Fermi Spacecraft: 1st to Use Gamma Rays to Identify Pulsars (VIDEO & SOUND)

With NASA's Fermi Gamma-ray Space Telescope, astronomers now are getting their best look at those whirling death stars, the Cheshire Cat Smiles of the universe known as pulsars -.the rapidly spinning and highly magnetized core left behind when a massive star explodes. International teams have analyzed gamma-rays from two dozen pulsars.

Most of the 1,800 cataloged pulsars were found through their periodic radio emissions. Astronomers believe these pulses are caused by narrow, lighthouse-like radio beams emanating from the pulsar's magnetic poles.

The Vela pulsar, which spins 11 times a second, is the brightest persistent source of gamma rays in the sky. Yet gamma rays -- the most energetic form of light -- are few and far between. Even Fermi's Large Area Telescope sees only about one gamma-ray photon from Vela every two minutes. The supernova that created this nebula remnant occurred about 1500 light years away and about 11,000 years ago.

"That's about one photon for every thousand Vela rotations," said Marcus Ziegler, a member of the team reporting on the new pulsars at the University of California, Santa Cruz. "From the faintest pulsar we studied, we see only two gamma-ray photons a day."

Radio telescopes on Earth can detect a pulsar easily only if one of the narrow radio beams happens to swing our way. If not, the pulsar can remain hidden. A pulsar's radio beams represent only a few parts per million of its total power, whereas its gamma rays account for 10 percent or more. Somehow, pulsars are able to accelerate particles to speeds near that of light. These particles emit a broad beam of gamma rays as they arc along curved magnetic field lines.