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An illustration shows how a gas cloud could break apart.

A simulation shows how a gas cloud approaching our galaxy's supermassive black hole may break apart.

Illustration courtesy Marc Schartmann, MPE/ESO

Jason Major

for National Geographic News

Published December 14, 2011

For the first time, a cloud of cool gas has been spotted approaching the supermassive black hole that lies at the center of our Milky Way galaxy—and astronomers are hoping they'll soon get to watch the monster feed.

Called Sagittarius A*—or Sgr A*, pronounced "A star"—the black hole is estimated to be about four million times as massive as our sun. All that mass is packed into a space about as wide as the distance between Earth and the sun, making the object so dense not even light can escape its gravity.

Although the black hole itself is invisible, astronomers can see the effects of its powerful gravity on nearby stars, some of which orbit Sgr A* at speeds of more than 600 miles (965 kilometers) a second.

In addition, when a black hole eats, it makes a mess, which is exactly what astronomers hope to witness.

Due to its intense gravitational pull, the invisible giant is believed to have gained mass by shredding and eating stars, nebulae, and even whole solar systems that ventured too close.

This has formed what's called an accretion disk—an orbiting disk of debris that's constantly falling into the black hole.

(See "Planets Being Pulverized Near Giant Black Holes?")

Astronomers have therefore been able to "see" our galaxy's supermassive black hole by looking at the steady stream of radiation created as superheated matter from the rapidly spinning disk falls in.

But the glow from Sgr A* is relatively dim compared with that from other galactic black holes that are more actively feeding, and the activity immediately surrounding the object is still poorly understood.

First Look at a Black Hole's "Table Manners"

Now, using the European Southern Observatory's Very Large Telescope (VLT) in Chile, an international team of scientists has found a cloud of charged gas that's about three times as massive as Earth accelerating toward the black hole's maw.

In fact, the cloud has already begun to break up due to the black hole's gravitational forces.

Models of how Sgr A* might affect the cloud "seem to be consistent with [the team's] observation of a progressive elongation of the blob, and perhaps with a gaseous tail following the blob in its orbit," Mark Morris, an astrophysicist at the University of California, Los Angeles, wrote in an accompanying commentary.

The team thinks the cloud will reach the event horizon—a black hole's point of no return—some time in 2013, creating a bright radiation flare that will shed new light on the black hole's feeding behavior.

(Related: "Mysterious Structures Balloon From Milky Way's Core.")

"This is really the very first time we will see how a black hole feeds. It's very exciting," said study co-author Stefan Gillessen, of the Max Planck Institute for Extraterrestrial Physics in Germany.

What's more, the black hole's "meal" should last for about ten years, he said, giving astronomers ample time to study what happens in the surrounding region.

Now that the cloud has been spotted, astronomers with the VLT's NACO and SINFONI programs will be watching closely to see how the event unfolds.

And according to UCLA's Morris, "many telescopes are likely to be watching."

The newfound black hole "snack" is described in this week's issue of the journal Nature.

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