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Q&A: Galaxies, Galaxy Clusters, AGN, and Quasars

Q:
What is the uncertainty in the frequency of this sound discovered in Perseus? By specifying the note (to the 1/2 step) you are implying a precision of about 6%. Do we know the distance to the Perseus cluster and the speed of sound in the intergalactic gas well enough to support this small an error?

A:
The scientists give a period for the sound waves, which can be converted to a frequency. The nearest note that this corresponds to is a B-flat 57 octaves below the B-flat above middle-C. The scientists do not quote errors for their period estimate, but there are a number of sources of uncertainty, and we would estimate that the total error is in fact larger than 6%. However, even if the scientists had done an error analysis, an error discussion isn't appropriate for a press release, so a degree of mathematical naivete is acceptable.

The interesting point about the "note" is not whether it is a B-flat or a C, or an A, but that it is so many octaves below middle-C. These are extraordinarily large sound waves.

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