Mocanu and Grumiller have now taken this idea to a new level. Should many of these axions accumulate around the black hole, a busy "boson-cloud" may form - like a huge swarm of bees around their hive. Although individual axions carry close to zero mass, through sheer numbers, their collective mass could carry some serious heft. (Indeed, the collective mass of axions throughout the Universe are thought to carry at least some of the mass locked in cold dark matter.)
OK, black holes might be surrounded by a huge cloud of axions, so what?
HOWSTUFFWORKS: How Black Holes Work
"Just like a loose pile of sand, which can suddenly slide, triggered by one single additional grain of sand, this boson cloud can suddenly collapse," Grumiller said in a press release.
As the boson cloud will likely be carrying some significant mass, a sudden collapse - known as a "bose-nova" - would generate a huge amount of energy, rippling the fabric of space-time. These ripples are known as gravitational waves and we have detectors that may be able to observe them by 2016.