EVENT HORIZON TELESCOPE FINDS BENT JET NEAR BLACK HOLE

Observations from the worldwide network of radio telescopes show the fire hose of plasma shooting from a distant galaxy does something strange near its source.

3C 279 is a paragon of quasars. This brilliant beacon is a black hole–powered glare at the center of a distant galaxy in Virgo, complete with a jet shooting right at us from the black hole. Astronomers call such down-the-barrel quasars blazars, and they’re the brightest quasars of the bunch.

Being the blazar archetype, 3C 279 has often been a target for observations. Astronomers are familiar with its flickering and epically long jet, which stretches thousands of light-years long. But Event Horizon Telescope scientists have discovered that, deep in the quasar’s heart, there’s something weird going on.

The EHT team used 3C 279 as a calibration source for its 2017 campaign to image the shadow of a black hole. The researchers observed the blazar on four separate days over a week, using eight radio telescopes at six stations spread across the world, from Antarctica to Arizona. By combining these antennas’ data together with a technique called very long baseline interferometry, astronomers were able to build images akin to those they would see if they had a radio telescope the size of Earth.

The resulting images are our most detailed look deep into the blazar’s core, coming less than half a light-year from the black hole itself. We’re converging on the jet’s origin. And here’s where the team found something strange: The jet appears to change direction.

This sequence of zooms shows what the jet shooting from 3C 279 looks like at different scales. Each scale comes from a different set of radio telescopes working at a particular wavelength: 7 mm (Very Long Baseline Array), 3 mm (Global Millimeter VLBI Array), and 1.3 mm (Event Horizon Telescope). The EHT image shows two components to the jet: one that points the same direction as the jet does farther out (bottom), and another that mysteriously points at right angles to the rest of the jet.
J.-Y. Kim (MPIfR), Boston University Blazar program, and the EHT Collaboration

One section of the jet points down in the image, the same direction as the jet does farther out. But the other one — the one closer to the black hole — is perpendicular to it.

Now I admit, the image above looks like an out-of-focus shot of two blobs. It’s the motions within the blobs that are fascinating. Each blob consists of at least three compact, bright regions, all moving with respect to each other. As you’d expect, the regions in the lower blob all travel in the same direction, aligned with the jet’s motion farther away — it’s a dependable outward flow.

But the regions in the blob at right angles don’t do any such thing. That part of the jet seems to be bent, as though the plasma stream contorts as it tries to escape from the black hole’s neighborhood.

This diagram shows the motions (red arrows) of six bright components in 3C 279's jet, measured with respect to one of the the six (C0-0, top right). The perpendicular jet feature is C0; the downward jet feature is C1. All of C1's components are moving the same direction. Choosing different points to use as the frame of reference doesn't fix the discrepancy. 
J.-Y. Kim et al. / Astronomy & Astrophysics 2020

Astronomers have seen bent jets emanating from other quasars. They’ve even seen signs of this same twisting in 3C 279 in previous observations, albeit not with this resolution. But finding such a dramatic turn so close to the black hole still surprised them. “This is like finding a very different shape by opening the smallest Matryoshka doll,” analysis leader Jae-Young Kim (Max Planck Institute for Radio Astronomy, Germany) said in a press release.

Various causes could explain the bend. Perhaps the black hole drags spacetime around itself as it spins and twists the base of the jet. Perhaps the jet rotates internally, which could create the same signal. Perhaps large-scale reconfigurations of the surrounding magnetic field create a knotty structure that isn’t as bent as it appears. Whatever it is, it’s intriguing.