Black hole awakes with renewed activity

V404 Cygni has renewed activity with its highest burst of high-energy light since 1989.

Artist's impression of a black hole feasting on material from its companion star.
Credit: ESA/ATG medialab

Astronomers have spotted a burst of high-energy light emanating from a black hole that has awoken and begun devouring material from its companion star.

V404 Cygni is located in the Milky Way almost 8,000 lightyears away in Cygnus. It is a binary system in which stellar material flows from the star towards its black hole and gathers in a disc. This then heats up and shines at optical, ultraviolet and X-ray wavelengths before it is sucked into the black hole.

On 15 June, V404 began its first period of high-energy activity since 1989, with a burst of gamma rays and high luminosity.

Evidence of the renewed activity was detected by the Burst Alert Telescope on NASA’s Swift satellite, initially as a gamma rays, then followed by observations using its X-ray telescope. Soon after, MAXI (Monitor of All-sky X-ray Image), part of the Japanese Experiment Module on the International Space Station, observed an X-ray flare from the same area.

A worldwide campaign was then launched by ground-based telescopes and space-based observatories to monitor V404 Cygni at different wavelengths across the electromagnetic spectrum. This included ESA’s Integral gamma ray observatory, which began observing on 17 June.

The black hole system last underwent a period of high-energy activity in 1989, when it was detected by Japanese X-ray satellite Ginga and instruments onboard the Mir space station.

It is thought that these peaks and troughs of activity occur because material builds up in the disk surrounding the black hole until it reaches a tipping point. This then precipitates a massive change in the rate at which the black hole devours surrounding material.

“The behavior of this source is extraordinary at the moment, with repeated bright flashes of light on timescales shorter than an hour, something rarely seen in other black hole systems,” says Erik Kuulkers, Integral project scientist at ESA.

“In these moments, it becomes the brightest object in the X-ray sky, up to fifty times brighter than the Crab Nebula, normally one of the brightest sources in the high-energy sky.”

“As coordinators of Integral operations, Enrico Bozzo and I received a text message at 1.30am on 18 June from our burst alert system, which is designed to detect gamma-ray bursts in the Integral data,” says Carlo Ferrigno from the Integral Science Data Center at the University of Geneva, Switzerland. “In this case, it turned out to be ‘only’ an exceptional flare since Integral was observing this incredible black hole: definitely a good reason to be woken up in the middle of the night!”

“The observations will soon be made available publicly, so that astronomers across the world can exploit them to learn more about this unique object,” says Peter Kretschmar, ESA Integral mission manager. “It will also be possible to use Integral data to try and detect polarisation of the X-ray and gamma ray emission, which could reveal more details about the geometry of the black hole accretion process. This is definitely material for the astrophysics textbooks for the coming years.”


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