A sleeping cosmic giant has awakened after 26 years, say astronomers who've been watching the black hole greedily consuming material from its companion star.
The black hole and its orbiting stellar neighbor, around 8,000 light years from Earth, make up a system known as V404 Cygni.
A European Space Agency satellite called Integral has been detecting an incredible outburst of high-energy light, and the agency reports V404 Cygni hasn't shone so brightly since 1989.
It experienced similar brightening in 1938 and 1956, and scientists say the newest outburst is yielding clues to what's behind the periodic peaks of energy activity.
In a binary system consisting of a black hole with a companion star, material is pulled from the nearby star toward the black hole and creates a disk around it that is heated to extreme temperatures and begins shining at optical, X-ray and ultraviolet wavelengths just before it spirals down and disappears in the black hole, astronomers explain.
In the case of V404 Cygni, they theorize the periodic outbursts occur when material from the orbiting star approaching the black hole reaches a critical mass in the disk, causing a change in the rate at which the black hole begins to absorb it.
Such a change in the rate could be accompanied be a brilliant glow from the star's material as it is consumed, they say.
"The behavior of this source is extraordinary at the moment, with repeated bright flashes of light on time scales shorter than an hour, something rarely seen in other black hole systems," says Erik Kuulkers, ESA Integral project scientist.
"In these moments, it becomes the brightest object in the X-ray sky — up to 50 times brighter than the Crab Nebula, normally one of the brightest sources in the high-energy sky."
Following the first detections by a NASA satellite, astronomers around the world began conducting observations using both ground-based telescopes and orbiting astronomical observatories to watch V404 Cygni at a number of different wavelengths on the electromagnetic spectrum.
"Now that this extreme object has woken up again, we are all eager to learn more about the engine that powers the outburst we are observing," says Carlo Ferrigno at the Integral Science Data Center at the University of Geneva.
Many astronomers expressed excitement at the prospect of seeing a black hole in such violent action after a long slumber, with Kuulkers noting "many of us weren't yet professional astronomers back then (1989), and the instruments and facilities available at the time can't compare with the fleet of space telescopes and the vast network of ground-based observatories we can use today.
"It is definitely a 'once in a professional lifetime' opportunity," he adds.
