Black holes got their name because they have such intense gravity that, once inside their event horizons, not even light can escape. Somewhat ironically, they're also some of the brightest objects in the Universe. That's entirely because of things that happen outside of the event horizon. There, the hole's intense gravity draws matter into a disk and raises it to very high energies. The disk emits lots of light on its own and sends out jets of high energy particles that emit even more as they interact with the surrounding interstellar material.

But this process has a limit—literally called the Eddington limit. At some point, the radiation emitted by the black hole starts driving off the surrounding matter, effectively cutting off its own food supply. You can view the Eddington limit as the point where matter intake is optimal; below it, the hole can swallow more than the environment's feeding it, while above, matter is being driven off before it can be eaten.

Now, thanks to new observations of a black hole in the Southern Pinwheel galaxy (Messier 83), researchers have found that the Eddington limit isn't an absolute cap on the amount of energy a black hole can emit out into its surroundings. Their observations suggest that this particular black hole sends out almost as much energy in the form of accelerated particles.

This isn't a completely unexpected result. We've known about the particle jets for a while, but to see how they compare to the Eddington limit, you have to actually be able to figure out what the Eddington limit is. That requires a detailed measurement of the mass of the black hole, which has been challenging given that there are significant uncertainties about the mass of the immense black holes that reside at the center of most galaxies.

In the nearby Universe, there are a number of areas where an intense X-ray source is surrounded by a large bubble of gas energized by a shock wave. These bubbles are almost certainly cleared out by particles shot out of the black hole. But again, we can't image the black holes well enough to determine their mass.

That's changed with the discovery of a microquasar in the spectacular Southern Pinwheel galaxy. A microquasar is like the light and jets that are emitted by the black holes at a galaxy's core, but instead it's produced by a stellar mass black hole.

A large suite of observations with several pieces of hardware put hard limits on the properties of this microquasar. The Chandra X-ray observatory identified a point source of photons within the object, which allowed them to estimate the black hole's mass (about 115 times the mass of the sun). Radio emissions were imaged to locate the shock front caused by energetic particles slamming into the interstellar gas. That was used to estimate the total amount of kinetic energy being emitted with these particles.

The net result is that the average kinetic power emitted by the black hole is 3 × 1040 ergs/second, which is 3 × 1033 Watts, more commonly referred to as "a lot." It's also greater than the Eddington limit of a black hole of this mass, which suggests there are times when, in light and kinetic energy combined, the black hole can emit more than double the Eddington limit.

The supermassive black holes at the center of galaxies are thought to shape the galaxies that host them by controlling how much gas is available for star formation. So the more energy they pump out into their environs, the more likely they are to drive the gas away from the galactic center and suppress star formation.

Science, 2014. DOI: 10.1126/science.1248759 (About DOIs).