Astronomers discover rapidly-changing jet from black hole

    International team of scientists, including UAlberta astrophysicists, observe never-before-seen behaviour of a black hole.

    By Andrew Lyle on April 29, 2019

    An animation of the precessing jets and accretion flow in V404 Cygni narrated by associate professor James Miller-Jones of Curtin University and ICRAR. Zooming in from the high-speed plasma clouds observed with our radio telescope, we see the binary system itself. Mass from the star spirals in towards the black hole via an accretion disk, whose inner regions are puffed up by intense radiation. The spinning black hole pulls spacetime (the green gridlines) around with it, causing the inner disk to precess like a spinning top, redirecting the jets as it does so. Credit: ICRAR

    An international team of astronomers, including researchers at UAlberta, have discovered rapidly-swinging jets emitted from a black hole, a behaviour never seen before.

    The results show that jets from the black hole V404 Cygni, almost 8,000 light-years from Earth, wobble around on a much faster time scale than scientists have seen to-date—changing their orientation in a matter of hours.

    “In cases like this where we have a black hole and a nearby star, the gravity of the black hole pulls gas from the star into a disc which collapses inward,” said Gregory Sivakoff, University of Alberta astrophysicist and professor in the Department of Physics.“And when it ‘feeds’ in this way, the black hole can emit jets of material.”

    Researchers have traditionally thought that those jets are emitted from the black hole in similar directions—but when they took a closer look at Cygni, they found something unexpected.

    “What’s different in V404 Cygni is that we think the disk of material and the black hole are misaligned,” said lead author James Miller-Jones, associate professor from the Curtin University node of the International Centre for Radio Astronomy Research. “This appears to be causing the inner part of the disk to wobble like a spinning top and fire jets out in different directions as it changes orientation.”

    “Like a picture of a waterfall with a one-second shutter speed”

    Study co-author Alex Tetarenko—PhD graduate from UAlberta and currently a fellow at the East Asian Observatory in Hawaii—elaborated that the speed the jets were changing direction meant scientists had to use a very different approach to most radio observations.

    “Typically, radio telescopes produce a single image from several hours of observation,” she said. “But these jets were changing so fast that in a four-hour image we just saw a blur. It was like trying to take a picture of a waterfall with a one-second shutter speed.”

    To solve this challenge, the researchers took a series of 103 images capturing about 70 seconds each. Miller-Jones and Tetarenko then led the efforts to combine those images into a continuous video—a difficult task, as each image required its own careful analysis, but the result has been well worth the effort, illustrating this unique and unusual black hole behaviour.

    “We were gobsmacked by what we saw in this system—it was completely unexpected,” said Sivakoff. “Finding this astronomical first has deepened our understanding of how black holes and galaxy formation can work. It tells us a little more about that big question: ‘how did we get here?’”