PHYSICS NEWS UPDATE The American Institute of Physics Bulletin of Physics News Number 760 January 3, 2006 by Phillip F. Schewe, Ben Stein
HOW DOES MATTER TERMINATE? That is, at the microscopic level how does nature make the transition from a densely packed material surface (the skin of an apple, say) to the nothingness that lies above? This issue is especially dramatic for collapsed stars, where the matter density gradient marking the star-to-vacuum transition can be as great as 10^26 g/cm^4. A new model, proposed by physicists at Los Alamos and Argonne National Labs, claim that the prevailing theory of what happens at quark-star surfaces is wrong. These quark stars are characterized by interiors which consist of quark matter from the center all the way to the surface. For quark matter to exist in the low pressure environment near the surface, matter containing nearly equal numbers of up, down and strange quarks must be preferred over neutrons and protons. Theorists have speculated about this possibility (often called the Strange Quark Matter Hypothesis) since the early 1980's. A star made in this way, a quark star, is thought to be the densest possible type of matter. Any denser than this, and the star must become a black hole. In the ordinary kind of matter prevailing in our solar system, matter consists of up (u) and down (d) quarks. A proton, for example, consists of two u quarks and one d quark. A neutron consists of two d quarks and one u quark. Converting u or d quarks to strange (s) quarks in neutrons or protons is typically unstable. In the high-density environment of quark stars, however, matter containing up, down, and strange quarks might be stable. The reason for this is that when thousands of quarks are together (unlike the ordinary twosome or threesome quark combinations we see on Earth in the form of protons, neutrons, and mesons) u-d-s matter is likely to be a more energy-efficient form of packaging than the u-d form of matter we have on our planet if the strange quark matter hypothesis is correct. This process really comes into play in collapsed stars, where strange quarks could roughen the surface of the stars. Such a surface, says Los Alamos scientist Andrew Steiner ([EMAIL PROTECTED], 505-667-0673), can be compared to a liquid surface. On Earth liquid surfaces are generally flat. Because of surface tension, too much energy would be required to overcome the tension and form additional facets above the surface. At a quark star, by contrast, surface tension may not be large and the crust of the star could form extra surfaces, nugget-like objects without any undue energy cost. The positively charged quark lumps would be surrounded by a sea of electrons, as required to make the crust electrically neutral (see figure at http://www.aip.org/png/2006/245.htm ). Where did the electrons come from? They're left over from the atoms that were crushed in the collapse phase; some electrons are pressed into protons to make neutrons, but some would have survived. What would be the test of the hypothesis of an inhomogeneous termination at a quark-star surface? Again, the Los Alamos group is at odds with the prevailing model, which says that quark stars should be more luminous than neutron stars. Au contraire, they say. Just as foam on the surface of a water surface clouds our view into the water, so the quark bumps on an otherwise smooth surface at a quark star would enhance the scattering of photons and neutrinos, lowering the quark star's luminosity. (Jaikumar et al., Physical Review Letters; movie at http://t16web.lanl.gov/?section=highlights ) ART IN CRYSTALLOGRAPHY. Devoted to the amazing symmetries of atoms and the beautiful complex structures of molecules, crystallography has always had a naturally artsy side. Now the American Crystallographic Association (ACA) has begun an annual contest encouraging individuals to submit visual art depicting crystallography topics and explaining them in a caption. The winner of the inaugural competition, David Goodsell of Scripps, created "Blood 2,000,000X," a watercolor that reveals Y-shaped antibodies, UFO-resembling cholesterol molecules, and other well-known compounds in the vicinity of a red blood cell. Other entries included 'Poliovirus," a sculpture of the paralyzing pathogen's protein coat attaching to a receptor; and "Fracture," a mosaic of crystallized tuberculosis bacteria fracturing in a gel. Additional entries had titles such as "24 Detergents Upside Down," "Be Fruitful and Symmetrize," and "H to D Tango" (where H stands for hydrogen and D for deuterium). ACA plans to continue the competition at its upcoming meetings. (Images at http://www.aip.org/png/2005/244.htm; more entries and details at the Art in Crystallography website, http://www.hwi.buffalo.edu/ACA/HotNews/ArtEntries2005.htm) *********** PHYSICS NEWS UPDATE is a digest of physics news items arising from physics meetings, physics journals, newspapers and magazines, and other news sources. It is provided free of charge as a way of broadly disseminating information about physics and physicists. For that reason, you are free to post it, if you like, where others can read it, providing only that you credit AIP. Physics News Update appears approximately once a week. AUTO-SUBSCRIPTION OR DELETION: By using the expression "subscribe physnews" in your e-mail message, you will have automatically added the address from which your message was sent to the distribution list for Physics News Update. If you use the "signoff physnews" expression in your e-mail message, the address in your message header will be deleted from the distribution list. 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