Apr 30 2019
Rapidly swinging jets, shooting out from a black hole nearly 8000 light-years from planet Earth, have now been discovered by astronomers.
Artist’s impression of V404 Cygni seen close up. The binary star system consists of a normal star in orbit with a black hole. Material from the star falls towards the black hole and spirals inwards in an accretion disk, with powerful jets being launched from the inner regions close to the black hole. (Image credit: ICRAR)
The study, which was recently reported in the journal Nature, demonstrates that jets coming from V404 Cygni’s black hole are acting in an extraordinary manner, which was never observed before on such short timescales.
It appears that the jets are quickly spinning with high-speed clouds of plasma—perhaps just minutes apart—coming out from the V404 Cygni’s black hole in various directions.
According to James Miller-Jones, lead author and Associate Professor from the Curtin University node of the International Centre for Radio Astronomy Research (ICRAR), the most extreme objects in the Universe are believed to be black holes.
This is one of the most extraordinary black hole systems I’ve ever come across. 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.
James Miller-Jones, Study Lead Author and Associate Professor, Curtin University, ICRAR.
In 1989, V404 Cygni was initially detected as a black hole when it emitted a huge outburst of radiation and jets. Astronomers examining archival photographic plates subsequently discovered earlier outbursts in observations between 1938 and 1956.
Miller-Jones informed that in 2015, V404 Cygni experienced another extremely bright outburst that lasted for a couple of weeks. Following this incident, telescopes across the globe tuned in to study what exactly was occurring.
“Everybody jumped on the outburst with whatever telescopes they could throw at it. So we have this amazing observational coverage.” Miller-Jones said.
When Miller-Jones, along with his group, examined the black hole, he found that its jets were behaving in an unusual manner, which was never encountered before.
Jets are often believed to directly come out from the poles of black holes, but these jets were coming out at different times in different directions, Moreover, the jets were changing direction extremely rapidly—over no more than two hours.
According to Miller-Jones, the accretion disk was responsible for the change in the jets’ movement. This accretion disk is the matter’s rotating disk around a black hole.
He further added that the accretion disk of the V404 Cygni is 10 million kilometers wide, and at the time of the bright outburst, the inner few thousand kilometers were puffed up and shaking.
The inner part of the accretion disk was precessing and effectively pulling the jets around with it. You can think of it like the wobble of a spinning top as it slows down—only in this case, the wobble is caused by Einstein’s theory of general relativity.
James Miller-Jones, Study Lead Author and Associate Professor, Curtin University, ICRAR.
The study made use of observations from the Very Long Baseline Array—a radio telescope that is the size of a continent and contains 10 dishes throughout the U.S., starting from the Virgin Islands located in the Caribbean to Hawaii.
According to Alex Tetarenko, co-author of the study and a fresh PhD graduate from the University of Alberta, the rate at which the jets were changing direction meant that an entirely different method has to be used by the researchers for a majority of radio observations. Tetarenko is now an East Asian Observatory Fellow working in Hawaii.
Typically, radio telescopes produce a single image from 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 one-second shutter speed.
Alex Tetarenko, Study Co-Author and Astrophysics Postdoctoral Fellow, East Asian Observatory.
The scientists instead created 103 separate images, with each being approximately 70 seconds long, and then connected them together into a movie.
“It was only by doing this that we were able to see these changes over a very short time period,” stated Dr Tetarenko.
According to Dr Gemma Anderson, study co-author and also based at ICRAR’s Curtin University node, the vibration of the inner accretion disk may also occur in other extreme events in the Universe.
Anytime you get a misalignment between the spin of a black hole and the material falling in, you would expect to see this when a black hole starts feeding very rapidly. That could include a whole bunch of other bright, explosive events in the Universe, such as supermassive black holes feeding very quickly or tidal disruption events, when a black hole shreds a star.
Dr Gemma Anderson, Study Co-Author, Curtin University, ICRAR
Narrated V404 Cygni Black Hole Animation
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 space time (the green gridlines) around with it, causing the inner disk to precess like a spinning top, redirecting the jets as it does so. (Video credit: ICRAR)