Pulsar surprises astronomers with record-breaking gamma-rays

Artist's impression of the Vela pulsar, in the center, and its magnetosphere, whose edge is marked by the bright circle. The blue tracks travelling outwards represent paths of accelerated particles. These produce gamma radiation along the arms of a rotating spiral by colliding with infrared photons emitted in the magnetosphere (in red).
Artist's impression of the Vela pulsar, in the center, and its magnetosphere, whose edge is marked by the bright circle. The blue tracks travelling outwards represent paths of accelerated particles. These produce gamma radiation along the arms of a rotating spiral by colliding with infrared photons emitted in the magnetosphere (in red). (Image credit: Science Communication Lab for DESY)

Nearly 1,000 light-years from where you're sitting lies a spinning, highly magnetized neutron star that is so dense, a tablespoon of it equals something like the weight of Mount Everest. It's an intense sight, to say the least, which is why astronomers naturally love studying it. You might've even heard its name uttered before: The Vela Pulsar.

And on Thursday (Oct. 5), scientists announced that data from the High Energy Stereoscopic System (HESS) observatory in Namibia indicates this cosmic marvel just became a little more marvelous. It would appear that Vela unleashed the highest-energy radiation ever seen coming from a pulsar.

Specifically, this object seems to have spit out gamma-ray photons — which are associated with wavelengths that carry the most energy of all electromagnetic spectrum waves — holding at least 20 teraelectronvolts (TeVs), or 20 trillion electronvolts. (1 electronvolt equals the amount of energy a single electron gains after being accelerated by 1 volt of electricity.)

To put that into context, Arache Djannati-Ataï, discovery team lead and scientist at the Astroparticle & Cosmology laboratory in France, says you'd need about 2,000,000 typical solar flare photons to make one 20 TeV photon. "As compared to visible light," Djannati-Ataï told Space.com, "one would need roughly 2x10^13 visible photons."

Though Vela is a pretty "normal" pulsar with rotations occurring 11 times per second, the researcher explains it's a key subject in astronomy because it's quite close to us — cosmically speaking, that is.

"Targeting it with our telescopes was almost mandatory!" 

Related: New kind of pulsar may explain how mysterious 'black widow' systems evolve

Typically, pulsars are expected to emit radiation with energies below tens of gigaelectronvolts (GeV), let alone fall into the extreme realm of TeVs. (1 gigaelectronvolt is equal to 1 billion electronvolts).

Even Vela, according to the team, originally exhibited a sort of cutoff when it comes to radiation emissions — in fact, even though some theoretical predictions had suggested Vela can emit in the TeV range, no one suspected the whopping 20 TeV figure the researchers managed to observe.

"We had searched for a pulsed emission from Vela at lower energies," Djannati-Ataï said, "But detecting photons reaching 20 TeV was really a surprise." The only other pulsar ever seen to have TeV-level emissions is the Crab Pulsar, located more than 6,000 light-years from Earth — yet even that one topped out at around 1 TeV.

And, finally, before we get into some implications of this high-energy sighting, there is one other intriguing finding to discuss about Vela. 

At risk of simplification, the team found that Vela's highly energetic photons corresponded to a previously unknown spectral component of pulsars. A pulsar's "spectrum" refers to a diagram that represents all the different light intensities and energies emitted by the object. (This is not exclusive to pulsars. Scientists can study lots of cosmic entity spectra so long as there's light involved).

So essentially, with Vela's spectrum, the team noticed a steeply rising pattern and clear break between the TeV emissions and lower-level emissions. What this means is the very energetic photons couldn't have been a continuation of lower energy photons such that the latter grew and grew (and grew) until they reached TeV status.

"This is in contrast to the Crab Pulsar," Djannati-Ataï said, where the energy spectrum is in continuation of its GeV emissions. 

What can we do with this information?

A NASA illustration of a pulsar, a rapidly rotating neutron star, that periodically points bursts of radiation at Earth. (Image credit: NASA's Goddard Space Flight Center)

As to what this might mean for astronomy in general, well, first and foremost, it tells us a ton about one of the most incredible items in our universe. 

"Within the zoo of cosmic objects, pulsars are fantastic," Djannati-Ataï said. "They are cosmic laboratories with incredible features that we cannot reach, by far, on Earth." 

Even the origin story of pulsars is quite an impressive one. They're the leftover, spinning corpses of stars that once died in a supernova explosion, are made almost completely of neutrons and they blast out beams of radiation that sometimes sweep across our solar system. It's actually those sweeps, which happen at regular time intervals, that allow scientists to map out the spectra of these bodies. 

Such extremity is also why scientists study the space around pulsars to test some major physical concepts, as Djannati-AtaΪ touches on by calling them "cosmic laboratories." Most notably, experts like to see whether Albert Einstein's theory of general relativity holds around pulsars because these objects are some of the most gravitationally intense things in the universe — and general relativity is a mind-bending explanation for gravity itself. To that end, as far as we know, it does. 

Further, Djannati-Ataï says these findings provide stringent constraints around our understanding of the source of pulsar radiation. Right now, scientists believe that source to be fast-moving electrons produced and accelerated in the pulsar's magnetosphere, which then travel toward the object's periphery. This model doesn't really explain the team's observations, however; other stuff needs to happen to produce emissions with energies as high as 20 TeV. 

And though the researchers have some ideas, they intend to fully solve that puzzle with future observations. For now, we can enjoy how these results have officially opened up a new path for scientists who work among the stars. 

As Djannati-Ataï puts it, "TeV pulsar astronomy is born!"

A study on these results was published Oct. 5 in the journal Nature Astronomy.

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Monisha Ravisetti
Astronomy Channel Editor

Monisha Ravisetti is Space.com's Astronomy Editor. She covers black holes, star explosions, gravitational waves, exoplanet discoveries and other enigmas hidden across the fabric of space and time. Previously, she was a science writer at CNET, and before that, reported for The Academic Times. Prior to becoming a writer, she was an immunology researcher at Weill Cornell Medical Center in New York. She graduated from New York University in 2018 with a B.A. in philosophy, physics and chemistry. She spends too much time playing online chess. Her favorite planet is Earth.