December 4, 2023

Pulsar sets a new energy record

The Vela pulsar is located 960 light-years away from us and emits very high energy gamma rays. This is shown through observations conducted by a research team at the HESS Observatory in Namibia. Such high-energy radiation from a pulsar has never been measured before. This cannot be explained by previous models of how gamma radiation is produced in pulsars, according to scientists in the journal “Nature Astronomy.”

Once a large star exhausts its primary fuel, it explodes as a supernova. But this explosion does not tear apart the entire star, but only throws the outer layers into space. Depending on its mass, the star’s interior collapses into a black hole or neutron star. Some of these neutron stars rotate rapidly and have a strong magnetic field. It then emits highly concentrated radiation along its north-south axis. But because the axis of the magnetic field is tilted compared to the star’s axis of rotation, the beam sweeps through space similar to the cone of light from a lighthouse and strikes the Earth regularly. There, suitable telescopes detect it as a recurring pulse of radiation – which is why these neutron stars are called “pulsars.”

This is also the case with the Vela pulsar: it rotates about 11 times per second. It emits both radio waves and gamma rays in the gigaelectronvolt range, and is more energetic than the radiation of all other pulsars. Astronomers from the HESS project have been able to observe the pulsar for longer than before using five so-called Cherenkov telescopes, which are specially designed for high-energy radiation from space. They collected gamma radiation from the pulsar for 80 hours. In this way, they were able to detect very rare gamma rays with a power of up to 20 TeV. “This is about two hundred times stronger than all the radiation previously measured from this object,” explains team member Christo Venter from North-West University in South Africa.

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Where does high energy radiation come from?

According to current models, the gamma radiation is caused by the pulsar’s strong magnetic fields that accelerate and deflect electrons. Electrons move outward from the pulsar to the edge of its magnetic field. “On their journey outward, the electrons absorb energy and release it in the form of observed radiation,” says team member Bronek Rudak of the Nicolaus Copernicus Astronomy Center in Poland.

But in order to achieve such high energies, the electrons must be accelerated more strongly. This cannot be reconciled with current models. Researchers believe it is possible that sudden changes in the pulsar’s magnetic field could accelerate the electrons even further. But even this scenario cannot explain high-energy gamma radiation. The research team therefore hopes to solve this mystery through future observations of other high-energy pulsars using more sensitive gamma telescopes.