I Know Why the Black Hole Sings

July 08, 2009

Black Hole Week is still going strong here at Twisted Physics. There's no end to surprising facts about these enigmatic objects. One of my favorite black hole discoveries of the last few years was the 2003 detection of a "singing black hole" at the center of a galaxy in the Perseus Cluster, some 250 million light years from Earth. It's not actually trilling its way through a famous operatic aria like "Nessun Dorma" -- Luciano Pavarotti's reputation is secure -- and it only sings one note: B flat. But it is the lowest possible B flat ever detected.

The Cambridge University scientists used the middle C note on a piano keyboard as a reference point when determining where the droning note emitted by the black hole would fall on the musical scale. On a keyboard, the B Flat nearest middle C is 1-1/2 steps away.

The black hole's B Flat, however, is a whopping 57 octaves below middle C -- one million, billion times lower than what the human ear can detect. That gives the sound waves a frequency of 10 million years, compared to 1/20th of a second.

They are the result of the sound waves, transmitted through the bits of dust and gas that make up the interstellar medium. Chandra saw lots of concentric ripples in the interstellar medium -- ripples the size of 30,000 light years. The actual ripples are caused by gravitational effects from all those galaxies clumped together in the Perseus Cluster. The black hole pulls matter in, but in the process jets of material shoot out around it, creating pressure waves. And to scientists, pressure waves are just sound waves. Anyway, it was this X-ray radiation that NASA's Chandra X-Ray Observatory detected in 2003, providing indirect evidence of a "singing" black hole.

Because they carry acoustical energy, those sound waves keep the gas dispersed throughout the cluster warmer than it would otherwise be. It's not just a bizarre acoustical curiosity, either: those warmer temperatures regulate the rate at which new stars form, so the sound waves could prove to be critical to our understanding of how the universe's structure evolves.

Our musical black hole in the Perseus cluster might be a one-note wonder, but Pavarotti never promised to unlock the secrets of galaxy formation. We're just sayin'....

Image: Sound waves from a black hole in the Perseus Cluster. Source: NASA/Chandra.

Comments

[Yoo]

Is it really due to Hawking radiation? Wouldn't it be far too weak to have any real effect?

I thought the sounds from the black hole were due to interactions in the accretion disk ...

[Karen]

It's a small point, really, and not at all about the fabulous physics involved, but the nearest B Flat to middle C on a keyboard is actually a whole step away, not a step and a half. Musical intervals are measured in half steps and whole steps. And the musical intervals in an octave (ascending or descending) are as follows: minor second, major second, minor third, major third, pefect fourth, tri-tone, perfect fifth, minor sixth, major sixth, minor seventh, major seventh, octave. So, a B Flat is a descending major second from middle C.

[Fred]

"a frequency of 10 million years"?

Or possibly a 'period'?