The Crab Nebula, the leftovers of a star that went out in a supernova in 1054, is sending out strange signals that scientists can't fully explain. According to research published in the Oct. 7, 2011 issue of the journal Science, astronomers have detected pulsed gamma rays from the neutron star within the nebula that are far higher than the scientists expected.

The pulsed gamma rays have energies between 100 billion and 400 billion electronvolts, far higher than the 25 billion electronvolts previously detected. A 400 billion electronvolt photon is almost a trillion times more energetic than the photons that make up visible light. Explaining this high energy is going to require major adjustments to astronomers' theories of the energy interactions in the nebula.

"The finding shows that the theory is not there yet," said study researcher Henric Krawczynski, a professor of physics at Washington University in St. Louis. "We know less about these systems than we thought."

Best Science Photos of the Week - Oct. 8, 2011