Scientists using the H.E.S.S. observatory in Namibia recently made a groundbreaking discovery by detecting incredibly high-energy gamma rays from a pulsar, which is essentially a dead star born from a supernova explosion. These gamma rays had an astonishing energy level of 20 tera-electronvolts, far surpassing the energy of visible light by a staggering 10 trillion times.
Pulsars, the remnants of these explosive events, are incredibly dense, consisting mainly of neutrons. To put it in perspective, a mere teaspoon of pulsar material weighs more than five billion tons, roughly 900 times the mass of the Great Pyramid of Giza.
Pulsars emit beams of electromagnetic radiation, akin to cosmic lighthouses. When these beams intersect our solar system, we observe periodic flashes of radiation, or pulses, across different parts of the electromagnetic spectrum.
Scientists have long believed that fast electrons generated and accelerated within the pulsar’s magnetosphere produce this radiation as they move toward its periphery. The magnetosphere is a region of plasma and electromagnetic fields surrounding the star, rotating with it.
“As these electrons journey outward, they gain energy and emit radiation beams, as we observe,” explains Bronek Rudak, a co-author of the study.
The Vela pulsar, situated in the Vela constellation in the Southern sky, is notable as the brightest pulsar in the radio band and a prominent source of cosmic gamma rays in the giga-electronvolts (GeV) range. However, its radiation diminishes abruptly above a few GeV, presumably as the electrons escape the pulsar’s magnetosphere.
But a new revelation emerged through deep observations with H.E.S.S.: a previously undetected radiation component at even higher energies, reaching tens of tera-electronvolts (TeV).
“This is about 200 times more energetic than any radiation previously recorded from this object,” says co-author Christo Venter from the North-West University in South Africa. This ultra-high-energy component follows the same phase intervals as the one observed in the GeV range. Yet, for electrons to reach such extreme energies, they may need to travel beyond the magnetosphere, while still preserving the pulsar’s rotational emission pattern intact.
“This result challenges our existing understanding of pulsars and demands a reevaluation of how these natural particle accelerators function,” notes Arache Djannati-Atai, who led the research.
The traditional explanation of particles being accelerated along magnetic field lines within or slightly outside the magnetosphere seems insufficient to explain these observations. It’s possible that we are witnessing particle acceleration through a process known as magnetic reconnection beyond the light cylinder, although even this scenario faces difficulties in explaining the origin of such intense radiation.
Regardless of the precise explanation, the Vela pulsar now claims the title of hosting the highest-energy gamma rays ever detected from a pulsar.
“This discovery opens up a new realm for detecting other pulsars with similar high-energy gamma rays, using more sensitive gamma-ray telescopes, which will advance our comprehension of extreme acceleration processes in highly magnetized celestial objects,” adds Djannati-Atai.
Source: Deutsches Elektronen-Synchrotron
