WASHINGTON - Two 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 yesterday, 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 Helfand.

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.