The New York Times reports that quark stars have been postulated by NASA backed astronomers Jeremy Drake of the Harvard-Smithsonian Center of Astrophysics, and David Helfand of Columbia University. These findings, partly based on archeoastronomy data - the age of a supernova remnent is dated by observations of twelvth century Chinese astronomers then compared to a model that predicts the luminescence at various wavelengths.
Two objects, RXJ1856 and 3C58 have been found to be too cool for their apparent size (3C58) and age (RXJ1856 - as determined archeoastronomically.) This calculation lead the researchers to conclude that there must be a type of matter more dense than packed neutrons - the theoretical stuff of which neutron stars are believed to be made. A material that could be heavier (and thus cooler) than neutrons is made by crushing neutrons into up and down quarks. Theorists then add in some strange quarks to account for charge and density (all very kosher in the parlance of subatomics) and the quark star is born.
A quark star is the latest in the progression of increasing densities in the emerging phase diagram of matter. Phase space, a 2 dimensional space that can be illustrated in simple Cartesian coordinates, is defined by pressure and temperature as the 'x' and 'y' coordinates. Common molecular materials, such as H2O, give rise to a phase diagram at near terrestial conditions, showing the existance of ice, water and steam.
In the same way, the extreme conditions found inside an exploding star - a supernova - can be phase diagramed. The phases at these high energies are more general than the molecular phase diagrams with which most chemists are familiar. Normal matter exists at the temperatures and pressures we all live within. When pressures and temperatures increase to those found within the center of our sun, hydrogen atoms will be pressed together so strongly that the elecrton shell of the atom will break, crushing the neucleii together. As the star fuses it's hydrogen into helium, the star collapses increasing the pressure, and begins to fuse helium. In this way all of the light elements (up to iron) are formed. When a star collapses further it explodes, forming either the rest of the elements or neutronium, the stuff of neutron stars.
If the pressure continues to mount, the neutrons will be crushed, forcing the quarks from all those together.
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