Crab Nebula
This view of the Crab Nebula in visible light comes from the Hubble Space Telescope and spans 12 light-years. The supernova remnant, located 6,500 light-years away in the constellation Taurus, is among the best-studied objects in the sky. NASA

A team of astronomers has spotted gamma ray emissions coming from the Crab Pulsar far higher than theoretical pulsar models can explain.

The inexplicably powerful gamma rays challenge notions of how powerful electromagnetic ways are formed.

The emissions came from the heart of the Crab Nebula, where an extreme object called a pulsar resides. Scientists found emissions at more than 100 gigaelectronvolts (GeV) - 100 billion times more energetic than visible light, says a report published in the journal Science.

"It was totally not expected - it was absolutely jaw-dropping," said Andrew McCann, a Ph.D. candidate at McGill University in Montreal and a co-author of the new study.

"This is one of the hottest targets in the sky, so people have been looking at the Crab Nebula for a long time. Now there's a twist in the tale. High-energy rays coming from the nebula are well-known, but coming from the pulsar is something nobody expected."

The Crab Nebula, which is around 6,500 light-years from Earth, went supernova and exploded in an event which was observed on Earth in 1054. It has since been a constant source of light - so much so that telescopes were trained on it for calibrations.

The Crab pulsar, which is the remains of the original star's core that collapsed in on itself, spins 30 times a second and is so dense it has a greater mass than the sun. It is from this that gamma-rays a million times more energetic than medical X-rays were detected.

"If you asked theorists a year ago whether we would see gamma-ray pulses this energetic, almost all of them would have said no," study co-author Martin Schroedter, of the Harvard-Smithsonian Center for Astrophysics in Cambridge, Mass., said in a statement.

"There's just no theory that can account for what we've found."

Prior to these results, a phenomenon known as curvature radiation - where high-energy charged particles move along a curved magnetic field - was the leading explanation for the Crab's pulsed gamma-ray emissions. But this mechanism cannot account for gamma rays with energies above 100 GeV.

"We thought we understood the gamma-ray emission, and this was really becoming a foundational feature of our models, but that's now thrown out," McCann explained. "The reason why this is so exciting is that it's turning things around in the field."