Astronomers Can’t Pinpoint the Source of the Most Powerful Source of Radiation Ever Observed

Researchers just spotted the most energetic radiation in the Universe, and they’re coming from a pulsar that seemingly shouldn’t be able to make them.

A thousand light years away, a pulsar called Vela flashes Earth with bright bursts of energy 11 times every second: radio waves, visible light, x-rays, and gamma rays.

Astrophysicist Arache Djannati-Atai and his colleagues at the Astroparticle and Cosmology Laboratory in France used the High Energy Stereoscopic System telescope in Namibia and found that some of those gamma rays are far more energetic than anything astronomers have seen before. And right now, they have no explanation for it.

Djannati-Atai and his colleagues published their work in the journal Nature Astronomy.

The Strange Light of a Dead Star

The pulsar Vela has a reputation as one of the brightest pulsars in the sky in several wavelengths, from radio to gamma rays. A pulsar is the burned core of a dead star, spinning wildly on its axis and surrounded by an intensely powerful magnetic field; beams of radiation shine from its poles, and as the pulsar spins, those beams sweep through space like lighthouse beams. From our point of view here on Earth, then, the pulsar seems to flash or pulse (hence the name).

Until recently, astronomers thought that the most energetic gamma rays coming from Vela were a few billion electron volts strong. But using a telescope designed specifically to search for very energetic, short-wavelength gamma rays, Djannati-Atai and his colleagues just discovered that Vela is somehow pumping out gamma rays that carry 20 trillion electron volts of energy.

That makes Vela the source of the most energetic radiation in the universe (that we know of).

This illustration shows what Vela might look like if our eyes could see all the wavelengths of energy it radiates.


Here’s a quick recap of the physics: Light, or any kind of radiation, is made of photons. The more photons you see, the brighter the source looks. But each individual photon also carries a certain amount of energy. Photons with more energy have shorter wavelengths. This makes sense if you picture an energetic photon excitedly bouncing up and down while a low-energy photon moves in slow, lazy ripples.

Gamma rays are already the most energetic type of radiation that we know of, but some gamma rays pack more energy than others. The previous record-holder was a gamma ray burst released by a massive star collapsing into a black hole, which astronomers spotted late last year; each photon carried 18 trillion electron volts of energy. That was pretty impressive; gamma ray bursts are extremely energetic, but they still usually “only” pack a few billion electron volts, so last year’s record-setter was at least a thousand times more powerful than usual.

And now there’s Vela, with gamma rays blasting out of its poles with 20 trillion electron volts of energy (and flashing us every 11 seconds as the pulsar twirls frantically on its axis). Astrophysicists studying the energetic gamma ray jet still don’t fully understand why this is occurring.

Magnetic Field Mystery

A pulsar’s powerful magnetic field is basically an enormous, intensely powerful version of the particle accelerators at SLAC or the Large Hadron Collider. Electrons get pulled along the magnetic field’s lines, reaching incredible speeds before getting flung out into space in jets at the north and south poles — and in the process, those speeding electrons release huge amounts of energy, creating the pulsar’s spinning searchlight beams.

The problem is that based on everything physicists know about its magnetic field, how fast it spins, and the speed and strength of its particle jets, Vela shouldn’t be able to get electrons moving fast enough to release 20 trillion electron volts of energy. To put it in mechanical terms, the particle accelerator just isn’t long enough.

That suggests something else, aside from the particle jets, should be producing the super-energetic gamma rays. Djannati-Atai and his colleagues say it could be a process happening in the magnetic field somewhere beyond the end of the jets, or something related to the pulsar’s powerful winds, although neither of those scenarios completely explains what they’re seeing. Nothing they’ve thought of so far could produce radiation with quite so much energy. Further, the energetic gamma rays still seem to be related to the jets because they flash with the same 11-times-per-second period as the other radiation coming from Vela.

There’s only one way to solve a cosmic puzzle like this one: Do more science.

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