X-ray emissions from the stars suggest they contain quarks -- elementary nuclear particles that so far have eluded attempts by physicists to appear in high-energy particle accelerator experiments -- and other subatomic entities that only have existed for fleeting moments in laboratories.
"Nature has carried out an experiment that we cannot yet duplicate on Earth," said University of Chicago physicist Michael Turner.
If the analysis is correct, the studies made using the Chandra X-ray Observatory would be a fundamental discovery in physics.
"It contradicts ideas of how nature behaves in the tiniest of details," said Jeremy Drake, with the Harvard-Smithsonian Center for Astrophysics in Cambridge, Mass., and the lead author of a paper on one of the objects, called RX J1856, which is scheduled for publication this month in The Astrophysical Journal.
The star, which is located about 400 light years from Earth, is a relatively near, relatively bright neutron star that also has been imaged in optical light by ground-based observatories and in the ultraviolet by the Hubble Space Telescope. Those images were used to help determine the star's distance from Earth and its size.
Neutron stars are believed to be the collapsed cores of gigantic stars that can pack the mass of the sun into a space the size of the Grand Canyon. The pressure and density inside these objects, which range in size from 12 miles to 20 miles in diameter, converts regular matter -- comprised of electrons, protons and neutrons -- almost entirely into neutrons by breaking bonds inside the atoms' nuclei. A teaspoonful of neutron star material weighs a billion tons.
Drake's team, however, found that RXJ1856, a star discovered first in 1996 by another X-ray telescope, may be too small to be a neutron star.
"It turns out to be only 5- to 10 miles in size," said Drake. "We see immediately that there is a big problem because it is too small to be explained by the smallest of neutron stars."
While acknowledging the star simply could have an undetected hot spot of X-ray emissions, Drake's team suggests instead the neutrons inside RXJ1856 have broken down into even more base particles to create what is called strange quark matter.
In addition, evidence from another neutron star that appears to be too cool to account for its age and density supports Drake's theory by postulating that subatomic particles related to quarks are inside the second star's core, said David Helfand, an astronomer at Columbia University.
"Our observations offer the first compelling test of models for how neutron stars cool and, the standard theory fails," said Helfand. "It appears that neutron stars aren't pure neutrons after all -- new forms of matter are required."
(Reported by Irene Brown at Cape Canaveral, Fla.)