High-Energy Gamma-Ray Emission from Vela Pulsar Sparks New Insights in Pulsar Physics

Astronomers have spotted the highest-energy outburst of light from a pulsar ever seen. The discovery could indicate new physics around these incredibly dense, rapidly spinning dead stars.

The team, including scientists from France's National Center of Scientific Research (CNRS), made observations of the Vela pulsar — which, at 1,000 light-years from Earth, is one of the closest pulsars ever detected — with the four telescopes that make up the gamma-ray-hunting High Energy Stereoscopic System (HESS).

This revealed the gamma-ray output of the Vela pulsar to be around 200 times more powerful than that of average pulsars. The results are described in a paper published Oct. 5 in the journal Nature Astronomy.

"We have discovered gamma-ray photons reaching 20 tera electron volts (TeV) from the Vela pulsar," study co-author Arache Djannati-Ataï, a CNRS researcher, told Live Science via email. "These are the highest-energy gamma rays ever detected from a pulsar."

Pulsars like Vela are neutron stars born when massive stars reach the ends of their lives, exhausting the fuel for nuclear fusion at their cores. Unable to support themselves against their own gravity, the cores of these stars collapse while a massive amount of outer stellar material blows away in a supernova explosion.

This results in an object with a mass between one and two times that of the sun crammed into the width of an average city  —  around 12 miles (20 kilometers). Because a dying star becomes so much smaller when collapsing, many neutron stars spin much faster than their progenitors, like a figure skater drawing in their arms to spin faster, with some neutron stars spinning up to 700 times per second.

The Vela pulsar is one of the best-studied spinning neutron stars and is an example of the extreme nature of these objects. Created in a supernova around 10,000 years ago, the neutron star has a width of around 12 miles and completes 11 rotations per second  —  faster than the blades of a helicopter.

Neutron stars also have some of the most powerful magnetic fields in the known universe. These magnetic fields channel matter like electrons and positions, accelerating them to near light speeds. This creates jets of particles, which generate two opposing light cones that blast out from the poles of younger neutron stars. When those light cones sweep over Earth at regular intervals as the neutron star spins, we call the object a pulsar.

Radiation in these cones comes in a variety of forms, from low-energy radio waves to high-energy gamma-rays that can be spotted from Earth using a variety of telescopes. Yet gamma-rays of such high energy have never been seen coming from a pulsar before.

This indicates that something unexpected is happening around the Vela pulsar and its polar jets, which have been seen to stretch as far as 0.7 light-years  —  about 15 million times the distance between Earth and the moon.

Djannati-Ataï explained that standard light cones are not thought to be wide enough to accelerate particles to the staggering energies observed around Vela. Thus, the team suggested several possibilities for the new powerful gamma-ray emission mechanism.

It's possible that particles are being accelerated outside the standard light-cone zones around pulsars, or that well-structured magnetic fields exist beyond these standard acceleration zones. Alternatively, the team theorizes that the bulk movement of winds from neutron stars could be accelerating the particles and their emissions.

Djannati-Ataï said the team was very surprised by the detection and will now investigate if even higher-energy emissions are coming from this cosmic lighthouse. They also intend to use the HESS observatory, located in Namibia, to search for high-energy gamma-ray emissions around other relatively close pulsars.

"We know we have a first of a kind at hand, which shall help update our models of pulsar emission," Djannati-Ataï said. "Understanding better the acceleration and emission processes in pulsars will possibly have implications on our understanding of other highly magnetized astrophysical objects, such as black hole magnetospheres."


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