Artist’s impression of a Bella pulsar with a blue trajectory representing the path of an accelerated particle
DESY Science Communication Lab
Astronomers have discovered extremely high-energy gamma rays being emitted from pulsars. The unusually high energy of this radiation challenges our models about these strange stars and how they accelerate particles.
A pulsar is a rapidly rotating neutron star with a strong magnetic field. Astronomers have discovered thousands of them, but only four are known to emit gamma rays strong enough to be detected by ground-based telescopes. Of these four, only one emits gamma rays, which are made up of photons with energies higher than 1 teraelectronvolt (TeV). This is equivalent to the kinetic energy of a flying mosquito, which is a very large amount of energy for a basic particle. It is called the Bela pulsar.
Arache Jannati Atai Researchers at France’s Paris Cité University have discovered that bela pulsars are even rarer than we thought. They observed the planet through a series of telescopes in Namibia called the High Energy Stereoscopic System and discovered that the planet emits gamma rays with energies exceeding 20 TeV. This is about 20 times more energetic than the highest-energy radiation found from other pulsars.
Current explanations for how pulsars accelerate particles cannot fully explain this. Additionally, the way gamma rays are detected through other particles produced in interaction with Earth’s atmosphere means that they can have even higher energies than Earth’s atmosphere. 20 TeV – We don’t have enough data to know for sure. “We put a lower bound on the energy of the highest-energy particles, which is already difficult for existing models,” says Jannati Atai. “But there is currently no sign of a cutoff energy, even above 20 TeV.”
There are two competing models for photon acceleration by pulsars, both of which involve high-energy electrons colliding with low-energy photons that form gamma rays. The difference is determined by how the electrons are accelerated in the first place. Either they are thrown away from the pulsar by interaction with the magnetic field, or they follow the pulsar’s high-speed rotation and fly around at high speeds. However, it is difficult to reconcile each of these models with these newly discovered gamma rays, which have no apparent upper limit on energy. “The question is where and how the electrons are accelerated,” says Jannati Atai. Until we figure this out, we won’t be able to fully understand pulsars, how they affect their surroundings, and why Bella’s pulsars emit unusually strong radiation.
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