A NEW kind of star may be lurking in the debris from a nearby supernova explosion. If confirmed, the 鈥渜uark star鈥� could offer fresh insights into the earliest moments of the universe.
When supernovae explode, they leave behind either a black hole or a dense remnant called a neutron star. However, recent calculations suggest a third possibility: a quark star, which forms when the pressure falls just short of creating a black hole.
Astronomers believe these form after the neutron star stage, when the pressure inside a supernova rises so high the neutrons disintegrate into their constituents 鈥� quarks. These form an even denser star than neutrons.
Advertisement
Observing a quark star could shed light on what happened just after the big bang, because at this time, the universe was filled with a dense sea of quark matter superheated to a trillion 掳C. While some groups have claimed to have found candidate quark stars, no discovery has yet been confirmed.
Now Kwong-Sang Cheng of the University of Hong Kong, China, and colleagues have presented evidence that a quark star formed in a bright supernova called SN 1987A (pictured), which is among the nearest supernovae to have been observed.
The birth of a neutron star is known to be accompanied by a single burst of neutrinos. But when the team examined data from two neutrino detectors 鈥� Kamiokande II in Japan and Irvine-Michigan-Brookhaven in the US 鈥� they found that SN 1987A gave off two separate bursts. 鈥淭here is a significant time delay between [the bursts recorded by] these two detectors,鈥� says Cheng. They believe the first burst was released when a neutron star formed, while the second was triggered seconds later by its collapse into a quark star. The results will appear in The Astrophysical Journal ().
鈥淭his model is intriguing and reasonable,鈥� says Yong-Feng Huang of Nanjing University, China. 鈥淚t can explain many key features of SN 1987A.鈥� However, Edward Witten of the Institute for Advanced Study in Princeton, New Jersey, is not convinced. 鈥淚 hope they鈥檙e right,鈥� he says. 鈥淢y first reaction, though, is that this is a bit of a long shot.鈥�
High-resolution X-ray observatories, due to fly in space in the next decade, may have the final say. Neutron stars and quark stars should look very different at X-ray wavelengths, says Cheng.
