Quark stars point to new matter

RX J1856.5-3754: Its size, just 11 km across, and temperature profile mean it cannot be a neutron star

Wednesday, 10 April, 2002

Astronomers believe they have found their first quark stars - super-dense objects that are formed when the remnants of old stars collapse in on themselves.Theorists have long suspected the existence of these weird objects, which are denser than neutron stars but are not compact enough to become black holes.The observations were made by the orbiting Chandra X-ray Observatory, and were unveiled at an American space agency (Nasa) press briefing in Washington, US.Quarks are incredibly tiny particles and make up much of the Universe. But on Earth, they are impossible to find on their own - they huddle together in groups of three, making up the protons and neutrons inside ordinary atoms.Knowledge of their existence is known from experiments in giant accelerator machines. Quarks are seen fleetingly in the debris from atoms that have been smashed together at very high speeds.

Strange threat:

But theory has long suggested that inside the superdense remains of dead stars, quarks might be forced out permanently into the open.They would make up a radically different state of matter called strange quark matter, so dense that a teaspoonful of it would weigh billions of tonnes.Now, astronomers say they have found two objects in space - one too small and one too cold - that defy "our understanding of the structure of matter". The Chandra researchers say these objects can only be understood if they consist of strange quark matter.Such quark stars are not dense enough to be black holes, but they are too dense to be anything else.The astronomers caution that further observations are needed to confirm their findings, but say that if they are right, quark stars will provide stunning insights into the nature of matter.Some scientists have suggested that if strange quark matter does exist, it could destroy ordinary matter by converting protons and neutrons to naked quarks, spreading through space like a cosmic wildfire.Now they know where to look, researchers will be able to judge what the chances are of this strange threat ever materialising.