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Gamma Rays from a Pulsar with the Highest Energy Ever

Scientists have discovered the highest energy gamma rays ever from a dead star known as a pulsar using the H.E.S.S. observatory in Namibia. These gamma rays had an energy of 20 tera-electronvolts, which is roughly ten trillion times that of visible light. According to the global team’s research published in the journal Nature Astronomy, this finding is difficult to explain in terms of the hypothesis for the origin of such pulsed gamma rays.

The researchers think that infrared light particles (photons) from the poles of the pulsar are boosted to gamma-ray energies (blue) by fast electrons. Image Credit: Science Communication Lab for DESY

The remains of stars that spectacularly erupted in a supernova are known as pulsars. The remnants of the explosions are a dead, small star with a diameter of about 20 km that rotates exceedingly quickly and has a powerful magnetic field.

These dead stars are almost entirely made up of neutrons and are incredibly dense: a teaspoon of their material has a mass of more than five billion tons, or about 900 times the mass of the Great Pyramid of Giza.

Emma de Oña Wilhelmi, Study Co-Author and Scientist, H.E.S.S Observatory

Pulsars release rotating beams of electromagnetic radiation, similar to cosmic lighthouses. When their beam sweeps throughout the universe, flashes of radiation at regular intervals can be observed. These flashes, also known as bursts of radiation, can be seen in many energy bands of the electromagnetic spectrum.

Scientists believe that the source of this radiation is fast electrons created and accelerated in the pulsar’s magnetosphere as they migrate toward its perimeter. The magnetosphere is made up of plasma and electromagnetic fields that encircle and spin with the star.

On their outward journey, the electrons acquire energy and release it in the form of the observed radiation beams.

Bronek Rudak, Study Co-Author, Nicolaus Copernicus Astronomical Center

The Vela pulsar, located in the constellation Vela (ship’s sail), is the brightest pulsar in the electromagnetic spectrum’s radio band and the brightest persistent emitter of cosmic gamma rays in the giga-electronvolt (GeV) range. It rotates around eleven times each second. However, at a few GeV, its radiation abruptly ceases, likely because electrons reach the pulsar’s magnetosphere and flee.

However, this is not the end of the story: utilizing extensive observations with H.E.S.S., a new radiation component at even higher energies, with energy of up to tens of tera-electronvolts (TeV), has now been detected.

That is about 200 times more energetic than all radiation ever detected before from this object.

Christo Venter, Study Co-Author, North-West University

This very high-energy component emerges at the same phase intervals as the GeV component. To achieve this energy, electrons might have to travel even farther than the magnetosphere, but the rotating emission pattern must be preserved.

Arache Djannati-Atai from the Astroparticle & Cosmology (APC) laboratory in France, who led the research, added, “This result challenges our previous knowledge of pulsars and requires a rethinking of how these natural accelerators work. The traditional scheme according to which particles are accelerated along magnetic field lines within or slightly outside the magnetosphere cannot sufficiently explain our observations. Perhaps we are witnessing the acceleration of particles through the so-called magnetic reconnection process beyond the light cylinder, which still somehow preserves the rotational pattern? But even this scenario faces difficulties to explain how such extreme radiation is produced.

Whatever the answer, the Vela pulsar currently holds the record for having the highest-energy gamma rays detected to date, in addition to its other accolades.

Djannati-Atai added, “This discovery opens a new observation window for detection of other pulsars in the tens of teraelectronvolt range with current and upcoming more sensitive gamma-ray telescopes, hence paving the way for a better understanding of the extreme acceleration processes in highly magnetized astrophysical objects.”

Scientists discover the most energetic gamma rays from a pulsar ever

Video Credit: Deutsches Elektronen-Synchrotron

Journal Reference

The H.E.S.S. Collaboration, et al. (2023) Discovery of a radiation component from the Vela pulsar reaching 20 teraelectronvolts. Nature Astronomy. doi:10.1038/s41550-023-02052-3.

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