It's often said that in space, you can't hear yourself scream. True enough, more or less, but rather misleading. Recently, several SPACE.com readers wrote to ask how a B-flat emanating from a black hole could be detected from 250 million light-years away, as we reported earlier this month.
The answer, along with related interesting facts, reveals that silence is in the ear of the beholder, and ears come in a variety of configurations.
Sound can travel through space, because space is not the total vacuum it's often made out to be. Atoms of gas give the universe a ubiquitous atmosphere of sorts, albeit a very thin one.
Sound, unlike light, travels by compressing a medium. On Earth, the atmosphere works well as a sound-carrying medium, as does water. The planet itself is very adept at transmitting an earthquake's seismic waves, a form of sound.
Space, though not as efficient, can also serve as a medium.
If a brave and clever astronaut could safely remove her helmet and shout into the cosmos, her voice would carry.
"We wouldn't be able to hear the sound because our ears aren't sensitive enough," explains Lynn Carter, a graduate student in astronomy at Cornell University. Not enough atoms -- if any -- would strike our eardrums. "Maybe if we had an amazingly large and sensitive microphone we could detect these sounds, but to our human ear it would be silent."
An amazingly sensitive microphone, in a sense, was used to discover the constant B-flat coming from the black hole [Story here]. NASA's Chandra X-ray Observatory observed gas, compressed by the sound, in concentric rings much like ripples on a pond.
I am not sure how big a parsec is but at 250 million lightyears a ship would have to be able to travel 13 billion times the speed of light to move farther then that detection distance in one turn/week. The article also states:
The black hole under study sits amid a cluster of galaxies, a region of space where gas is denser than the universe on average.
I am not an expert in astro physics, but it would seem reasonable to me that in certain places, possibly close to suns or planets, that with the right equipment you could detect the sound coming from a ship. Also, if a ship does leave a engine trail and you were to cross that path the noise could vibrate that engine trail to the point where it was detectable. In the end this is all science fiction and who is to say what is possible and not possible.