Nature loves music
Uttley and McHardy are not the first scientists to find music, or so-called "flicker noise," in Nature's inaudible rhythms.
Similar patterns have been observed in everything from heartbeats to climate change. Other astronomers have detected flicker noise in X-ray outputs and in interplanetary magnetic fields.
Some scientists say music is ubiquitous in Nature (Earth itself
) and shows up in the arrangements of the planets, in seascapes, and even in our brainwaves. A few researchers have gone so far as to suggest, without any observational studies done of in-shower singing, that humans are born musical.
And in the 1970s, researchers found flicker noise in jazz, classical and other forms of manufactured music.
Uttley said the music of a black hole could be called improv. Pressed for some comparison to a specific artist or style, he said the late Greek composer Iannis Xenakis used flicker noise to randomly generate pieces called stochastic music. "You could use the variations in the X-ray output of black holes to produce just this sort of music," Uttley said.
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Long and short of it
The goal of the study was to compare the two types of black holes, the stellar gravity wells gorging on their binary companions and the supermassive variety fed by the material of entire galaxies.
Uttley and McHardy found that notes from stellar black holes vary rapidly, on time-scales of milliseconds to seconds. Supermassive black holes play more ponderously, though, with variations taking about a million times longer, on average.
"In other words, take the tune played out in X-rays by a black hole X-ray binary and slow down the tape by a factor of a million or so and you get the kind of variations we are seeing in active galaxies" anchored by supermassive black holes, Uttley said.
The study further revealed that at any given moment, various black holes are playing different styles of music; instead of some organized celestial symphony; there is a cacophony of differing styles playing out all over the galaxy.
And every few weeks, a stellar black hole switches musical styles, undergoing a distinct transition from one pattern of variability to another.
"Astronomers think that these 'state transitions,' which last several weeks, may represent changes in the mode of accretion, caused by changes in the rate of fuel supplied to the black hole," Uttley said. "Taking the musical analogy a step further, you could liken the new state to a different musical style."
Further observations will be required to learn if supermassive black holes are capable of playing a similar range of styles.
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