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In 2015, the Cygni V404 black hole had attracted the attention of astronomers around the world when it suddenly lit up for two weeks. The explosion occurred when the black hole began to engulf the materials of a star that gravitates once every six days. When the material swirled in the black hole, it heated enough to shine brightly. Then, the black hole begins to film some of this material far into the space in the form of beams of bright jets. When astronomers looked closely at the jets, they realized that they were oscillating like a vertex.
Normally, when astronomers see jets spouting from a black hole, the features are oriented in one direction. But in this case, the rotation of the black hole is shifted relative to the disk of material swirling around it. And thanks to relativity, the black hole also drags the space-time around it, distorting the disk. This misalignment makes the jets draw a cone shape in space, creating a unique signature that astronomers are eager to understand and watch evolve in real time.
Black wobbly hole
Astronomers first noticed the V404 Cygni in a different explosion in 1989. Once the object was identified as a black hole some 8,000 light-years away from the object, they were able to watch older photographs of the same area and find that it had also exploded. 1938 and 1956.
ICRAR Cygni V404 black hole animation
The black hole itself is surrounded by a crepe-shaped debris cloud called accretion disk more than 6 million kilometers wide, consisting of a material that it is removing from the companion star nearby. Scientists would expect the material around the black hole to rotate in the same way as the black hole. But something – probably a kick from the supernova that first trained the V404 Cygni – pushed the black hole and disc out of alignment.
During its last blast in 2015, this misalignment was visible in the tilt of the jets, which wavered even under the eyes of astronomers, evolving in minutes to just a few hours. Researchers led by James Miller-Jones of the International Radioastronomy Research Center in Australia published their observations of the black hole and its flickering jets from April 29 to Nature.
"The inner part of the accretion disk was precession and was effectively pulling the jets with it," Miller-Jones said in a statement. "You can think of this as a flicker of a spinning top that slows in. Only in this case, this flicker is caused by Einstein's theory of general relativity."
Normally, astronomers see an object such as V404 Cygni with combined data hours. But because of the jittering of the jets, this gave the researchers a fuzzy picture. Instead, Miller-Jones and his team took several images of shorter shows to create a jerky movie of jet movements.
Sliding of space-time caused by the rotation of V404 Cygni is expected in situations like this, but having a clear picture of the situation at a time scale short enough to be observed is a treat for astronomers. It is likely that the V404 Cygni will explode again in the coming decades and that astronomers are surely waiting with their cameras.
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