actually exist. "He really has advanced our understanding of how [strange stars] behave."

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