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The Event Horizon Telescope captured a jet of searing gas from a distant galaxy that bends sharply right at its base, and we’re looking straight down the beam, like into a spotlight.
In April 2021, a vast network of radio dishes, united as the EHT (EHT), trained its gaze on a tiny point in the constellation Virgo. That point is the active galactic nucleus of the distant galaxy 3C 279, from which a powerful jet (a stream of plasma) erupts. The jet is made of plasma — matter heated to billions of degrees and accelerated to near the speed of light, shining incredibly brightly. For the first time, EHT has revealed what happens at the very base of this beam, and the picture stunned researchers: the jet is not straight but bends sharply at a wide angle, like a garden hose kinked right at the nozzle. We are staring straight down it, like into a spotlight aimed directly at our eyes.
This bend has persisted for years: it was already noticed in 2011, 2017, and 2021, so it’s no fluke. When astronomers measured the speed of plasma blobs in the jet using Very Long Baseline Interferometry (a method that links telescopes across continents), they got an illusion: the blobs seemed to be flying ten times faster than light. But this is a geometric trick. If an object races at nearly the speed of light at a slight angle to our line of sight, the light from it reaches us in a way that makes the motion appear sped up. On top of that, when a source is moving toward us, its emission gets brighter, like an ambulance siren sounding higher pitched as it approaches. This effect was discovered by Christian Doppler, and it makes the beam even more conspicuous. In reality, the speed is still below the speed of light; it’s just geometry warping the picture. This tells us that the jet is aimed almost exactly at us — within an angle of less than a degree, like the width of a coin seen from a few kilometers away.
The plasma in the jet can reach a temperature of ten billion degrees. But because of the laws of relativity (thanks to Albert Einstein and Hendrik Lorentz), in the particles’ rest frame it falls below a critical threshold, and that lets us peer deep into the flow, not just see its surface.
What makes the jet bend? The prime suspects are the fierce magnetic fields near the supermassive black hole. As plasma erupts from the accretion disk (the swirling cloud of gas around the black hole), magnetic field lines can undergo magnetic reconnection (breaking and reconnecting in new ways), abruptly changing the flow’s direction. Another possible culprit is the interstellar medium (the tenuous gas between stars), which the jet slams into. Unraveling this mechanism will tell us how black holes at the centers of galaxies shoot out energy across millions of light-years. For now, our planet remains right in the beam of this cosmic spotlight: shift a little to the side, and the source would vanish.
3C 279 was one of the first distant galaxies with strong variability, discovered in 1971. Even back then, astronomers suspected that its beam was aimed straight at Earth. The Event Horizon Telescope confirmed this with stunning precision: the angle is less than a degree — about like spotting a coin from a few kilometers away.
In Stanisław Lem’s novel Fiasco, the characters encounter a civilization that sends signals in narrow beams. Stray a little to the side, and contact is lost. It’s the same with this cosmic spotlight: we only see it as long as we’re right in the beam.
