or entirely of quark matter are called quark stars or strange stars. QCD matter may exist within the collapsar of a gamma-ray burst, where temperatures as high as 6.7 x 1013 K may be generated. At this time no star with properties expected of these objects has been observed, although some evidence has been provided for quark matter in the cores of large neutron stars. Strangelets. These are theoretically postulated (but as yet unobserved) lumps of strange matter comprising nearly equal amounts of up, down and strange quarks. Strangelets are supposed to be present in the galactic flux of high energy particles and should therefore theoretically be detectable in cosmic rays here on Earth, but no strangelet has been detected with certainty. Cosmic ray impacts. Cosmic rays comprise a lot of different particles, including highly accelerated atomic nuclei, particularly that of iron. Laboratory experiments suggests that the inevitable interaction with heavy noble gas nuclei in the upper atmosphere would lead to quark–gluon plasma formation. Quark matter with baryon number over about 300 may be more stable than nuclear matter. This form of baryonic matter could possibly form a continent of stability. Laboratory experiments Even though quark-gluon plasma can only occur under quite extreme conditions of temperature and/or pressure, it is being actively studied at particle colliders, such as the Large Hadron Collider LHC at CERN and the Relativistic Heavy Ion Collider RHIC at Brookhaven National Laboratory. In these collisions, the plasma only occurs for a very short time before it spontaneously disintegrates. The plasma's physical characteristics are studied by detecting the debris emanating from the collision region with large particle detectors Heavy-ion collisions at very high energies can produce small short-lived regions of space whose energy density is comparable to that of the 20-micro-second-old universe. This has been achieved by colliding heavy nuclei such as lead nuclei at high speeds, and a first time claim of formation of quark–gluon plasma came from the SPS accelerator at CERN in February 2000. This work has been continued at more powerful accelerators, such as RHIC in the US, and as of 2010 at the European LHC at CERN located in the border area of Switzerland and France. There is good evidence that the quark–gluon plasma has also been produced at RHIC. Thermodynamics The context for understanding the thermodynamics of quark matter is the standard model of particle physics, which contains six different flavors