Black hole shoots plasma every which way

Astronomers have revealed the bizarre behaviour of a black hole known as V404 Cygni, located some 8000 light-years from Earth, describing it as “one of the most extraordinary black hole systems” ever observed.

In a study published in the journal Nature, a team led by James Miller-Jones, from the Curtin University node of the International Centre for Radio Astronomy Research (ICRAR), in Western Australia, reveals that the black hole is shooting out jets of high-speed plasma in several directions.

V404 Cygni is feeding on a nearby star, sucking gas away from it and forming a disc of material which circles the hole’s event horizon, gradually being sucked in.

That in itself is standard practice for black holes. Indeed, researchers using the Karl G Jansky Very Large Array (VLA) radio-astronomy observatory in New Mexico, US, recently succeeded in imaging such a disc for the very first time.

“What’s different in V404 Cygni is that we think the disk of material and the black hole are misaligned,” explains Miller-Jones. 

“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.”

The system’s weird behaviour first came to light in 1989, when astronomers detected a big outburst of jets and radiation. Checking archival images, the astronomers realised that something similar had happened in 1938 and 1956.

Interest thus piqued, when V404 Cygni let loose with an extraordinary burst of brightness over a two-week period in 2015, telescopes around the globe were turned towards it.

“Everybody jumped on the outburst with whatever telescopes they could throw at it,” says Miller-Jones. “So, we have this amazing observational coverage.”

Jets extending from black holes typically start at the poles. The ones emanating from V404 Cygni, in contrast, burst out from many different areas, and changed direction frequently – as often as every few hours.

The reason for the unusual behaviour, the researchers suggest, is due to the alignment of the hole’s 10 million kilometre-wide accretion disc, the innermost section of which was seen to be wobbling.

“The inner part of the accretion disk was precessing and effectively pulling the jets around with it,” Miller-Jones says.

“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.”