Scientists utilizing the H.E.S.S. observatory in Namibia have identified the most energetic gamma rays ever recorded from a pulsar, a type of dead star.
Clocking in at a staggering 20 tera-electronvolts, these gamma rays possess energy approximately ten trillion times greater than that of visible light. These observations present a challenge to existing theories concerning the genesis of such intense pulsed gamma rays.
Pulsars are remnants of stars that have undergone a massive explosion termed a supernova. This cataclysmic event leaves behind a minuscule, dead star, roughly 20 kilometers in diameter, spinning at incredible speeds and possessing a potent 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,” explained H.E.S.S. scientist Emma de Oña Wilhelmi.
Resembling cosmic lighthouses, pulsars emit rotating beams of electromagnetic radiation. When these beams pass through our solar system, we witness regular intervals of radiation flashes.
Scientists believe that the origin of this radiation is the swift electrons that are generated and propelled in the pulsar’s magnetosphere as they move toward its outer boundary. The magnetosphere, filled with plasma and electromagnetic fields, revolves with the star.
“On their outward journey, the electrons acquire energy and release it in the form of the observed radiation beams,” said Bronek Rudak from the Nicolaus Copernicus Astronomical Center (CAMK PAN) in Poland.
Located in the Southern sky within the Vela constellation, the Vela pulsar is notably the most radiant pulsar in the radio band of the electromagnetic spectrum.
It also stands as the brightest continuous cosmic gamma-ray source in the giga-electronvolts (GeV) range, with a rotation frequency of around eleven times every second.
However, its radiation abruptly halts beyond a few GeV, presumably when electrons surpass the magnetosphere’s confines.
Now, thanks to in-depth observations with H.E.S.S., a previously undetected radiation component of even higher energies has emerged, peaking at tens of tera-electronvolts (TeV).
“That is about 200 times more energetic than all radiation ever detected before from this object,” said Christo Venter from the North-West University in South Africa.
Interestingly, these ultra-high-energy emissions appear in the same intervals as those observed in the GeV range. But to achieve such intensities, electrons might journey beyond the magnetosphere, even as the rotation emission pattern persists.
“This result challenges our previous knowledge of pulsars and requires a rethinking of how these natural accelerators work,” said Arache Djannati-Atai from the Astroparticle & Cosmology (APC) laboratory in France, who led the research.
“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.”
Regardless of this mystery, the Vela pulsar now holds the distinction of emitting the most energetic gamma rays observed to date.
“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,” said Djannati-Atai.
The study is published in the journal Nature Astronomy.
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