Outer space is generally thought of as a silent void, given that sound waves require a medium like air or water to travel through. However, there are sources in space that generate intense bursts of energy that could be considered extremely “loud” by earthly standards.
How Sound Travels in Space
Sound is created by vibrations or pressure waves that cause matter to oscillate as the energy travels through it. On Earth, most sounds are carried by vibrations passing through the air. In the vacuum of space, however, there is no air for sound waves to travel through.
Sound can travel through solid objects, liquids, and gases because the molecules in these mediums are elastic and compressible. When a sound wave encounters matter, it causes the particles to oscillate back and forth, transmitting the energy. In a vacuum like space, there are no particles to disturb, so regular sound waves cannot propagate.
However, space is not a total vacuum. There are some particles floating around, as well as magnetic and electromagnetic radiation. Explosions or other high-energy events can theoretically cause vibrations in these mediums that could be interpreted as sound.
Measuring Sound in Space
On Earth, the loudness of sound is usually measured in decibels (dB) on a logarithmic scale. The softest audible sounds, like rustling leaves, are about 10 dB. Normal conversation is around 60 dB. Prolonged exposure to noises above 85 dB can cause hearing damage. The loudest sounds, like rocket launches, register over 200 dB.
In space, though, decibels are not very useful since they are calibrated for sounds perceived by the human ear in an atmosphere. Astrophysicists instead might talk about the amount of energy released by an event. Higher energy emissions correspond to more intense sounds.
Sources of Intense Acoustic Energy in Space
Here are some phenomena in space that generate tremendous amounts of energy that could be interpreted as loud sounds:
Supernovae
When a massive star reaches the end of its life, it can explode in an event called a supernova. This catastrophic blast radiates as much energy in a few seconds as the Sun will produce over its entire lifetime. The emitted energy takes the form of neutrinos, electromagnetic radiation across the spectrum, and gravitational waves. Researchers have translated signals from supernovae into audible sounds. The acoustic energy would be equivalent to hundreds of decibels if heard from a safe distance.
Pulsars
Pulsars are rapidly spinning neutron stars that emit intense beams of electromagnetic radiation from their polar regions. As the star rotates, the beams sweep across space like the beam from a lighthouse. To an observer in the path, the signals are perceived as extremely regular pulses of energy. The repetitive bursts have been converted to periodic chirps and other sounds. The initial blast of a supernova that creates a pulsar would register over 200 dB.
Quasars
Quasars are massive black holes at the center of galaxies that are accreting huge amounts of material. The infalling gas and dust heats up and shoots out powerful jets of radiation. Quasars are among the brightest objects in the universe and the energy output is immense. The acoustic noise from a quasar would approach or exceed 200 dB based on the quantity of emitted radiation.
Cosmic Microwave Background
The cosmic microwave background (CMB) is thermal radiation left over from the Big Bang that fills all space. Mapping the tiny fluctuations in the CMB has revealed details about the early universe. While the CMB corresponds to electromagnetic microwaves, not sound, its intensity pattern has been translated into acoustic signals. Research has found an anomalous cold spot in the CMB that contains mass equivalent to 10 million black holes. The sound from such a concentration of mass would register an estimated 270 dB if it could be heard.
Loudest Known Events
Here are some of the most intense sound-generating events that have been detected originating from space:
| Event | Estimated Loudness |
|---|---|
| Magnetar starquake on SGR 1806-20 | 230 dB |
| Swift J1644+57 black hole collision | 210 dB |
| Merging black hole GW150914 | 210 dB |
| Gamma-ray burst GRB 030329 | 200 dB |
Magnetars are extremely magnetized neutron stars that can flare and rupture their crusts in events called starquakes. In 2004, sensors detected a massive burst of gamma and X-rays from magnetar SGR 1806-20 some 50,000 light-years away. NASA scientists calculated the energy release was equivalent to a 230 dB sound. Stars collapsing into black holes can also generate tremendous acoustic energy. A 2014 black hole collision registered 210 dB, as did the first detected gravitational wave signal GW150914 from two merging black holes.
Sounds Generated by Human Activity
While natural cosmic events can produce the most intense noises, sounds generated by human-built spacecraft and equipment can also be very loud in space.
Rocket Launches
The controlled explosions inside rocket engines that propel spacecraft like the Saturn V or Space Shuttle to orbit are deafening. Nearby sound levels reach about 200 dB during launch. The roar and rumble is greatly reduced just dozens of meters away after passing through an exhaust plume. However, solid rocket boosters like the SRBs on the Space Shuttle registered 190 dB inside the case before ignition while sitting on the pad fully fueled.
Pyrotechnic Devices
Spacecraft use small pyrotechnic charges for actions like emergency escape tower jettison or payload fairing separation. These tiny explosive devices produce brief, intense bursts of sound measuring over 170 dB. The noise quickly attenuates without an atmosphere.
Astronaut Suits
The life support systems on spacesuits like the Apollo Extravehicular Mobility Unit or Shuttle Extravehicular Mobility Unit release oxygen and ventilation gas and circulate water for cooling. All these systems generate vibrations and noise. A study found sound levels inside an EMU reached about 80 dB, similar to a kitchen blender.
Sounds Heard by Astronauts in Space
While space itself carries no sound, astronauts in spacecraft or space stations do experience noises from equipment, experiments, and activities:
On Space Shuttles
- Middeck: 72-77 dB, like an alarm clock
- Flight deck: 65-70 dB, like normal conversation
- Toilet fans: 85 dB, like a hairdryer
- Waste collection: 120 dB, like a thunderclap
On the International Space Station
- United States segment: 60 dB, like an office
- Russian segment: 68 dB, like a noisy restaurant
- Exercise equipment: 75-85 dB, like a blender
- Life support fans: 55-80 dB, like rainfall
Noises in the space environment are very directional since there is no air to help dissipate sound waves. Astronauts report equipment noises can be irritating and sleep-disrupting. Headphones and background music are often used to provide relief.
Conclusion
While sound does not travel through the vacuum of space, immense bursts of energy from cosmic events like colliding black holes and magnetar starquakes can generate waves that would register hundreds of decibels if detected from a safe distance. Closer to home, the controlled explosions that launch rockets and pyrotechnic devices on spacecraft also produce extremely loud noises. But without air to transmit the vibrations, these sounds quickly fade once they interact with nearby surfaces. Astronauts in orbit do experience equipment noises in spacecraft and spacesuits that can affect comfort and sleep quality during long-duration missions.
