The Crab Nebula is one of the most studied supernova remnants and yet it is still guarding some of its secrets. Well, for now. Swedish researchers have used a telescope on an atmospheric balloon to peer right into its core and understand how the powerful X-ray flares it emits are produced.
As explained in Scientific Reports, the X-ray flares appear to come from a compact region close to the pulsar, a type of neutron star. The observations suggest that a donut-shaped magnetic field could be the source of the flares.
“Our measurements indicate that the X-rays come from an organized region in the vicinity of the pulsar at the centre of the nebula," lead author Mark Pearce, from the KTH Royal Institute of Technology, said in a statement. "Electrons gyrating around magnetic field lines in this region produce the X-rays. The measurements are made in an unexplored energy range, so they provide new information which will help to solve the puzzle of how high energy radiation is generated.”
To discover the X-ray producing region, the team looked at the polarization of its light. Photons in polarized light oscillate all in the same direction and there are only a few ways for astrophysical sources to create them. What they saw appears to be consistent with the magnetic field scenario they modeled.
Pulsars – and neutron stars, in general – are complex objects and there’s still much we need to understand about them. They are the product of supernova explosions when the star is not quite massive enough to form a black hole. The supernova that created the Crab Nebula was actually observed in 1054 CE and recorded by Chinese astronomers.
“Neutron stars are fascinating objects,” Pearce explained. “The Crab pulsar rotates around an axis 30 times per second producing flashes of X-rays – a sort of cosmic lighthouse. The X-rays arise from the acceleration of electrons in intense magnetic fields (10 trillion times stronger than the Earth’s magnetic field), up to energies typically a hundred times higher than obtainable at the LHC accelerator.”
The observations were possible thanks to the PoGO+ telescope, which was designed by the KTH Royal Institute of Technology with the specific objective of studying the Crab Nebula and Cygnus X-1, a stellar black hole. Last summer, the telescope was attached to a balloon and was lifted to an altitude of 40 kilometers (25 miles) where it observed the two sources for six days before safely coming back down to Earth.