Sound waves reported by NASA
Hi all, I have a question that bothers me a little about this release from NASA: http://science.nasa.gov/headlines/y2003/09sep_blackholesounds.htm?list726251 The argument is that the structures seen by Chandra around a supermassive black hole in the Perseus Cluster are evidence of sound waves booming through the surrounding gas. The sound waves "sweep across hundreds of thousands of light years," the Chandra folks say at: http://chandra.harvard.edu/photo/2003/perseus/more.html. The problem I have is that surely, those hundreds of thousands of light years encompass mostly vacuum. What mechanism could allow an excited gas atom 300 miles away from the next atom to pass along sound? Doesn't it require physical contact? If not, I guess those old Flash Gordon movies were right after all, and we should hear the buzz as those sparkler-driven spaceships cruise the interstellar medium. Thanks, Joe Joe Bauman science & military reporter Deseret News bau@desnews.com (801) 237-2169
Joe, the frequency is dozens of octaves lower than anything humans would relate to as "sound". If it helps, think of it more as a pressure wave in a rareified "atmosphere", even an atmosphere with only a molecule or two per cubic meter- when you remember just how huge this "structure" is, even if there is only one molecular interaction per cubic kilometer, at this scale it is sufficient to propagate the wave. Another reminder just how big space is, and how small we and our world are. C. --- Joe Bauman <bau@desnews.com> wrote:
Hi all, I have a question that bothers me a little about this release from NASA:
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Granted, it's not truly sound, it's pressure -- but in a rarified medium with one molecule per cubic km., what's the physical process that causes that one molecule to bump into the next one, a km. away? I can't imagine how else this pressure wave is passed. Thanks, Joe Joe Bauman science & military reporter Deseret News bau@desnews.com (801) 237-2169
The process is mechanical, the same as sound in the human range, even though the individual molecules are kilometers apart. You are thinking correctly about the process, the problem seems to be convincing yourself of it! C. --- Joe Bauman <bau@desnews.com> wrote:
Granted, it's not truly sound, it's pressure -- but in a rarified medium with one molecule per cubic km., what's the physical process that causes that one molecule to bump into the next one, a km. away? I can't imagine how else this pressure wave is passed. Thanks, Joe
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On 10-Sep-03 8:25, Chuck Hards wrote:
The process is mechanical, the same as sound in the human range, even though the individual molecules are kilometers apart. You are thinking correctly about In space, the density of molecules is closer to tens to millions per cubic meter, not km. In the region of a gas cloud, the density would be many thousands to millions of particles per cubic meter. Only in the deepest part of intergalactic space could the density drop near the particle/km^3.
Hence, it is not very difficult to propogate a pressure wave by mechanical interactions. The propogation speed (speed of sound) is _very_ low compared to a normal atmosphere; very easy to go Mach 1! :) -- 101 USES FOR A DEAD MICROPROCESSOR (100) Killer velcro
This should make it easier for Joe to believe that it's truly a pressure-wave phenomemon. I was merely speaking off the cuff, not attempting to truly quantify the interstellar density. Hard to be precise when at work with my mind wrapped around composites instead of astro-physics. Thanks C. --- Paul Gettings <gettings@mines.utah.edu> wrote:
On 10-Sep-03 8:25, Chuck Hards wrote:
The process is mechanical, the same as sound in the human range, even though the individual molecules are kilometers apart. You are thinking correctly about In space, the density of molecules is closer to tens to millions per cubic meter, not km. In the region of a gas cloud, the density would be many thousands to millions of particles per cubic meter. Only in the deepest part of intergalactic space could the density drop near the particle/km^3.
Hence, it is not very difficult to propogate a pressure wave by mechanical interactions. The propogation speed (speed of sound) is _very_ low compared to a normal atmosphere; very easy to go Mach 1! :)
-- 101 USES FOR A DEAD MICROPROCESSOR (100) Killer velcro
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participants (3)
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Chuck Hards -
Joe Bauman -
Paul Gettings