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Astronomers explore mystery of powerful black hole ‘Death Star’ style beams

Published: 30 October 2017
Artist’s impression of a relativistic jet shooting out from close to the black hole in the V404 Cygni binary system. Credit: G Pérez Díaz (IAC)

A team of scientists led by the University of Southampton has moved a step closer to understanding mysterious cosmic phenomena – known as relativistic jets – that shoot out from the vicinity of black holes.

The ultra-powerful jets, which have been likened to deadly rays fired from Star Wars super-weapon the Death Star, have been observed by measuring how quickly they ‘switch on’ and shine brightly once they are launched.

In a new study published today in Nature Astronomy, an international team of scientists led by Dr Poshak Gandhi show how they used precise multi-wavelength observations of a binary system called V404 Cygni to throw light on this hotly debated phenomenon.

Poshak, an Associate Professor in Southampton’s Department of Physics and Astronomy, says, “Scientists have been observing jets for decades, but are far from understanding how nature creates these mind-bogglingly vast and energetic structures.

“Now, for the first time, we have captured the time delay between the appearance of X-rays and the appearance of optical light in a stellar-mass black hole at the moment jet plasma is activated. This lays to rest the controversy regarding the origin of the optical flashes, and also gives us a critical distance over which jet plasma must have been strongly accelerated to speeds approaching that of light.”

The key measurement of this study can be compared in the Star Wars universe to measuring the distance between the surface of the Death Star, where multiple rays of light shoot out, and the point where they converge into a single bright beam.

“But the physics of black hole jets has nothing to do with lasers or the fictional Kyber crystals that power the Death Star,” Poshak adds. “Nature has found other ways to power jets. Gravity and magnetic fields play the key roles here, and this is the mechanism we are trying to unravel.”

Poshak and his collaborators captured the data in June 2015, when V404 Cygni was observed radiating one of the brightest ‘outbursts’ of light from a black hole ever seen – bright enough to be visible to small telescopes used by amateur astronomers, and energetic enough to tear apart an Earth-like planet if properly focused.

Using telescopes on Earth and in space observing at exactly the same time, they captured a 0.1-second delay between X-ray flares emitted from near the black hole, where the jet forms, and the appearance of visible light flashes, marking the moment when accelerated jet plasma begins to shine. This ‘blink of an eye’ delay was calculated to represent a maximum distance of 19,000 miles (30,000 km), impossible to resolve at the distance of V404 with any current telescope.

As well as Southampton, the research involved the universities of Sheffield, Oxford, Cambridge and Warwick, in the UK, as well as universities in Italy, Spain, France, USA, Canada, Netherlands, Switzerland, India, Germany and the United Arab Emirates.

See an animation which illustrates the cosmic phenomena.

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