Earth has been hit by a blast from a dead star so energetic that scientists cannot explain it.
The burst of gamma rays, originating in a dead star known as a pulsar, is the highest energy of its kind ever seen. It was equivalent to about ten trillion times the energy of visible light, or 20 tera-electronvolts.
Scientists are unable to explain exactly what kind of a scenario could lead a pulsar to emit such intense energy, and the researchers behind the breakthrough say that it “requires a rethinking of how these natural accelerators work”.
Scientists hope that they can find yet more powerful energy blasts from pulsars, with a view to better understanding how they are formed.
Pulsars are formed when a star dies, exploding in a supernova and leaving behind a tiny, dead star. They are just 20 kilometres across, and spin extremely fast with a powerful magnetic field.
“These dead stars are almost entirely made up of neutrons and are incredibly dense: a teaspoon of their material has a mass of more than five billion tonnes, or about 900 times the mass of the Great Pyramid of Giza,” said Emma de Oña Wilhelmi, a scientist at the High Energy Stereoscopic System observatory in Namibia that detected the blast.
As pulsars spin, they throw out beams of electromagnetic radiation, throwing it out like a cosmic lighthouse. That means that someone in one spot – like the Earth – will see the radiation pulses flash in a regular rhythm as they spin past.
The radiation is thought to be the result of fast electrons that are produced and thrown out by the the pulsar’s magnetosphere, which is made up of plasma and electromagnetic fields that surround the star and spin with it. Scientists can search the radiation for different energy bands within the electromagnetic spectrum, helping them understand it.
When scientists previously did that with the Vela pulsar examined in the new study, they found that it was the brightest everseen in the radio band, and the brightest persistent source in the giga-electronvolts. But the new research found that there is a part of the radiation with even more high energy components.
“That is about 200 times more energetic than all radiation ever detected before from this object,” said co-author Christo Venter from the North-West University in South Africa. Scientists don’t know exactly how that could happen.
“This result challenges our previous knowledge of pulsars and requires a rethinking of how these natural accelerators work,” says Arache Djannati-Atai from the Astroparticle & Cosmology (APC) laboratory in France, who led the research. “The traditional scheme according to which particles are accelerated along magnetic field lines within or slightly outside the magnetosphere cannot sufficiently explain our observations.
“Perhaps we are witnessing the acceleration of particles through the so-called magnetic reconnection process beyond the light cylinder, which still somehow preserves the rotational pattern? But even this scenario faces difficulties to explain how such extreme radiation is produced.”
An article describing the findings, ‘Discovery of a Radiation Component from the Vela Pulsar Reaching 20 Teraelectronvolts’, is published today in the journal Nature Astronomy.