The new gammarayonly pulsarsput that idea to rest

5, 2009, with a two-year, three-month base period,followed by three two-year options that may be exercised at NASA's discretion.It is a firm-fixed price contract with a value of approximately $108 million,if all options are exercised. The contract is a follow-on effort for agency-wide conferencing servicesawarded under the General Services Administration's Networx Universalcontract.For information about NASA and agency programs, visit: http:// SOURCENASASonja Alexander, Headquarters, Washington, 1-202-358-1761,, or Angela Storey, Marshall Space Flight Center,Huntsville, Ala., 1-256-544-0034, , both of NASA. GREENBELT, Md., Jan. 6 /PRNewswire-USNewswire/ NASA's Fermi Gamma-ray SpaceTelescope has discovered 12 new gamma-ray-only pulsars and has detectedgamma-ray pulses from 18 others. The finds are transforming our understandingof how these stellar cinders work.

(Logo: http://)"We know of 1,800 pulsars, but until Fermi we saw only little wisps of energyfrom all but a handful of them," says Roger Romani of Stanford University,Calif. "Now, for dozens of pulsars, we're seeing the actual power of thesemachines."A pulsar is a rapidly spinning and highly magnetized neutron star, the crushedcore left behind when a massive sun explodes. Most were found through theirpulses at radio wavelengths, which are thought to be caused by narrow,lighthouse-like beams emanating from the star's magnetic poles. If the magnetic poles and the star's spin axis don't align exactly, thespinning pulsar sweeps the beams across the sky.

Radio telescopes on Earthdetect a signal if one of those beams happens to swing our way. "That has colored our understanding of neutron stars for 40 years," Romanisays. The radio beams are easy to detect, but they represent only a few partsper million of a pulsar's total power. Its gamma rays, on the other hand,account for 10 percent or more. "For the first time, Fermi is giving us anindependent look at what heavy stars do," he adds Pulsars are phenomenal cosmic dynamos.

Through processes not fully understood,a pulsar's intense electric and magnetic fields and rapid spin accelerateparticles to speeds near that of light. Gamma rays let astronomers glimpse theparticle accelerator's heart. "We used to think the gamma rays emerged near the neutron star's surface fromthe polar cap, where the radio beams form," says Alice Harding of NASA'sGoddard Space Flight Center in Greenbelt, Md. "The new gamma-ray-only pulsarsput that idea to rest." She and Romani spoke today at the AmericanAstronomical Society meeting in Long Beach, Calif.Astronomers now believe the pulsed gamma rays arise far above the neutronstar. Particles produce gamma rays as they accelerate along arcs of openmagnetic field. For the Vela pulsar, the brightest persistent gamma-ray sourcein the sky, the emission region is thought to lie about 300 miles from thestar, which is only 20 miles across.Existing models place the gamma-ray emission along the boundary between openand closed magnetic field lines.