Discovery of new star
type may defy fundamental physics
By PAUL RECER, AP Science Writer
WASHINGTON (April 10, 2002 3:56 p.m.
EDT) — A pair of bizarre objects found by an orbiting X-ray telescope may
represent a new class of star and may contain a new form of matter, defying
current theories of particle physics and astronomy.
Observations of the objects, called
RXJ1856 and 3C58, found they were too small and too cold to fit the pattern of
neutron stars, which are collapsed, very dense stars composed of neutrons, an
extremely heavy, elemental particle.
At a news conference Wednesday,
astronomers announced that RXJ1856 has a temperature of about 1.2 million
degrees, too cool for a neutron star, and a diameter of about 12 miles, too
small to fit the standard model for neutron stars.
This evidence "points to a star
composed not of neutrons, but of quarks in a form known as strange quark
matter," said Jeremy Drake of the Harvard-Smithsonian Center for
Astrophysics, the lead researcher for the RXJ1856 observations.
Quarks are elemental particles that
make up a neutron. The quarks in an ordinary neutron are of two types — up and
down. Drake said that data from the X-ray telescope suggests that RXJ1856 is
composed of up and down quarks, plus another particle called a strange quark.
Strange quarks are much denser than
up or down quarks. The group of quarks could have evolved from neutrons that
were collapsed by the extreme density and mass of the star, Drake said.
A team led by David Helfand of
Columbia University observed 3C58, the neutron star remnant of a famous
supernova, or exploded star, and found that its temperature was less than 1.8
million degrees, far below the predicted value for a neutron star.
This cool temperature, said Helfand,
violates the standard theory for neutron stars and raises fundamental questions
about the matter in 3C58.
"It appears that neutron stars
aren't pure neutrons after all — new forms of matter are required," said
Michael Turner, an astrophysicist at
the University of Chicago, said the two observations suggest the objects
"may be new members of the stellar family tree."
He said they appear to be less dense
than black holes or white dwarfs, two other exotic objects in the universe, but
are clearly different than neutron stars.
"It is possible that all of the
stars we call neutron stars may be strange stars" such as those observed by
Drake and Helfand, said Turner. He said, however, that the observations will
have to confirmed by others.
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