2023-10-10 14:45:07
Scientists from the international observatory HESS (High Energy Stereoscopic System), located in Namibia, have detected a gamma ray emission that is the highest energy of all those emitted by stars of the type known as pulsars. The energy of these gamma rays reached 20 teraelectronvolts. This very powerful emission is difficult to reconcile with the current theory on the production of such pulses of gamma rays. The mystery is served.
A pulsar is the compact corpse of a star annihilated in an explosion of the type known as a supernova. The explosion expels much of the star’s matter into space, but leaves the ultradense core, a stellar corpse that is still very hot and usually has a diameter of a couple of tens of kilometers. This sphere rotates on itself extremely quickly and is endowed with a colossal magnetic field. “These dead stars are made up almost entirely of neutrons and are incredibly dense: a teaspoon of their material has a mass of about 900 times the mass of the Great Pyramid of Giza, as pointed out by Emma de Oña Wilhelmi, a scientist at HESS and of the German Electron Synchrotron (DESY, for its acronym in German), as well as a member of the research team that made and analyzed the detection.
Pulsars emit rotating beams of electromagnetic radiation, projected into the cosmos in a similar way to how a maritime lighthouse projects its light beams into its surroundings. If the beam of a pulsar passes through our solar system, flashes of radiation can be seen from Earth at regular time intervals. These flashes or pulses of radiation can be detectable in different energy bands of the electromagnetic spectrum. The source of this radiation is believed to be electrons produced and accelerated to very high speeds in the pulsar’s magnetosphere, as they travel toward its periphery. The magnetosphere is made up of plasma and electromagnetic fields that surround the stellar corpse and rotate with it.
“On their outward journey, the electrons acquire energy and release it in the form of the observed radiation beams,” explains Bronek Rudak, from the Nicolaus Copernicus Astronomical Center (CAMK PAN) in Poland and co-author of the study.
One possible explanation for the Vela pulsar’s powerful gamma-ray emissions is that infrared photons from the pulsar’s poles are energized into gamma-ray photons (in blue) by ultra-fast electrons. In any case, more research will be necessary before an unequivocal explanation can be offered. (Illustration: Science Communication Lab / DESY)
The Vela pulsar, located in the southern sky, specifically in the constellation Vela (ship’s sail), rotates on itself about eleven times per second.
It is the brightest pulsar in the radio band of the electromagnetic spectrum and the brightest persistent source of cosmic gamma rays in the gigaelectronvolt (GeV) range. Above a few GeV, however, its radiation ends abruptly, presumably because electrons reach the end of the pulsar’s magnetosphere and escape from it.
Strangely, the new observations made with HESS reveal a new component of radiation at higher energies, which are up to 200 times more energetic than all the radiation detected so far from this object, as highlighted by Christo Venter from the University of the North West in South Africa and member of the research team. This very high energy component appears in the same phase intervals as that observed in the GeV range. However, to reach these energies, electrons would have to travel even further from the magnetosphere, although the rotational emission pattern must remain intact.
“This finding challenges our previous knowledge of pulsars and requires a rethinking of how these natural accelerators work,” says Arache Djannati-Atai, from the Laboratory of Astroparticles and Cosmology (APC) in France and a member of the research team.
Whatever the explanation, the Vela pulsar now officially holds the record as the most powerful gamma ray emitter of all pulsars.
The study is titled “Discovery of a Radiation Component from the Vela Pulsar Reaching 20 Teraelectronvolts.” And it has been published in the academic journal Nature Astronomy. (Source: NCYT from Amazings)
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