In DepthNuclear Physics

Neutron stars' quark matter not so strange

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Science  18 May 2018:
Vol. 360, Issue 6390, pp. 697
DOI: 10.1126/science.360.6390.697

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For decades, some theoretical physicists have speculated that in the heart of a neutron star, a bizarre type of matter might emerge: a soup of the subatomic particles called quarks. Now, a new analysis indicates the recipe for such "cold quark matter" needs revision. Atomic nuclei consist of protons and neutrons, which themselves consist of trios of particles called up and down quarks, bound tightly by the strong nuclear force. Since the 1970s, some theorists have predicted that under extreme pressures like those in neutron stars, quarks might break free to create a soup of cold quark matter. They also predicted that it should include a third flavor of quarks known as strange quarks. Stable bits of such strange quark matter—or strangelets—might emerge in cosmic rays or linger from violent astrophysical events. Now, a trio of theorists argues that cold quark matter should consist of just up and down quarks. The analysis suggests that particle accelerators on Earth might just be able to produce stable bits of the quark matter. It would also dispel a far-fetched notion the Large Hadron Collider in Switzerland could produce negatively charged strangelets that would gobble up positively charged atomic nuclei—a possibility already ruled out by cosmic ray observation. Up-down quark matter would definitively rule out the doomsday scenario, as it would be positively charged and repel atomic nuclei.