Was the brightest supernova the birth of a quark star?
By David Shiga The breakdown of matter into its tiniest quark components in a star’s core may have triggered the brightest supernova ever seen, a controversial new study says. If correct, this would be the first time anyone has seen the birth of an exotic object called a quark star. On 18 September 2006, astronomers observed the record-breaking supernova, called 2006gy, and were shocked to find that it was intrinsically about 100 times brighter than typical stellar explosions. To explain its extreme power, its discoverers invoked an unusual argument based on the creation of pairings of matter and antimatter particles inside a massive star (see Did antimatter factory spark brightest supernova?). Now, Denis Leahy and Rachid Ouyed, both of the University of Calgary in Alberta, Canada, have proposed an even more exotic scenario – the fantastically violent birth of an object called a quark star. Quarks are subatomic particles that normally only associate in groups of two – producing short-lived mesons, or three – producing the protons and neutrons that make up the bulk of normal matter. But some physicists say that when matter is crushed to extreme densities, it settles into a soup of individual quarks. A cubic centimetre of this new type of matter – dubbed ‘strange’ after one of the six types of quark – would weigh as much as a billion tonnes and would have the unusual property of converting any ordinary matter that touches it into more strange matter, releasing energy in the process. The energy released by converting the core of a star into strange matter would cause an explosion called a quark nova, which Leahy and Ouyed argue has been observed for the first time in SN 2006gy. In their picture, the event begins when a massive star blasts away its outer layers in an ordinary supernova explosion. In the process, the star’s core collapses to become a dense object called a neutron star. But the team argues that some neutron stars last only a short time because their magnetic properties cause their spin rates to drastically slow down. Because centrifugal force can no longer support the neutron star’s core, it collapses even further, transforming into strange matter. The transformation releases a tremendous amount of energy, blasting the neutron star’s outer layers into space at close to light speed. The layers then slam into debris from the original supernova, creating an intense glow bright enough to explain the observations of SN 2006gy, Ouyed told New Scientist. Showing that quark stars exist would be of great interest to physicists, who have not been able to solve the equations describing how matter behaves at extremely high densities to determine whether strange matter is stable. “Strange matter may exist or it may not,” says Fridolin Weber of San Diego State University in California, US. “It’s not proven theoretically – it’s an open issue.” Stanford Woosley of the University of California in Santa Cruz, US, agrees. “The physics of quark novae is at best uncertain,” he told New Scientist, adding that the quark nova explanation for this object is “a really exotic model that is quite unnecessary”. Ouyed says further evidence for the quark nova scenario could come from continued monitoring of the aftermath of SN 2006gy, which could show signs of rare elements with an atomic weight greater than 130. These could only be produced in the quark nova scenario, he says. Still, he does not rule out other scenarios. “If they can do a better job, then we’re willing to listen,