Space is not a homogeneous nothing. Between various objects there are clouds of gas and dust. They are the remnants of supernova explosions and the site for star formation. In some areas, this interstellar gas is dense enough to propagate sound waves, but they are not susceptible to human hearing.
Is there sound in space?
When an object moves - be it the vibration of a guitar string or an exploding firework - it affects nearby air molecules, as if pushing them. These molecules crash into their neighbors, and those, in turn, into the next ones. Movement spreads through the air like a wave. When it reaches the ear, the person perceives it as sound.
When a sound wave passes through air, its pressure fluctuates up and down like sea water in a storm. The time between these vibrations is called the frequency of sound and is measured in hertz (1 Hz is one oscillation per second). The distance between the highest pressure peaks is called the wavelength.
Sound can only propagate in a medium in which the wavelength is not more thanaverage distance between particles. Physicists call this "conditionally free road" - the average distance that a molecule travels after colliding with one and before interacting with the next. Thus, a dense medium can transmit short wavelength sounds and vice versa.
Long wave sounds have frequencies that the ear perceives as low tones. In a gas with a mean free path greater than 17 m (20 Hz), the sound waves will be too low frequency to be perceived by humans. They are called infrasounds. If there were aliens with ears that can hear very low notes, they would know for sure if sounds can be heard in outer space.
Black Hole Song
Around 220 million light-years away, at the center of a cluster of thousands of galaxies, a supermassive black hole is humming the lowest note the universe has ever heard. 57 octaves below middle C, which is about a million billion times deeper than human hearing.
The deepest sound humans can hear has a cycle of about one vibration every 1/20th of a second. A black hole in the constellation Perseus has a cycle of about one oscillation every 10 million years.
This came to light in 2003, when NASA's Chandra Space Telescope discovered something in the gas filling the Perseus Cluster: concentrated rings of light and dark, like ripples in a pond. Astrophysicists say that these are traces of incredibly low-frequency sound waves. brighter -these are the tops of the waves where the pressure on the gas is greatest. The darker rings are depressions where the pressure is lower.
Sound you can see
Hot, magnetized gas swirls around a black hole, like water swirling around a drain. As it moves, it creates a powerful electromagnetic field. Strong enough to accelerate gas near the edge of a black hole to almost the speed of light, turning it into huge bursts called relativistic jets. They force the gas to turn sideways on its way, and this effect causes eerie sounds from space.
They travel through the Perseus Cluster hundreds of thousands of light-years from their source, but sound can only travel as long as there is enough gas to carry it. So it stops at the edge of the gas cloud filling the Perseus galaxy cluster. This means that it is impossible to hear its sound on Earth. You can only see the effect on the gas cloud. It looks like looking through space at a soundproof camera.
Strange planet
Our planet lets out a deep groan every time its crust moves. Then there is no doubt whether sounds propagate in space. An earthquake can create vibrations in the atmosphere with a frequency of one to five Hz. If it is strong enough, it can send infrasonic waves through the atmosphere into outer space.
Of course, there is no clear boundary where the Earth's atmosphere ends and space begins. The air just gradually gets thinner until eventuallydisappears altogether. From 80 to 550 kilometers above the Earth's surface, the mean free path of a molecule is about a kilometer. This means that the air at this altitude is about 59 times thinner than it would be possible to hear sound. It can only carry long infrasonic waves.
When a magnitude 9.0 earthquake rocked the northeast coast of Japan in March 2011, seismographs around the world recorded its waves passing through the Earth, and the vibrations caused low-frequency vibrations in the atmosphere. These vibrations have traveled all the way to where the European Space Agency's Gravity Field and the stationary Ocean Circulation Explorer (GOCE) satellite compare Earth's gravity in low orbit to 270 kilometers above the surface. And the satellite was able to record these sound waves.
GOCE has very sensitive accelerometers on board that control the ion thruster. This helps keep the satellite in a stable orbit. On March 11, 2011, GOCE accelerometers detected a vertical shift in the very thin atmosphere around the satellite, as well as undulating shifts in air pressure, as sound waves from an earthquake propagate. The satellite's thrusters corrected the offset and stored the data, which became something like an earthquake infrasound recording.
This entry was classified in the satellite data until a team of scientists led by Rafael F. Garcia released this document.
The first sound inuniverse
If it were possible to go back in time, to about the first 760,000 years after the Big Bang, we could find out if there is sound in space. At that time, the universe was so dense that sound waves could travel freely.
Roughly around the same time, the first photons began to travel through space as light. After that, everything finally cooled down enough for subatomic particles to condense into atoms. Before the cooling occurred, the universe was filled with charged particles - protons and electrons - that absorbed or scattered photons, the particles that make up light.
Today it reaches Earth as a faint glow of the microwave background, visible only to very sensitive radio telescopes. Physicists call this relic radiation. It is the oldest light in the universe. It answers the question of whether there is sound in space. The CMB contains a recording of the oldest music in the universe.
Light to help
How does light help us know if there is sound in space? Sound waves travel through air (or interstellar gas) as pressure fluctuations. When the gas is compressed, it gets hotter. On a cosmic scale, this phenomenon is so intense that stars form. And when the gas expands, it cools down. Sound waves propagating through the early universe caused slight pressure fluctuations in the gaseous environment, which in turn left subtle temperature fluctuations reflected in the cosmic microwave background.
Using temperature changes, physicsUniversity of Washington John Kramer managed to restore these eerie sounds from space - the music of the expanding universe. He multiplied the frequency by 1026 times so that human ears could hear him.
So no one really hears the scream in space, but there will be sound waves moving through clouds of interstellar gas or in the rarefied rays of Earth's outer atmosphere.
