Astrophysicists at the H.E.S.S. Observatory in Namibia, in which researchers from the University of Warsaw are involved, have discovered the highest energy gamma rays ever from the Vela pulsar. The project at the UW is coordinated by Prof. Tomasz Bulik from the UW Astronomical Observatory. The results of the research have been published in Nature Astronomy.

“Pulsars are the left-over corpses of stars that spectacularly exploded in a supernova. The explosions leave behind a tiny, dead star with a diameter of just some 20 kilometers, rotating extremely fast and endowed with an enormous magnetic field,” Prof. Tomasz Bulik from the UW Astronomical Observatory explains.

The H.E.S.S. team has detected the highest energy gamma rays ever from a pulsar in collaboration with other scientists working at the H.E.S.S. observatory in Namibia. The energy of these gamma rays clocked in at 20 teraelectronvolts, or about ten trillion times the energy of visible light. As the researchers point out, this observation is difficult to reconcile with the theory of the production of such pulsed gamma rays.

The results of the work of astrophysicists have been published in the paper “Discovery of a Radiation Component from the Vela Pulsar Reaching 20 Teraelectronvolts” in the Nature Astronomy journal.

Cosmic lighthouses

“Pulsars emit rotating beams of electromagnetic radiation. They can be compared to cosmic lighthouses. If their beam sweeps across our solar system, we see flashes of radiation at regular time intervals. These flashes, also called pulses of radiation, can be searched for in different energy bands of the electromagnetic spectrum,” Prof. Tomasz Bulik describes.

Researchers think that the source of this radiation is fast electrons that travel from the pulsar’s surface to the very end of its magnetosphere. The magnetosphere is made up of plasma and electromagnetic fields that surround and co-rotate with the star.

The Vela pulsar, located in the Southern sky in the constellation Vela (sail of the ship), is the brightest pulsar in the radio band of the electromagnetic spectrum and the brightest persistent source of cosmic gamma rays in the gigaelectronvolts (GeV) range. It rotates about eleven times per second. Above a few GeV, however, its radiation ends abruptly. Scientists assume that the electrons reach the end of the pulsar’s magnetosphere and escape from it.

Using observations with the H.E.S.S., a new radiation component at even higher energies has been discovered, with energies of up to tens of teraelectronvolts (TeV).

This very high-energy component appears at the same phase intervals as the one observed in the GeV range. To attain these energies, the electrons might have to travel even farther than the magnetosphere, yet the rotational emission pattern needs to remain intact.

The Vela pulsar, apart from its other superlatives, holds the record as the pulsar with the highest-energy gamma rays discovered to date.