Sound in space?

[The_Flying_Dutchman]

In the news today is the discovery of the deepest sound in space. From one of several sites on Google News the report goes:

Big black holes sing bass. One particularly monstrous black hole has probably been humming B flat for billions of years, but at a pitch no human could hear, let alone sing, said an astronomer from the Institute of Astronomy at Cambridge, England.

“The intensity of the sound is comparable to human speech,” said one astronomer. But the pitch of the sound is about 57 octaves below middle C, roughly the middle of a standard piano keyboard. This is far, far deeper than humans can hear, the researchers said, and they believe it is the deepest note ever detected in the universe.

The sound is emanating from the Perseus Cluster, a giant clump of galaxies some 250 million light-years from Earth. A light-year is about 6 trillion miles, the distance light travels in a year.

First of all, I always thought that sound can not propagate in space. Am I wrong?

Secondly, given the source of this sound, at a distance of 250 million light years away, and given the speed of sound in air (my understanding is that the speed of sound in a vacuum is 0 or in a partial vacuum approaches 0) is 343 m/s as opposed to the speed of light in a vacuum at 299,792,458 m/s, even at air speed, this discovery would suggest that the universe is at least 1 million times older than previously thought. Where did I go wrong?

[hammerbach]

Well, with that C being about 525 cycles per second, I guess that means the black hole emits 3.6429X10e-15 cycles per second (divide by 2 fifty-seven times). The wavelength, at least where I am, would be 2.9647x10e17 feet, so a flute with that fundamental pitch would have to be

[hammerbach]

Well, with that C being about 525 cycles per second, I guess that means the black hole emits 3.6429X10e-15 cycles per second (divide by 2 fifty-seven times). The wavelength, at least where I am, would be 2.9647x10e17 feet, so a flute with that fundamental pitch would have to be 3.5093x10e

[dinoboy]

I get some pretty crazy numbers too: if sound is (at 1 atm) about 847000 times slower than light, and the light was 250 million years away - …Thats close to 2.18 x 10^14 years! (this is about 14 thousand times older than our current estimate of between 12 and 20 billion years). There is also the added problem that sound travels even slower in colder air. Hmmm, If you went wrong, I’m following…

Maybe it’s a trick… Any astrophysicists in the house?

[Marley23]

First of all, I always thought that sound can not propagate in space. Am I wrong?

I think you’re right. Sound needs a medium to travel through, and space is a poor one.

this discovery would suggest that the universe is at least 1 million times older than previously thought.

I’m not sure what’s wrong with that, but it’s obviously not the case or someone would’ve noticed pretty darn fast.

[hammerbach]

Sigh… must avoid button…
That would be 3.5093x10e9 Earth diameters long. Now where am I going to find a lathe that big…

I suppose what they mean is that it has been observed to vibrate in a periodic way with that frequency. Sound does not have to propagate through space to exist or to be observed. (Although I’m not sure I would call that sound. If a black hole vibrates at unimaginably low frequency, and nobody is there to hear it, does it still make a sound?)

Maybe ** The Bad Astronomer** will drop by for comment…

[The_Bad_Astronomer]

Sound cannot travel through a vacuum, but space is rarely a perfect vacuum. Galaxies have nebulae, giant gas clouds, and sound travels through them. That’s why you get ribbons and sheets in, for example, the Vela supernova remnant.

In this case, the black hole is surrounded by the intercluster medium, the gas between galaxies. Somehow energy from the black hole is being pumped into the gas in the form of sound waves. Even from the full press release, it’s unclear to me how that’s being done. I’ll keep my eyes open for a journal paper about this.

[The_Flying_Dutchman]

Thanx for the improved cite on this report The Bad Astronomer

The link pretty well clears up the misunderstanding I had about the way thew sound was detected. I thought of some audio sensor on earth, rather than visual evidence of sound waves in a localized region.

[alimarx]

*Originally posted by grienspace *
But the pitch of the sound is about 57 octaves below middle C, roughly the middle of a standard piano keyboard.

Dang, and I thought I sang flat…