The question of the loudest sound ever recorded in space presents a paradox. On Earth, sound is understood as mechanical vibrations traveling through a medium like air or water, but the cosmos is often depicted as a silent void. Seeking the loudest noise requires moving beyond the familiar definition of sound and exploring the extreme physics of the universe. This leads to the detection of immense energy waves that, while not audible to human ears, represent the most powerful acoustic-like phenomena ever measured. To find the loudest cosmic “sound,” one must first understand why most of space is fundamentally silent.
The Fundamental Physics of Silence
Sound waves are fundamentally mechanical waves, meaning they require a physical medium—such as a solid, liquid, or gas—for their energy to be transmitted. The sound we hear is the result of vibrating molecules bumping into their neighbors, passing the energy along until it reaches our eardrums. In the absence of a sufficient number of molecules, the energy cannot propagate effectively.
Interstellar and intergalactic space is a near-perfect vacuum, characterized by an extreme scarcity of matter. The particle density is so low that atoms are often separated by vast distances. This immense distance prevents the chain reaction of molecular collisions necessary for a coherent sound wave to form and travel. Consequently, any explosion or sound-producing event in the vacuum of space would be acoustically silent in the traditional sense.
Sound Analogues in Intergalactic Mediums
Despite the general silence of the vacuum, some regions of the cosmos are dense enough to support acoustic-like waves. These areas are typically found within galaxy clusters, which are filled with a superheated, low-density gas known as plasma. This plasma is an ionized medium of charged particles that, while far less dense than Earth’s atmosphere, is dense enough to transmit pressure disturbances.
These cosmic sound analogues are generated by powerful events, such as supermassive black holes or galaxy collisions, creating ripples in the surrounding plasma. Unlike sound on Earth, these waves travel incredibly slowly, often taking millions of years to complete a single oscillation cycle. Their frequencies are far below the range of human hearing, which typically extends down to about 20 Hertz. The ability of this plasma to act as a medium allows astronomers to measure these pressure changes using instruments that detect X-rays, providing a way to “listen” to the cluster’s thermal history.
The Actual Cosmic Loudest Sound
The most powerful acoustic wave ever detected originated from the supermassive black hole at the center of the Perseus Galaxy Cluster. Discovered in 2003 by NASA’s Chandra X-ray Observatory, this black hole was found to be generating colossal pressure waves that rippled through the cluster’s hot gas envelope, which is located approximately 240 million light-years from Earth. The figurative “loudness” of this event is a measure of the sheer energy involved in creating the disturbance.
The wave itself was identified as the deepest note ever recorded in the universe, corresponding to the musical note B-flat. Its frequency was calculated to be 57 octaves below middle C, a pitch so low that one cycle of the wave would take about 10 million years to complete. This ultra-low frequency wave is a consequence of the black hole periodically erupting, injecting huge amounts of energy into the surrounding gas and carving out enormous cavities. The immense scale of this energy release, equivalent to trillions of times the power of the Sun, earns it the title of the universe’s loudest recorded sound.
Translating Cosmic Waves into Auditory Experience
Since the black hole’s pressure waves are at a frequency far too low for human hearing, scientists use a process called sonification to make them audible. Sonification involves taking astronomical data, such as the X-ray data collected by the Chandra telescope, and translating it into sound. This is not the direct recording of sound, but rather the conversion of data points into auditory signals.
To bring the Perseus black hole’s B-flat into the human hearing range, scientists had to dramatically increase its frequency. The data was scaled up by 57 and 58 octaves, making the wave audible at frequencies 144 quadrillion and 288 quadrillion times higher than its original pitch. This scaling process compresses millions of years of oscillation into seconds, allowing listeners to perceive the sound as an eerie, deep tone. This translation offers a way for the public and researchers to experience the universe’s powerful, otherwise inaudible, acoustic phenomena.