A black hole in a binary system almost 8000 light-years from earth has been discovered to show rapidly swinging jets in new research involving the University of Amsterdam’s Professor Sera Markoff and Dr. Thomas Russell. Published today in the journal Nature, the research shows jets from V404 Cygni’s black hole behaving in a way never seen before on such short timescales. The jets appear to be rapidly rotating with a tilt, while ejecting blobs of plasma at near light-speed, like a cosmic lawn sprinkler.
Lead author Associate Professor James Miller-Jones, from the Curtin University node of the International Centre for Radio Astronomy Research (ICRAR), said black holes are some of the most extreme objects in the Universe.
‘This is one of the most extraordinary black hole systems I’ve ever come across,’ Associate Professor Miller-Jones said. ‘Like many black holes, it’s feeding on a nearby star, pulling gas away from the star and forming a disk of material that encircles the black hole and spirals towards it under gravity. What’s different in V404 Cygni is that we think the disk of material and the black hole are misaligned. 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.’
V404 Cygni was first identified as a black hole in 1989 when it emerged from quiescence with a huge outburst of activity, also including jets, before fading away for almost 30 years. Astronomers looking at archival photographic plates then found previous outbursts in observations from 1938 and 1956. When V404 Cygni experienced its next very bright outburst in 2015, which lasted two weeks, telescopes around the world jumped in to monitor the source during its outburst
When Miller-Jones and an international team, including Markoff and Russell, studied the black hole, they saw its jets behaving in a way never seen before. Where jets are usually modelled as shooting straight out along the poles of black holes, these jets were shooting out in different directions over time. And they changed direction very quickly—in less than a couple of hours.
The oscillating jet direction appears to be caused by the accretion disk—the rotating disk of infalling matter around a black hole. ‘The inner part of the accretion disk was precessing and effectively pulling the jets around with it,’ Miller-Jones said.
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Because of the speed the jets were changing so rapidly, the scientists had to use a very different approach compared to most radio observations.
'Typically, radio telescopes produce a single image averaged over several hours of observation, 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 long shutter speed.', says Co-author Dr. Alex Tetarenko—a recent PhD graduate from the University of Alberta and currently an East Asian Observatory Fellow working in Hawaii.
Instead, the researchers produced 103 individual images, each about 70 seconds long, and joined them together into a movie.
'It was only by creating such a movie, that we were able to see the individual blobs shooting out in different directions over a very short time period', Russell said.
The Anton Pannekoek Institute’s Professor Markoff helped with the interpretation of this source’s odd behaviour. 'At our institute we have begun to model such systems numerically, using a new code written by PhD student Matthew Liska. In a recent paper led by Liska and MSc student Casper Hesp, we could produce exactly this type of jet wobbling by starting the system off with a misalignment between accretion disk and black hole spin.'
"A rapidly-changing jet orientation in the stellar-mass black-hole system V404 Cygni". by: James C.A. Miller-Jones et al. In: Nature, april 30, 2019. https://www.nature.com/articles/s41586-019-1152-0