The discovery that the Crab Pulsar is emitting the highest-energy gamma rays ever detected has prompted researchers to consider new theories about gamma-ray production and probe deeper into the mystery surrounding cosmic rays.
Astrophysicists found recently that high-energy pulsed gamma rays were being emitted from the neutron star at the heart of the Crab Nebula, a finding that baffled scientists and defied the principles of current theoretical pulsar models.
Scientists have said that the highly energized gamma rays are coming from an extreme object, known as a pulsar, at the Crab Nebula's center and that the rays have energies exceeding 100 billion electron- volts, higher energy levels than the current theoretical models can explain.
The emissions were detected by VERITAS (Very Energetic Radiation Imaging Telescope Array System) at the Fred Lawrence Whipple Observatory in Arizona. VERITAS is a ground-based observatory for gamma-ray astronomy, which began collecting full-scale observations in 2007. It 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 Crab Pulsar is considered among the best understood systems in all of astronomy, yet here we have found something totally new ... It is astronomy in a completely new light; we are seeing phenomena that you just can't explore with optical light or X-rays, or even low-energy gamma rays, said Rene Ong, a UCLA professor of physics and astronomy and spokesperson for the VERITAS collaboration at the Harvard–Smithsonian Center for Astrophysics, according to TG Daily.
If you asked theorists a year ago whether we would see gamma-ray pulses this energetic, almost all of them would have said, 'No.' There's just no theory that can account for what we've found, said corresponding author Martin Schroedter of the Harvard-Smithsonian Center for Astrophysics (CfA).
Located some 6,500 light-years from Earth, the Crab Nebula was formed when a massive star exploded in a supernova. 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.
Commenting that it is a completely new and surprising phenomenon for pulsars, Ong said the new findings may throw light on the mysteries surrounding cosmic rays.
We are bombarded by high-energy particles from all over the cosmos that reach unimaginable energies ... These cosmic rays are an important energy source in our galaxy, yet we have no clue where they are coming from, said Ong.
The study was led by University of California postdoctoral researcher Nepomuk Otte. The findings were published last week in Science.
The new findings puzzled scientists. Earlier, a phenomenon known as curvature radiation - where high-energy charged particles move along a curved magnetic field - had helped explain the Crab's pulsed gamma-ray emissions. But this mechanism cannot account for gamma rays with energies above 100 GeV.
After many years of observations and results from the Crab, we thought we had an understanding of how it worked, and the models predicted an exponential decay of the emission spectrum above around 10 GeV. So it came as a real surprise when we found pulsed gamma-ray emission at energies above 100 GeV, said the study's co-author, David Williams, an adjunct professor of physics at UC.