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Spinning black hole shots light-speed plasma jets into space

An artist's impression of the inner parts of the accretion disk in V404 Cygni. The black hole rotates about a different axis to the binary orbit. As the spinning black hole drags spacetime around with it, the puffed-up inner accretion disk wobbles around like a spinning top. Credit: ICRAR
Einstein's theory of general relativity explains the black hole’s behavior
by TR Pakistan

Astronomers have discovered jets of fast-moving material shooting out of V404 Cygni, a black hole nearly 8,000 light-years from Earth. The results of this research was published on April 29, 2019 in the scientific journal Nature.

The jets are shooting out of the black hole in different directions and rotating so fast that their change in direction can be seen in periods as short as minutes.

“We’ve never seen this effect happening on such short timescales,” said lead author James Miller-Jones, of the Curtin University node of the International Center for Radio Astronomy Research (ICRAR).

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V404 Cygni, a black hole nine times more massive than the Sun, is drawing in material from a companion star. As the material streams toward the black hole, it forms a rotating disk, called an accretion disk, surrounding the black hole. In such systems, the disk becomes denser and hotter with decreasing distance from the black hole. Either the innermost portion of the disk or the black hole itself launches jets of material outward away from the disk. However, these jets are usually thought to shoot straight out from the poles of the black hole.

“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,” said Miller-Jones in a press release.

“This is the only mechanism we can think of that can explain the rapid precession we see in V404 Cygni,” he added. 

While V404 Cygni’s accretion disk is about 10 million kilometers wide, Miller-Jones pointed out that only the inner few thousand kilometers is warped. 

Such a rapid wobble, called precession, as that in V404 Cygni has not been seen before in other such systems. To explain that phenomenon, the astronomers said, requires using Einstein’s general theory of relativity which says that massive objects like black holes distort space and time. When such a large object is spinning, its powerful gravitational influence pulls space and time around with it, an effect which is called frame-dragging.

The jets’ rapid direction changes meant that astronomers had to change their observation strategy. Normally, astronomers will produce a single image using data collected over as much as several hours, like a long time exposure.

“These jets were changing so fast that in a four-hour image we saw just a blur,” said co-author Alex Tetarenko, a recent Ph.D graduate from the University of Alberta and currently an East Asian Observatory Fellow working in Hawaii.

To capture the rapid motion, the researchers made 103 individual images, each about 70 seconds long, then combined them to make a movie.

The result, according to Greg Sivakoff, of the University of Alberta, indicates that similar behavior could be found in other objects.

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“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?’”

V404 Cygni first came to astronomers’ attention in 1938, when it experienced an outburst, and got its designation as a “variable star.” Another outburst was observed in 1989, and follow-up studies revealed a previously-unnoticed outburst in 1956.

A new outburst which lasted two weeks was detected by NASA’s Swift satellite in 2015, triggering a worldwide observing effort. The observations from the Very Long Baseline Array (VLBA), a continent-sized radio telescope made up of 10 dishes across the United States, from the Virgin Islands in the Caribbean to Hawaii, began on June 17, 2015, and continued through July 11 of that year.

Observations from VLBA contributed to this research.

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