Domingo 28 de Abril de 2002, Ip nš 13

Strange stars suggest new kind of matter
Por Richard Stenger

Two rogue stars have failed to live up to scientific expectations, compelling puzzled astronomers to consider the likelihood that they possess a new and exotic form of matter.

If confirmed, the discovery would warrant a new class of objects, quark stars, which fall somewhere in between neutron stars and black holes in density.

"It would change the family tree a bit and put a new member in it," University of Chicago astronomer Michael Turner told reporters Wednesday.

Neutron stars are the vestiges of immense supernova explosions, collapsed stars with extremely compact cores, denser than all known objects except black holes. A teaspoonful of a neutron star would weigh one billion tons, as much as all the cars and trucks on Earth.

At least, until astronomers using the Chandra X-ray Observatory spied two presumed neutron stars, RXJ1856 and 3C58. Based on the known laws of physics, the former appeared much smaller and the latter much colder than they should.

The strange traits of RXJ1856 and 3C58 suggest that the pair are not neutron stars at all. They could be composed of quarks, or crystals of sub-nuclear particles rather than neutrons.

"Both of these objects have properties which seem to contradict what we know about matter," said Harvard-Smithsonian astronomer Jeremy Drake.

Quarks are thought to be the fundamental building blocks of matter. They combine to make the basic subatomic particles, protons and neutrons.

But quarks have remained fleeting, appearing for a fraction of a second in a handful of laboratories when atomic nuclei smash into one another at incredible speeds.

The quarks that make up conventional matter are called "up" and "down" quarks. Physicists theorize that even more elusive "strange" quarks, possible remnants from the birth of the universe, still lurk in the cosmos.

The Chandra data gives the first evidence that they exist in nature. But the astronomers caution that the results are preliminary.

"More observations are needed to find out what is going on here," Turner said.

  10/04/2002. CNN.