Astronomers witness black hole dragging spacetime

Books Wednesday 01/May/2019 14:10 PM
By: Times News Service
Astronomers witness black hole dragging spacetime

San Diego: Astronomers from around the world witnessed a black hole 8000 light-years pumping "rapidly swinging jets" into the surrounding universe in a way that has never been seen before.

Known as V404 Cygni, researchers said the black hole appears to be shooting out powerful beams of plasma at a rate of speed so fast that it's "dragging spacetime". The findings were recently published in the journal Nature.

Lead author of the findings, Associate Professor James Miller-Jones from Australia's Curtin University node of the International Centre for Radio Astronomy Research (ICRAR) said, "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."

According to ICRAR, V404 Cygni was first identified as a black hole in 1989 when it released a big outburst of jets and radiation. Astronomers looking at archival photographic plates have found previous outbursts in observations from 1938 and 1956.

Associate Professor Miller-Jones stated 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 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. They were changing direction very quickly, over no more than a couple of hours.

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. According to the Associate Professor, 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. 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."

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

Co-author Alex Tetarenko from the University of Alberta, who is currently working as an East Asian Observatory Fellow in Hawaii stated because the jets were changing direction, scientists "had to use a very different approach to most radio observations."

"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," she explained. "It was like trying to take a picture of a waterfall with a one-second shutter speed."

"Instead, the researchers produced 103 individual images, each about 70 seconds long, and joined 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."

Study co-author Dr Gemma Anderson, who is also based at ICRAR’s Curtin University node, said the wobble of the inner accretion disk could happen in other extreme events in the Universe too.

“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,” Dr Anderson said.

“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.”