A Black Hole Just Awakened from Its Slumber

Black holes are famous for their capacity to devour anything unlucky enough to fall into them—including light (and especially Matthew McConaugheys).

But that doesn't necessarily mean that black holes always appear as dark cosmic sinkholes in the skies, as evidenced by a recent eruption of high-energy light bursts from V404 Cygni, a tempestuous binary system comprised of one black hole and one star (any two objects in space that orbit each can be considered a binary system, though the term is typically used for star systems).

After 26 years of electromagnetic slumber, V404 Cygni, which is located 8,000 light years away in the constellation Cygnus, has finally reawakened and is emitting some extremely bright X-ray blasts.

Both the black hole and its companion star that comprise V404 Cygni are fairly petite as far as astronomical objects go (the hole is only 12 solar masses, and the star is a nudge smaller than the Sun). But don't let their relatively puny sizes fool you, because the interaction between the pair is packing a very pyrotechnic punch.

Essentially, the black hole's gravitational tug is constantly pulling off a steady stream of gas runoff from the star, and bending the star itself into an egg-like oval shape. The gas builds up along the black hole's accretion disk, which is a ring of material that forms outside a hole's event horizon.

Every so often, the amount of space junk that has collected around the disk reaches a tipping point, and the result is an explosive blast of gamma and X-ray radiation. V404 Cygni seems to run through this cycle about once every 30 years or so, and guess what? It's happening again right now.

On June 15, NASA's Swift satellite snagged the first evidence that this system, which has been dormant since 1989, was reawakening. This was the starting gun for a huge mobilization of telescopes and instruments that specialize in detecting energetic bursts to point their receivers toward Cygnus to capture this rare event.

"The behaviour 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," said Erik Kuulkers, who manages the INTErnational Gamma-Ray Astrophysics Laboratory (INTEGRAL) space observatory, in a statement released today.

"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," he added.

The fact that these two small objects can generate such spectacular fireworks is a testament to the strong forces at play on black hole accretion disks. In fact, when these kinds of interactions occur on an even larger scale—for example, with quasars—they can produce the most luminous light shows in the universe.

So while black holes have built up a name for themselves as the literal dark horses of the cosmos, V404 Cygni is the latest example of how these objects power some of its most radiant phenomena. And along those lines, astronomers like Kuulkers are just happy to be along for the ride.

"The community couldn't be more thrilled," he noted. "Many of us weren't yet professional astronomers back [in 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 said.