Astronomers have detected pulsed gamma rays from the neutron star at the heart of the Crab Nebula with energies far higher than their theoretical pulsar models can explain.

The emissions were detected by the Very Energetic Radiation Imaging Telescope Array System of four 12-meter Cherenkov telescopes in Arizona. VERITAS, which began collecting full-scale observations in 2007, is used to examine the remains of exploded stars, distant galaxies and powerful gamma-ray bursts and to search for evidence of mysterious dark matter particles.

The study team was led by Nepomuk Otte, a postdoctoral researcher at the University of California, Santa Cruz. The findings are published in Friday's issue of the journal Science.

The Crab Nebula, which is some 6,500 light-years from Earth, was formed when a massive star exploded in a supernova that was observed on Earth in 1054. At the heart of the nebula's colorful layers of gas is a so-called pulsar, the remains of the original star's core that collapsed in on itself into a super-dense, spinning neutron star.

It is most typical for pulsars to be ejected from the stellar wreckage during a supernova. But in the case of the Crab system, the pulsar remained at its center, producing radiation that covers the entire electromagnetic spectrum.

Possible explanations for the Crab pulsar's intense beams have been suggested, but the researchers said much more data will need to be collected before the mechanisms behind these gamma-ray pulses can be better understood.

These are much, much higher energies than had been previously thought can come from a pulsar, Otte said. There is something missing in the models of the cosmic particle accelerators that give rise to the gamma rays, he added. It's a very radical change to the picture of how we believe gamma-ray emission comes from pulsars.

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