The Sound of a Black Hole

Snags writes "Astronomers have used the Chandra X-ray Observatory to observe the deepest, lowest-frequency sound waves ever observed. By my calculations, the 'B-Flat 57 octaves below middle-C' has a period of 9.8 million years. Despite arguments that explosions in space movies should be silent, it is legitimate to call these sound waves because at that frequency, particles of space dust can 'see' each other through gravity. These notes are 'over a million billion times deeper than the limits of human hearing', so to call it infra-sound would be a bit of an understatement."

Comments

This would be a "RTFA". It *is* sound.

[JeanPaulBob]

Read the Space.com link.

The Perseus cluster is the brightest known in X-rays, making it a good target for study. It has two large, bubble-shaped cavities that extend away from a central black hole. The cavities are formed by jets of material ejected from the black hole's surroundings, and the jets have been suspected of heating the outlying gas. But scientists couldn't see how.

A special image-processing technique was used to bring out subtle changes in brightness that revealed the presence of ripples -- the sound waves.

Fabian and Allen figure the sound waves, observed spreading out from the cavities, heat the gas. The amount of energy involved is staggering, equal to what would be produced if 100 million stars exploded.

They're not saying that infra-radiation is sound--they used the telescope to see ripples in the gas. That's the sound.

Re:On the team

[xiox]

Good question. If you look at the ripple image (generated by unsharp masking), you'll see the waves aren't perfectly spaced, so there's an error there. We estimate a wavelength of about 11 kpc. You then need the sound speed, which is a function of temperature (about 1170 km/s in gas of about 5 keV). The calculation of the period of 10^7 years is probably a good estimate, but it isn't precise. If you're really interested in the details read the original paper here.

Re:Do black holes exist?

[Bonker]

Thinking of "curves" in space-time is an interesting analogy for gravity, but still doesn't address the mechanism - sure, the planet may be on a "45 degree" incline in spacetime, but what forces it down... and not up? You would nearly have to posit the existence of some constant stream of gravitons coming at 'right angles' to three-dimensional space in order to actually push things 'down the well'.

The best explantion for this I've ever heard deals entirely with special relativity and never touches quantum mechanics. The author I read (Epstein) discusses what he calls 'Slow Time'. An object is always moving in four dimenions, even if it appears at rest to an observer, because it is moving forward in time as well. Since all dimensions of space and time are warped by the presence of matter, and not just space, if the object being observed is closer to a source of gravity (on a steeper part of the curve of space-time), he will start to experience time shortening or time dialation sooner and more strongly than you, the observer. His straight-line path through time starts to curve toward the source of gravity. This time-dialation acts as a vector force to 'push' him towards the source of gravity.

You can read more about the interperatation of Special Relativity in this book: Relativity Visualized