Spinning black hole sprays light-speed plasma clouds into space

29 April 2019

Astronomers have discovered rapidly swinging jets coming from a black hole almost 8000 light-years from Earth.

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 high-speed clouds of plasma—potentially just minutes apart—shooting out of the black hole.

Animation of the precessing jets and accretion flow in V404 Cygni. The animation zooms in from the high-speed plasma clouds observed with our high angular resolution radio observations to show the binary system itself. Mass from the normal star spirals in towards the black hole via an accretion disk, whose inner regions are puffed up into a doughnut-shaped structure. The spinning black hole, which is misaligned with the binary orbit, pulls spacetime (the green gridlines) around with it, causing the puffed-up inner disk to precess like a spinning top, redirecting the jets as it does so. Credit: ICRAR

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 released a big outburst of jets and material.

Astronomers looking at archival photographic plates then found previous outbursts in observations from 1938 and 1956.

Associate Professor Miller-Jones said that when V404 Cygni experienced another very bright outburst in 2015, lasting for two weeks, telescopes around the world tuned in to study what was going on.
“Everybody jumped on the outburst with whatever telescopes they could throw at it,” he said.
“So we have this amazing observational coverage.”

When Associate Professor Miller-Jones and his team studied the black hole, they saw its jets behaving in a way never seen before. Where jets are usually thought to shoot straight out from the poles of black holes, these jets were shooting out in different directions at different times.

And they were changing direction very quickly—over no more than a couple of hours. Associate Professor Miller-Jones said the change in the movement of the jets was because of the accretion disk—the rotating disk of matter around a black hole.

He said V404 Cygni’s accretion disk is 10 million kilometres wide, and the inner few thousand kilometres was puffed up and wobbling during the bright outburst.
“The inner part of the accretion disk was precessing and effectively pulling the jets around with it,” Associate Professor Miller-Jones said.
“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.”

High-speed plasma clouds ejected from V404 Cygni over a four-hour period on 22nd June, 2015. This movie is made directly from our high-resolution radio images taken with the National Science Foundation's Very Long Baseline Array. It shows clouds of plasma in the precessing jets moving away from the black hole in different directions. The scale of the images is approximately the size of our Solar System, and time is shown by the clock in the bottom right-hand corner. Credit: ICRAR and the University of Alberta

The research used observations from the Very Long Baseline Array, a continent-sized radio telescope made up of 10 dishes across the United States, from the Virgin Islands in the Caribbean to Hawaii.

Co-author Professor Rob Fender, from our sub-department of Astrophysics said:

“Over 25 years we’ve been refining our understanding of how jets are launched from these star-sized black holes, but we’ve never seen anything like this before.”
“We have built up a picture of how the regions of space very close to a black hole determine the properties of these incredible jets we see in the radio images, and this is a very important new piece in the puzzle.”

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