New Method Used For Probing Pulsars

2-10-96
Baltimore -- Astronomers using a new method for probing rapidly spinning neutron stars known as pulsars, made possible by the Hubble Space Telescope, have revealed unexpected nonthermal radiation coming from a middle-aged pulsar and, for the first time, have measured the surface temperatures of two old pulsars.

The method, which allows astronomers to detect emissions from these stars in optical and ultraviolet wavelengths, also revealed that an unexplained heating mechanism is operating deep inside the oldest neutron stars in the study.

Dr. France Cordova, chief scientist at the National Aeronautics and Space Administration and professor of astronomy and astrophysics at Penn State, will discuss these discoveries at a press briefing and a topical lecture during the annual meeting of the American Association for the Advancement of Science on Saturday, February 10.

The press briefing will take place at 10:00 a.m. in the Sheraton Inner Harbor Hotel (Potomac Room, level 3). The topical lecture, titled "All Eyes on the Universe: Multiwavelength Astrophysics," will take place at 1:00 p.m. in the Baltimore Convention Center (room 309).

"I will discuss the novel ways in which we used the Hubble, the results, and their implications," she says. The research, which was done by Cordova and her colleagues at Penn State, George Pavlov, visiting professor, and Guy Stringfellow, postdoctoral fellow, has been submitted for publication in The Astrophysical Journal.

Astronomers have used the unusual properties of pulsars to test Einstein's theory of relativity and to discover the first planets ever found outside our solar system. But previous research on pulsar emissions have studied mainly radio, X-ray, or gamma-ray wavelengths.

"We needed the crystal vision of the Hubble Space Telescope to detect the optical and ultraviolet counterparts of radio pulsars because emissions at these wavelengths from these objects are predicted to be fainter than could be resolved using ground-based telescopes," Cordova explains.

Cordova's team was attempting to confirm a hypothesis about the unknown interior of neutron stars, where matter is pushed to extremes of gravitational forces and magnetic fields.

"Thirty years after the discovery of neutron stars, we still do not know the properties of the superdense matter in their cores and cannot fully explain how they radiate in all wavelengths," she says.

When Cordova's team combined their results for the neutron stars in all wavelengths, they found the emission from the youngest one was "non-thermal in character," whereas the oldest were much hotter than predicted.

"The relatively high temperature means some kind of heating or reheating mechanism has to be operating inside old neutron stars -- otherwise they would have cooled down -- but we do not yet adequately understand the source of this heat," Cordova says. "What we need now are further observations of neutron stars with the Hubble Space Telescope to help drive the development of a theory that will adequately explain the properties of these puzzling objects." she says.

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EDITORS: France Cordova can be contacted at (202) 358-1809, or George Pavlov is at (814) 865-9482.

Contacts:
Barbara Kennedy
(814) 863-4682 (office)
(814) 237-0661 (home)
bkk1@psuvm.psu.edu

Vicki Fong
(814) 865-9481 (office)
(814) 238-1221 (home)
vyf1@psu.edu