PHYSICISTS have been struggling for years to create an ultra-dense material called quark matter by smashing particles together at high energies. But there might be an easier way to find the stuff. It seems that massive balls of quark matter exist in space.
Astronomers using the orbiting Chandra X-ray Observatory stumbled across the discovery while looking at the debris from recent supernovae, the titanic explosions that happen when stars run out of fuel. In a supernova, a star鈥檚 core is thought to collapse so rapidly that atomic nuclei are squashed into a soup of neutrons. The process compresses material weighing as much as our Sun into a neutron star the size of a large city.
But Jeremy Drake and his team at the Harvard-Smithsonian Center for Astrophysics in Cambridge, Massachusetts, have found that the nearby star RX J1856 is about 11 kilometres across, a little too small even to be a neutron star.
Advertisement
The star鈥檚 small size only makes sense if the 1983 supernova that became RX J1856 smashed the neutrons together so violently that they dissolved into their constituent quarks, creating a superdense quark star. 鈥淭his is an astonishing discovery with fundamental significance,鈥� says Norman Glendenning, a neutron star theorist at the Lawrence Berkeley National Laboratory.
The star鈥檚 X-ray spectrum shows it to be at a temperature of 700,000 掳C, 100 times that of our Sun. Yet when Drake鈥檚 team looked at the star with the Hubble Space Telescope, they saw that it was giving out hardly any visible light. 鈥淚t鈥檚 an extremely faint blue star,鈥� says Drake. Something so hot can only be so faint in visible light if it is very, very small, he says.
Not everyone is convinced, however. Mike Turner, an astrophysicist at the University of Chicago says the team might merely have spotted a hot spot on the surface of a larger neutron star. 鈥淰ery few people will be convinced that this is an ironclad case,鈥� he says.
But Turner is encouraged by a similar discovery made by David Helfand and his team at Columbia University in New York City. They say the surviving core of a star that went supernova around 1180 AD has cooled down more than theorists would expect for a young neutron star. This suggests it contains exotic matter in which various kinds of quark roam free, making them freer to generate other particles that carry heat away.
If confirmed, the discoveries are good news for particle physicists. Quarks are the most fundamental constituents of matter, but they are hard to study because they are usually trapped inside the neutrons and protons of atoms.
But quark stars might make it easier to study quarks. For example, researchers could pin down the mass of the 鈥渟trange鈥� quark by taking a census of quark stars. If strange quarks are very heavy, quark stars will be less likely to form. 鈥淣ature has carried out an experiment we cannot duplicate on Earth,鈥� says Turner.