Om nom nom: Black hole dismembers and eats a large planet And burps up gamma rays that are visible from another galaxy.

Computer simulation of a black hole stripping material off a brown dwarf or large planet, shown at the lower right. The material flowing onto the black hole produces a burst of gamma rays and X-rays.

Black holes have a fearsome reputation that's only partly justified. The maw of a black hole is indeed a potentially destructive thing, but most matter—including gas stripped from nearby stars—is not destined to end inside the black hole. Instead, a lot of it ends orbiting the black hole, and the energy that's released by the material that is getting swallowed blasts a lot of material back out into space. So, black holes don't simply devour every object that comes near them.

All of this makes a new observation particularly interesting. Astronomers M. Nikołajuk and R. Walter caught a black hole in the act of destroying and consuming part of a large planet or small brown dwarf. This event involved a supermassive black hole located in a relatively nearby galaxy, and emitted a burst of intense X-ray light that fluctuated over a short time span, then faded. The flare and its aftermath behaved as expected if the black hole disrupted an object at least 14 times Jupiter's mass, then consumed about 10 percent of the gas that once was part of the object.

In 2011, astronomers using the INTEGRAL (INTErnational Gamma-Ray Astrophysics Laboratory) gamma ray telescope discovered a strong source of emissions coming from the galaxy NGC 4845. Follow-up observations using INTEGRAL along with other gamma- and X-ray telescopes confirmed the flare was located within the central region of the galaxy, where the supermassive black hole resides.

Typically, as matter falls onto a black hole at the center of a galaxy, it forms an accretion disk, a rotating region of material that heats to very high temperatures. The result is often strong emissions in gamma rays and radio light, with the output fluctuating only slightly.

However, the subsequent observations of NGC 4845 found the emissions fluctuated by a huge amount over a matter of days. After the light emission peaked, they faded over the course of a year, behavior very unusual for a supermassive black hole. The researchers suspected a one-time event, rather than the normal, steady diet of most black holes.

The authors used calculations of energy output and the measured variation of light emissions to work backward to what could have produced the burst. They found a relatively small amount of mass could do the trick, provided it hit the black hole fairly quickly. This mass would be the equivalent to about 10 percent of the mass of either a very large planet or small brown dwarf, anywhere between 14 and 30 times the mass of Jupiter.

(Brown dwarfs are star-like objects with insufficient mass to start hydrogen fusion in their cores. There is sufficient overlap between large planets and small brown dwarfs that it's hard to distinguish between them, but let's say the black hole ate a planet because that's more fun.)

The researchers compared this scenario to other possible explanations for the flare, including the possibility of a small star coming close to the black hole, or a brief window opening in the shroud of gas surrounding the black hole. They concluded the planet or brown dwarf was a more likely result, based on the specific behavior observed.

In the scenario proposed in the new paper, the super-Jupiter drifted close to the supermassive black hole in NGC 4845. The gravitational attraction on the near side of the planet was stronger than on the far side, pulling it out of shape. (This is known as the tidal force, and it is responsible for the twice-daily tides on Earth.) At some point, the internal force of gravity holding the planet together was insufficient to keep the black hole from ripping about 10 percent of the mass off in one burst.

This matter fell onto the black hole, creating a particularly bright but fluctuating accretion disk. It also made a corona-like cloud around the black hole, the first event of its kind ever observed. Some of the disrupted material eventually returned to the planet, while some was eventually swallowed by the black hole. As the planet moved away, there was a gradual fading of the light emissions, consistent with the data.

Such tidal disruptions are rare events, with perhaps one occurring in a million years' time for a given galaxy. However, there are a lot of rogue planets drifting around, unattached to any star, so the authors suggest that planet disruptions might be at least as common as stars being disrupted. With all the supermassive black holes in all the galaxies in the Universe, the chances of seeing another planet-munching black hole are pretty good, if we know what we're looking for.