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Sci-Tech

Slumbering black hole in Milky Way roars back to life

A black hole that hasn't been heard of since 1989 has suddenly become active again and is now the brightest object in the X-ray sky.

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An artist's impression of a black hole. The jets at the top and bottom consist of material that escapes the black hole's massive gravity field. NASA/ESA/JPL-Caltech/STScI/R. Hurt (SSC)

About 8,000 light-years from Earth, a black hole and a star dance around each other in the constellation Cygnus, the swan. Black holes emit energy as matter heats up before being devoured in the depths of super-gravity; since 1989, however, the black hole in that system -- known as V404 Cygni -- has been relatively quiet. That is, until now.

The European Space Agency (ESA) reported June 26 that its Integral satellite started picking up "an exceptional outburst of high-energy light" from the black hole. That's after activity from V404 Cygni had been spotted by NASA's Swift satellite, and an X-ray flare was found by the MAXI unit (Monitor of All-sky X-ray Image), which is part of the Japanese module on the International Space Station.

The ESA put its Integral gamma-ray observatory to the task of observing V404 Cygni on June 17 and have confirmed that the black hole is indeed active again. In fact, it's incredibly active.

"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," comments astronomer 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."

NASA has also observed a massive black hole at the center of the Sculptor galaxy go to sleep, as reported in June 2013. While it's typical for a black hole to go dormant after it's chewed up all the matter around it, it's a bit rare for one to stop being active when there is still matter nearby -- such as the star in V404 Cygni.

While the reason these massive matter-munchers wake and go dormant is still not fully understood, there are now more astronomical tools than ever with which to watch the process.

"The community couldn't be more thrilled: many of us weren't yet professional astronomers back then, 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," said Kuulkers. "It is definitely a 'once in a professional lifetime' opportunity."